When you buy a stock or a mutual fund, you do so in hopes of making a profit. That is why it is so important to keep careful track of not only how much you paid for that security but any income it generates while you hold it. All of those factors go into your cost basis, which in turn helps you determine your true profit.
Computing your capital gain is important, since an inaccurate figure could cause you to either overpay or underpay your taxes. If you overstate your cost basis, you will pay too little in capital gains taxes, and that could invite some unwanted attention from Canada Revenue Agency. If you understate your cost basis, you will pay too much in capital gains taxes, cutting into your profit and leaving you with less money in your pocket.
Understanding Your Cost Basis
Many investors assume that the cost basis of a stock or mutual fund simply consists of the amount they paid, but in fact it is a bit more complicated than that. Many stocks and mutual funds pay dividends along the way, and those dividends are considered taxable income. When you hold a dividend-paying stock or mutual fund, you should receive a T3 or a T5 form each year showing exactly how much you received. You must then include that amount on your tax return, and pay the applicable taxes on that money.
If you fail to factor in those dividend payments, you risk understating your cost basis and paying taxes twice on the same money. When you receive a T3 or a T5 form, you should immediately add the amount shown to the amount you paid for the stock or mutual fund. Continue to add those dividend payments to your cost basis each year, since you have already paid taxes on those amounts. This is assuming you are not receiving cash for the dividends and they are just added back into the investment
Computing Your Capital Gain
The cost basis of your stock or mutual fund consists of the amount you paid, plus any brokerage commission, along with those quarterly or annual dividend payments. Once you have added up all those amounts and determined your true cost basis, it is time to compute your capital gain.
When you sell a stock or mutual fund, you should receive a T5018 form, which shows the amount of proceeds you received (some forms do show the cost and/or adjusted cost base too). Once you know your cost basis, computing your capital gain is as simple as subtracting that cost basis from the gross proceeds.
Once you know the amount of the capital gain, you can simply include it when you file your taxes. If you use tax preparation software to prepare your return, all you need to do is answer the questions about capital gains and use them to see the impact of that gain on your total tax bill.