**The information below has not been verified for tax year 2023 as IRS Pub. 550 has not yet been released by the IRS.**
A stock split affects your number of shares and your basis in each share. To get your new basis per share, divide your total adjusted basis in the old stock by the number of shares you own after the split. If all shares are sold together, this will not affect your profit or loss because you enter the total purchase price and the total sale price to calculate your profit (loss).
According to the tax authoritiesPublication 550 Income and expenses from investments (including capital gains and losses), side 35:
Stocks and bonds
The basis of any stock or bond you own is usually the purchase price plus purchase costs, such as commissions and registration or transfer fees. If you acquired stocks or bonds other than through purchase, your basis is generally determined based on the fair market value or the previous owner's adjusted basis, as previously discussed underBasis other than costs.
The inventory base must be adjusted for certain events that occur after the purchase. For example, if you receive more shares from non-taxable stock dividends or stock splits, you must reduce the basis of your original shares. Even if you receive non-dividend distributions, you must reduce your basis (discussed in Chapter 1). These payments constitute, up to the amount of your basis, a non-taxable capital income.
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