A plain split isn’t a disposition
In a conventional stock split, you receive additional shares in proportion to what you hold — a 2-for-1 split doubles your share count. You haven’t sold anything, so there’s no capital gain or loss and no tax event. Your total ACB is unchanged.
Reverse splits
A reverse split (e.g. 1-for-10) works the same way in the other direction: fewer shares, higher per-share ACB, unchanged total. Watch for fractional shares paid out in cash — that small cash-in-lieu payment is a disposition and can create a tiny gain or loss you need to report.
Splits vs. stock dividends
A stock dividend can look like a split but is treated differently: it may carry an income inclusion and add to your ACB by the amount included. Read the corporate action carefully — “you got more shares” doesn’t always mean “nothing to report.”