Adjusted Cost Base in Canada: How to Calculate and Track It

Your adjusted cost base is what an investment has cost you, kept up to date. Not the price on the day you first bought it, and not whatever figure your broker happens to print on a slip. It is a running total: every dollar you have put into that holding, plus the fees you paid to acquire it, changed every time something happens that changes what it cost you. When you eventually sell, the tax you owe is measured against that running total and nothing else.

Most people treat it as a number they can look up. It is a number you have to keep, and Canada puts the job on you rather than on the institution holding the shares.

Here is what that costs when nobody keeps it. Take 100 shares of Royal Bank bought on July 24, 2024, enrolled in a dividend reinvestment plan, and sold nine quarters later. Done correctly, the capital gain is $13,847.74. Reported from the original purchase price, because the reinvestments were never written down, the gain is $15,290.07. The difference is $1,442.33, and $1,442.33 is exactly what the plan reinvested over those nine quarters, which is money that was already taxed as dividend income in each of the years it was paid. Ignoring your own cost base does not simplify anything. It makes you pay tax twice on the same dollars, and the second bill is one you volunteered for.

This guide covers the whole system: what belongs in the pool, the averaging rule that makes it a pool in the first place, the five events that move it, and the two traps that cost the most money. Ontario is used wherever an example needs a tax rate, because arithmetic needs a province. Every mechanic described here is federal and identical everywhere in the country.

What an adjusted cost base is, in the CRA’s own words

The Canada Revenue Agency’s definitions for capital gains page puts it in one sentence:

> “Adjusted cost base (ACB) This is usually the cost of a property plus any > expenses to acquire it, such as commissions and legal fees.”

The word doing the work is “adjusted”. The cost is not frozen at purchase. The Income Tax Act handles this in two mirrored lists. Subsection 53(1) opens: “In computing the adjusted cost base to a taxpayer of property at any time, there shall be added to the cost to the taxpayer of the property such of the following amounts in respect of the property as are applicable”. Subsection 53(2) is the same sentence with “there shall be deducted”.

Read “shall be added” carefully. It is not an election, a concession or a planning opportunity you can choose to take up. The additions are mandatory, which is precisely why failing to track them costs money instead of saving effort. Every upward adjustment you fail to record is a deduction the Act already granted you and you declined to claim.

One formula runs the whole subject:

Capital gain = proceeds of disposition minus (adjusted cost base plus outlays and expenses).

Outlays and expenses are their own defined term on the same CRA page:

> “Outlays and expenses These are amounts that you incurred to sell a capital > property. You can deduct outlays and expenses from your proceeds of > disposition when calculating your capital gain or loss.”

Half of the resulting gain is taxable under section 38 of the Act, and half of a loss is the allowable capital loss you can apply against gains. What that half costs you depends on your own bracket, which our guide to how investment income is taxed works through to the cent.

What goes in, and what stays out

The single most common error in this whole area is a fee in the wrong place. A commission you pay to buy goes into the cost base. A commission you pay to sell does not. It is an outlay on the disposition and comes off the proceeds separately. The arithmetic lands in the same direction either way, which is why people get away with mixing them up on a simple trade, but the two numbers live on different lines and they behave differently the moment you own the shares in more than one lot.

Item	Treatment	Why
Price paid for the shares	Goes into the ACB	The CRA’s definition: “the cost of a property”
Commission paid to buy	Goes into the ACB	“plus any expenses to acquire it, such as commissions and legal fees”
Legal or other fees to acquire	Goes into the ACB	Same definition
Dividends reinvested by a plan	Goes into the ACB	Each reinvestment is a purchase of more shares at a price
A superficial loss that was denied	Added to the replacement shares’ ACB	ITA s.53(1)(f)
Return of capital distributions	Comes out of the ACB	ITA s.53(2), reported in T3 box 42
Commission paid to sell	Not in the ACB	It is an outlay on the disposition, subtracted from proceeds
A cash dividend you did not reinvest	No effect	It is income in the year received, not a change in cost
The share price going up or down	No effect	Cost base tracks what you paid, never what it is worth
Selling part of your holding	No effect on cost per share	T4037: “Dispositions of identical properties do not affect the ACB”

If you are still working out where commissions land on a first trade, the mechanics of placing the order and what the confirmation shows you are in our guide to buying your first stock.

