Stock Capital Gains Tax Calculator

Every capital gains calculation starts with one subtraction:

$G = \text{Proceeds} - \text{Cost basis}$

• Proceeds — shares $\times$ sale price, less selling commissions and fees
• Cost basis — shares $\times$ purchase price, plus buying commissions, adjusted for splits, reinvested dividends and any wash-sale disallowance

Tax is then the gain times whatever rate applies to it:

$T = G \times \text{rate}$

The rate is the part no calculator can supply. Almost every jurisdiction distinguishes gains on assets held a short time from gains on assets held longer, and the thresholds, the rates, the bands and the treatment of losses all differ by country and change from year to year. Frequent trading may also be classified differently from investing.

So the useful division of labour is this: the arithmetic below — basis, gain, netting, adjusted basis — is identical everywhere and is what this page computes. The rate is an input you supply from your own current rules, or from a qualified tax professional. Nothing here is tax advice.

The netting order

Gains and losses are combined within each holding-period category first, then across:

1. Net short-term: $\text{ST gains} - \text{ST losses}$
2. Net long-term: $\text{LT gains} - \text{LT losses}$
3. If one is positive and the other negative, offset them

A remaining net loss may be deductible against ordinary income up to a limit and carried forward — but the limit, the carry-forward period and whether it applies at all are jurisdiction-specific.

Basis when lots differ

Selling part of a position requires identifying which shares went. Specific identification uses the chosen lot's basis; FIFO uses the oldest; average cost is permitted for some assets in some places. The method changes $G$, sometimes dramatically.

Wash sales

Where the rule exists, selling at a loss and repurchasing a substantially identical security inside the window disallows the loss and adds it to the basis of the replacement:

$\text{New basis} = \text{Repurchase cost} + \text{Disallowed loss}$

The loss is deferred, not destroyed — it reappears when the replacement shares are sold.

Trading costs

$\text{Net} = G - \text{commissions} - \text{fees}$

Commissions belong in the basis and proceeds, not deducted separately afterwards.

• Forgetting commissions in the basis: buying costs raise the basis, selling costs reduce proceeds. Both lower the gain, and both are frequently omitted.
• Ignoring reinvested dividends: each reinvestment is a purchase with its own basis. Leaving them out inflates the gain and taxes the same money twice.
• Netting across categories first: short-term nets against short-term and long-term against long-term before the two are combined. The order changes the result.
• Assuming a loss is deductible immediately: a repurchase inside the wash-sale window defers it into the new basis.
• Applying one rate to a whole year of trading: gains are usually taxed by category, and often by band. A single blended percentage is an estimate at best.
• Using last year's rates: bands and thresholds are revised regularly. Always confirm the current figures for your jurisdiction.