Adjusted Cost Base (ACB)
Adjusted cost base (ACB) is the amount the CRA uses to calculate the capital gain or loss when you sell a capital property such as shares or real estate. It starts with what you originally paid, adds costs like commissions and capital improvements along the way, and when you own several identical units of the same property — shares bought at different times, for example — the ACB is averaged across every unit you hold rather than tracked lot by lot. Confirming the ACB carefully, rather than working from the original purchase price alone, is what determines the taxable gain when you eventually sell, and it matters most on assets held for years where records can go missing. Our capital gains tax guide and capital gains tax calculator both start from the ACB.
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