One boundary before anything else. There is no adjusted cost base inside a TFSA, an RRSP, an FHSA, a RRIF or an RESP, and nothing that happens inside those accounts goes on Schedule 3. Cost base is a non-registered problem exclusively. That sounds like relief, and for most of this guide it is. In the superficial loss section it turns into the most expensive fact on the page.

The averaging rule: one pool per holding, across every account you own

Buy the same shares twice at different prices and you do not own two lots. You own one pool at one average price. CRA Guide T4037, the capital gains guide, sets out what counts as the same thing:

> “Properties of a group are considered to be identical if each property in the > group is the same as all the others. The most common examples of identical > properties are shares of the same class of the capital stock of a corporation > or units of a mutual fund trust.”

And what you have to do about it:

> “You may buy and sell several identical properties at different prices over a > period of time. If you do this, you have to calculate the average cost of > each property in the group at the time of each purchase to determine your > ACB.”

The method is the obvious one, stated by the CRA so there is no argument about it: “The average cost is calculated by dividing the total cost of identical properties purchased (this is usually the cost of the property plus any expenses involved in acquiring it) by the total number of identical properties owned.”

Three consequences follow, and each of them catches somebody.

The recalculation happens at every purchase, not at year end. The average moves the moment you buy, and the figure that matters on a later sale is the average as it stood then.

Dispositions do not move the average. T4037 again: “Dispositions of identical properties do not affect the ACB.” Sell a third of your position and the pool shrinks by the cost of the shares that left, at the average. The cost per share of what remains is unchanged. Selling does not reset anything and it does not crystallise a new basis for the rest.

The pool is yours, not your account’s. One average per identical property per taxpayer, across every non-registered account you hold, at every institution. The same shares in a cash account at one broker and a margin account at another are one pool. Neither broker can see the other, so neither broker can compute your number. They compute theirs, which is a different number that happens to share a name.

Canada does not have lot selection

This is worth stating flatly because it is the assumption most often imported from elsewhere. There is no first in first out here, no last in first out, no specific identification, no choosing which shares you sold to manage the gain. Investors who have filed in the United States frequently expect to pick a lot and find the option in their broker’s interface. Canadian tax does not work that way: the shares are identical, the pool is averaged, and the gain on any sale is measured against that single average.

Box 20 on your T5008 is a starting figure, not an answer

Your broker issues a T5008 for dispositions, and box 20 carries a cost or book value. It is the broker’s view of what the shares cost in the account it can see, and the CRA expects you to adjust it yourself before it goes anywhere near a return. It is a useful starting point and a bad ending point, for exactly the reasons above: a second account elsewhere, a reinvestment plan, a return of capital, a denied loss. Our research piece on what box 20 on a T5008 actually reports works through where the broker’s figure and your figure separate.

Everything that moves the pool after you buy

Five events change an adjusted cost base once the shares are yours. This table is the reference version of the rest of the guide.

Event	Direction	Where you see it	Authority
Another purchase of the same shares	Pool up, average recalculated	Trade confirmation	T4037, identical properties
A dividend reinvested by a plan	Pool up, average recalculated	DRIP statement or confirmation	ITA s.53(1)
Return of capital	Pool down	T3 slip, box 42	ITA s.53(2), T4037 box 42
A denied superficial loss	Pool up on the replacement shares	Nowhere. You add it yourself	ITA s.53(1)(f)
Stock split	Pool unchanged, average per share falls	Broker notice	T4037, stock splits
Selling part of the holding	Pool down by the cost of shares sold, average per share unchanged	T5008	T4037, dispositions do not affect the ACB
Buying in a foreign currency	ACB fixed in Canadian dollars at the acquisition-date rate	Statement in the foreign currency	T4037, foreign currency

Notice the fourth row. The denied superficial loss is the one adjustment that appears on no slip, in no statement and in no broker’s system. If you do not write it down, the deduction the Act granted you simply evaporates.

