Cost Basis Calculator

Cost basis is what your shares cost you once every adjustment since the purchase has been applied, and it is the figure a capital gain is measured against. One action takes the purchase and commission, the dividends you reinvested, any return of capital received, a disallowed wash sale loss and a stock split, and returns the adjusted basis and the basis per share. The other takes up to four lots and a sale, and works the gain under FIFO, LIFO or a specific lot chosen for its cost, showing all four side by side because the same sale gives a different answer under each. Nothing is looked up here: every price, dividend and split ratio comes from your own records. It is arithmetic rather than tax advice, and it does not decide whether a wash sale applied or whether a gain is short or long term.

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Fees paid to buy are part of the basis, so they raise it.
Reinvested dividends were taxed when paid, so every dollar of them is basis. Leaving them out is the most common way a basis comes out too low.
The total extra shares the plan bought for you, fractions included.
Nondividend distributions, box 3 of a 1099-DIV. These are not income; they come off the basis.
A loss disallowed under the wash sale rule is added to the basis of the shares you bought back. You have to work out whether the rule applied.
For a 2-for-1 split enter 2 here and 1 below. For a 1-for-10 reverse split enter 1 here and 10 below.
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The adjusted basis per share for that lot, commission included.
Selling costs come off the proceeds, so they reduce the gain.
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