Nine quarters of a dividend reinvestment plan, from the filing

A dividend reinvestment plan is where the averaging rule stops being theory. Every reinvestment is a purchase. Every purchase re-averages the pool. Over a few years a position you have not traded at all can accumulate dozens of small purchases at dozens of different prices, none of which you chose and all of which are yours to track.

Here is a real payer, with the dividends taken from the company’s own filing rather than from any data vendor. Royal Bank declared $1.76, $1.64, $1.64, $1.54, $1.54, $1.48, $1.48, $1.42 and $1.42 per common share over nine consecutive quarters, $13.92 in total, as reported on page 5 of its Q3 2026 Supplementary Financial Information. The same nine amounts appear against the nine ex-dividend dates in our own price capture, and the tool that builds this ledger asserts the filing and the capture agree before it draws anything. That check is the reason the table below can be trusted rather than merely presented.

The starting position: 100 shares bought at the July 24, 2024 close of $152.21, plus a $9.95 commission. The commission is part of the cost, so the pool opens at $15,230.95 and the average is $152.3095 a share rather than $152.21.

Two simplifications, stated plainly so the ledger is not mistaken for a statement. Each reinvestment here is priced at the closing price on that ex-dividend date, while a real plan prices on the payment date a few weeks later. And a brokerage-run plan usually buys whole shares and pays out the remainder in cash, rather than crediting fractions. Neither changes the arithmetic of the pool by a single step: cash arrives, shares are bought at a price, the pool rises by the cash and the average is recomputed.

Date	Dividend per share	Shares held before	Cash	Price	Shares bought	Shares held after	ACB pool	Average cost
2024-07-24 (purchase)	n/a	n/a	n/a	$152.21	100.0000	100.0000	$15,230.95	$152.3095
2024-07-25	$1.42	100.0000	$142.00	$151.52	0.9372	100.9372	$15,372.95	$152.3022
2024-10-24	$1.42	100.9372	$143.33	$171.20	0.8372	101.7744	$15,516.28	$152.4576
2025-01-27	$1.48	101.7744	$150.63	$176.19	0.8549	102.6293	$15,666.91	$152.6553
2025-04-24	$1.48	102.6293	$151.89	$163.04	0.9316	103.5609	$15,818.80	$152.7487
2025-07-24	$1.54	103.5609	$159.48	$180.07	0.8857	104.4466	$15,978.28	$152.9804
2025-10-27	$1.54	104.4466	$160.85	$207.45	0.7754	105.2219	$16,139.13	$153.3818
2026-01-26	$1.64	105.2219	$172.56	$229.56	0.7517	105.9737	$16,311.69	$153.9222
2026-04-23	$1.64	105.9737	$173.80	$239.56	0.7255	106.6991	$16,485.49	$154.5044
2026-07-27	$1.76	106.6991	$187.79	$296.11	0.6342	107.3333	$16,673.28	$155.3411
Totals	$13.92		$1,442.33		7.3333	107.3333	$16,673.28	$155.3411

Two things in the table repay a second look.

The average can fall. The first reinvestment bought at $151.52, below the $152.3095 the pool was carrying, and the average drops to $152.3022. A reinvestment made when the shares are cheap pulls the average down, exactly as an ordinary purchase would. Nothing about a reinvestment is special. It is a purchase you agreed to in advance.

The pool grew far more slowly than the position’s value. The average cost per share moved from $152.3095 to $155.3411 across nine quarters. That is what reinvestment does mechanically: each new share enters at the price of the day, and the average drifts toward it in proportion to how much of the position it represents. The compounding effect of those extra 7.3333 shares, each of which then earns dividends of its own, is the subject of our guide to compounding and why time beats timing.

The identity at the end of the ledger

Now sell. All 107.3333 shares go at the September 18, 2026 close of $284.45, less a $9.95 selling commission, for proceeds of $30,521.02.

Line	Tracked correctly	Never tracked
Proceeds, net of the $9.95 selling commission	$30,521.02	$30,521.02
Adjusted cost base	$16,673.28	$15,230.95
Capital gain reported	$13,847.74	$15,290.07
Gain overstated by		$1,442.33
Dividends the plan reinvested over the nine quarters		$1,442.33
Difference between the two		$0.0000

That is not an approximation. The amount by which you overstate the gain is the amount of dividends you already declared as income, to the cent, checked in code before the chart was drawn. It has to be. Every dollar the plan reinvested was taxed as a dividend in the year it was paid, and the Act then required that same dollar to be added to your cost base under section 53(1). Leave the addition out and the dollar is taxed a second time, as a capital gain, on the way out.

Half of $1,442.33 enters income as a taxable capital gain that was never owed. The tax on that is real money, and it is paid in exchange for not having kept a spreadsheet. Reinvestment plans are most common among Canadian dividend payers, the kind of holding people buy specifically to leave alone for a decade, which means the pool has usually drifted a long way from the purchase price by the time anyone thinks to check. Our ranked page of Canadian dividend stocks is full of exactly these positions.

Return of capital: the adjustment that runs downward

Everything above pushes the pool up. Subsection 53(2) is the mirror list, and return of capital is where most investors meet it.

Some distributions are not income at all. They are your own capital handed back, and because it was never taxed on the way out, it reduces what the holding cost you. Mutual fund trusts and many ETFs do this, and it turns up in box 42 of the T3 slip. T4037 describes the box directly:

> “Any amount reported in box 42, Amount resulting in cost base adjustment, of > the T3 slip represents a change in the capital balance of the mutual fund > trust identified on the slip.”

Ignore box 42 and your cost base stays too high, your eventual gain comes out too low, and you have understated your income. That is the opposite error to the DRIP one, and the CRA has a mechanism for the extreme case. Where enough return of capital arrives that the ACB of the units would be pushed below zero during the year, “the negative amount is deemed to be a capital gain in the year from a disposition of the property at that time”, and the ACB is then deemed to be nil. You are taxed on it at that point, without having sold anything.

That last mechanic matters for anyone holding a high-distribution fund for a long time in a taxable account. A fund returning capital year after year can grind the cost base down to nothing, and the gain arrives whether or not you were ready for it. Covered-call and high-yield products are the usual offenders, and the distribution breakdown is worth checking before you buy rather than at sale time: our ranked page of Canadian ETFs notes what each fund actually pays out.

A stock split changes the average and nothing else

Splits look alarming on a statement and are the easiest event on this page. T4037:

> “Generally, a stock split takes place if a company’s outstanding shares are > divided into a larger number of shares without changing the total market > value of the company’s holdings.”

The CRA’s own example: 100 shares valued at $60 each become, after a 2-for-1 split, 200 shares worth $30 each. The pool is untouched. The number of shares doubles, so the average cost per share halves. Nothing was disposed of, so nothing is taxable, and the split appears nowhere on your return.

The only work a split creates is bookkeeping. If your record is a list of purchase prices rather than a running pool, every historical entry has to be restated, and forgetting to do it leaves a cost base twice as large as it should be.

Foreign currency: two exchange rates, and only one of them is the one you remember

This is the trap that produces tax bills people are convinced are wrong.

A capital gain on a Canadian return is a Canadian dollar gain. T4037 requires three separate conversions, each at its own moment. You must convert:

> “the proceeds of disposition to Canadian dollars using the exchange rate in > effect at the time of the sale”

> “the ACB of the property to Canadian dollars using the exchange rate in > effect at the time the property was acquired”

> “the outlays and expenses to Canadian dollars using the exchange rate in > effect at the time they were incurred”

Three moments, three rates. Your cost base is locked in Canadian dollars on the day you bought, and it never moves again no matter what the currency does. On which rate to use, the guide says: “In general, the foreign currency amount should be converted using the Bank of Canada exchange rate in effect on the day of the transaction.” The CRA will also generally accept a rate from another source, provided it is “widely available”, “verifiable”, “published by an independent provider on an ongoing basis” and “recognized by the market”. The Bank of Canada’s daily exchange rates are free, permanent and never argued with, which makes them the sensible default.

What follows is not a quirk. Take a US-listed position worth exactly $20,000 USD on the day it was bought and exactly $20,000 USD on the day it was sold, September 18, 2026. In US dollars the investor made nothing at all, every time. The Bank of Canada series FXUSDCAD, 1,424 daily observations from January 4, 2021 to September 18, 2026, decides the Canadian answer. At the September 18, 2026 rate of 1.4002, the proceeds are $28,004.00 CAD in every row below.

Bought	Bank of Canada rate	ACB in Canadian dollars	US dollar gain	Canadian capital gain or loss
2021-01-04	1.2751	$25,502.00	$0.00	Gain of $2,502.00
2022-01-04	1.2708	$25,416.00	$0.00	Gain of $2,588.00
2023-01-03	1.3658	$27,316.00	$0.00	Gain of $688.00
2024-01-02	1.3316	$26,632.00	$0.00	Gain of $1,372.00
2025-01-02	1.4418	$28,836.00	$0.00	Loss of $832.00

Five identical investments, in the sense that matters to the investor, and five different Canadian tax outcomes ranging from a $2,588.00 gain to an $832.00 loss. The stock did nothing. The currency did all of it, and the Act taxes the result because your cost base was denominated in Canadian dollars from the moment you acquired the shares.

The range in the captured window is wider still. FXUSDCAD sat at 1.2040 on June 1, 2021 and at 1.4603 on February 3, 2025. Buying at the first and selling at the second, on a US dollar position that did not move at all, produces a $5,126.00 CAD capital gain, which is 21.29% of the cost base. Someone in that position pays real tax on an investment that made them nothing, and the only way to see it coming is to have recorded the acquisition-date rate at the time.

The practical rule is short. Every time you buy a foreign holding, write down the Bank of Canada rate that day along with the price. A statement in US dollars will never tell you your cost base, because your cost base is not a US dollar number.

Superficial losses: the add-back that survives, and the one that dies

Realise a loss and buy the same thing straight back, and the Act declines to give you the deduction. Section 54 defines a superficial loss as a loss “from the disposition of a particular property where (a) during the period that begins 30 days before and ends 30 days after the disposition, the taxpayer or a person affiliated with the taxpayer acquires a property (in this definition referred to as the ‘substituted property’) that is, or is identical to, the particular property, and (b) at the end of that period, the taxpayer or a person affiliated with the taxpayer owns or had a right to acquire the substituted property”.

The window is 61 calendar days: 30 before, the day of the sale itself, and 30 after. Affiliated persons include your spouse or common-law partner and your own registered plans, which is where most accidental breaches happen. The full list, the spouse trap and the way the window is counted are worked through in our research piece on the superficial loss rule in Canada. Then section 40 does the denying: under s.40(2)(g)(i), the loss is nil “to the extent that it is a superficial loss”.

That sounds like a penalty. In one of the three ways this plays out, it is not a penalty at all. In the other two, it is permanent.

The example: 200 shares bought at $50.00 with a $9.95 commission, so the cost base is $10,009.95. They fall to $30.00 and are sold, netting $5,990.05 after a $9.95 selling commission. The capital loss is $4,019.90. The investor is an Ontario resident with $90,000 of taxable income, which puts them in the federal 20.50% bracket and the Ontario 9.15% bracket for a combined marginal rate of 29.65%. The shares later recover and are sold for good at $55.00.

Path 1: rebuy in the same taxable account

The investor buys 200 shares back at $30.00 inside the 61 days, in the same non-registered account. The loss is denied by s.40(2)(g)(i). Then section 53(1)(f) adds it to the replacement shares, because the add-back applies “where the property is substituted property (within the meaning assigned by paragraph (a) of the definition superficial loss in section 54)”. The CRA states the same thing in plainer language in T4037: a superficial loss cannot be deducted in the year, but the person who acquires the substituted property can usually add the amount of the superficial loss to its adjusted cost base, which decreases the capital gain or increases the capital loss when those shares are sold.

So the new cost base is $6,000.00 for the shares, plus the $9.95 commission, plus the $4,019.90 that was denied: $10,029.85.

The recovery sale of 200 shares at $55.00, less $9.95, brings in $10,990.05. Against a cost base of $10,029.85 that is a capital gain of $960.20, and at the example rate the tax is $142.35.

Now run the same trades with the rebuy made outside the window, so the loss is allowed. The replacement shares carry their own cost with no add-back, the recovery sale produces a gain of $4,980.10, the allowed loss of $4,019.90 is applied against it, and the net is $960.20. The tax is $142.35.

Identical to the cent. The deduction was not taken away. It was moved from one sale to the next, sitting inside the cost base of the replacement shares in the meantime. Path 1 costs nothing but time.

Paths 2 and 3: the replacement shares land inside a plan

Change one thing. The investor sells at a loss in the taxable account and buys the replacement shares inside their TFSA or RRSP within the window. The plan is an affiliated person, so the loss is still superficial and still denied. Section 53(1)(f) still performs the add-back, and that is the problem: the $4,019.90 lands on the cost base of shares held inside a registered plan, where cost base has no tax effect whatsoever. There is no Schedule 3 for a TFSA. The deduction is not deferred. It has nowhere to go.

The third version reaches the same place by a shorter route. Contribute the losing shares to the plan in kind rather than selling them on the market, and s.40(2)(g)(iv) makes the loss nil directly, on a disposition of property to a trust governed by, among others, “a FHSA, a registered disability savings plan, a registered retirement income fund or a TFSA, under which the taxpayer is a beneficiary”, or a trust governed by an RRSP under which the taxpayer or their spouse is an annuitant.

The permanent cost is the deduction, valued at the investor’s own rate: $4,019.90 x 0.5 x 29.65% = $595.95.

Path	What happens to the $4,019.90 loss	Tax on the recovery sale	Permanent cost
Loss allowed (rebuy outside the window)	Deducted against the later gain of $4,980.10, net $960.20	$142.35	$0.00
Rebuy in the same taxable account	Denied, then added to the new ACB of $10,029.85	$142.35	$0.00
Rebuy inside a TFSA or RRSP, or contribute in kind	Added to a cost base inside a plan, where it does nothing, or denied outright	n/a	$595.95

The lesson is not “never trip the superficial loss rule”. Tripping it inside one taxable account is free. The lesson is that the account the replacement shares land in decides whether the deduction is deferred or destroyed, and the move that destroys it, buying the shares back in the tax-free account, is the one that feels most sensible to someone who has just taken a loss. What a TFSA does well, and what it cannot do, is set out in our guide to how a TFSA works; the equivalent for retirement money is in our guide to how an RRSP works.

One timing note, and one only, because it belongs to a dated piece rather than to this page. A loss realised late in the year has to settle in order to count for that year, and the effective deadline is earlier than December 31. Our research on tax-loss selling in Canada carries the current working and the three-year carryback that follows from it.

Keeping the pool yourself

Nothing in this guide is difficult. All of it is record-keeping, and the record has to be yours because no institution holds all the inputs.

Your broker knows the purchases made in the account it runs. It does not know about the same shares at a second broker, and the pool spans both. It does not adjust for a superficial loss, because nothing in its system knows the loss was denied or where the replacement shares went. It may or may not process a box 42 return of capital against book value. It cannot know the Bank of Canada rate you should have recorded on a US purchase, because it settled that trade in US dollars and never had to think in Canadian ones.

So the minimum record, per holding, is a single running list: every purchase with its date, share count, price and commission; every reinvestment; every return of capital; every split; every superficial loss add-back; and for foreign holdings, the exchange rate on the day of each acquisition. Keep the pool and the average updated after each entry. A column of purchase prices is not enough, because the average is the thing the tax is measured against and it changes on entries you did not initiate.

The first time most people realise this is the year they sell something they have held through a reinvestment plan for a decade, open the statement, and find that the number they need was never anywhere.

Questions people actually ask

My broker shows a book value. Is that my adjusted cost base? Only by coincidence. It is the broker’s figure for the account it can see, and it is a starting point the CRA expects you to adjust. It cannot include holdings at another institution, a denied superficial loss, or anything the broker was not told.

I own the same stock in my TFSA and my cash account. Does the TFSA affect my average? No. There is no adjusted cost base inside a TFSA, RRSP, FHSA, RRIF or RESP, and nothing in those accounts appears on Schedule 3. Your pool is built only from non-registered holdings. The registered account matters in one place: it counts as an affiliated person for the superficial loss rule, which is how buying replacement shares there destroys the deduction.

Can I choose which shares I sold to control the gain? No. Canada has no lot selection of any kind. Identical shares form one pool at one average, and every sale is measured against that average.

Does selling half my position change my cost per share? No. T4037 is explicit that dispositions of identical properties do not affect the ACB. The pool falls by the cost of the shares that left, at the average, and the average per share on what remains is exactly what it was.

Do reinvested dividends get taxed twice? Not if you track them. They are taxed once as dividend income in the year they are paid, and that same amount is added to your cost base under s.53(1) so it is not taxed again on the sale. They are taxed twice only when the add-back is skipped, which is what the $1,442.33 identity in the ledger above demonstrates.

My US stock is worth what I paid for it in US dollars. How can there be a gain? Because the gain is computed in Canadian dollars, with your cost base converted at the rate when you acquired the shares and your proceeds at the rate when you sold them. In the five worked examples above, a position flat in US dollars produced Canadian outcomes from a $2,588.00 gain to an $832.00 loss.

Does a stock split create a taxable event? No. Nothing is disposed of. The pool is unchanged and the average cost per share falls in proportion to the new share count, which in the CRA’s own 2-for-1 example turns 100 shares at $60 into 200 shares at $30.

What if a fund’s return of capital pushes my cost base below zero? The negative amount is deemed to be a capital gain in that year from a disposition at that time, and the ACB is then deemed to be nil. You are taxed on it without having sold anything.

One scope note

The tax arithmetic on this page uses Ontario rates, because a worked example needs a province. The federal half of every calculation is identical everywhere in Canada and the mechanics of the cost base are federal, but the provincial rate applied to the taxable half of a gain is not, and Quebec administers its own return. Rates, thresholds and the rules themselves change. This is general tax information rather than tax advice, so confirm anything that turns on your own numbers with the Canada Revenue Agency or a qualified tax professional before you act on it.

Where to go next

Once it is clear that the pool is yours to keep, the next question is where to keep it. Our Adjusted Cost Base Tracker holds the running total across purchases, reinvestments and adjustments, which is the record this whole guide argues you need and no broker will build for you.

When the pool eventually meets a sale, the figure it produces becomes a tax bill at your own rate rather than the Ontario example used here, and our capital gains tax calculator applies the current federal and provincial ladders to a gain you are actually considering.

Cost base is the fourth thing a Canadian investor has to get right, after the account, the purchase and the tax treatment of what the holding pays. All of them sit in order in our investing course, which starts from what a share is and works down to the point where a page like this one reads as obvious rather than as bad news.