Wash Sale Calculator

About this calculator

The IRS wash sale rule (Internal Revenue Code Section 1091) disallows a tax deduction for a capital loss if you buy the same or a 'substantially identical' security within a 61-day window: 30 days before the sale, the day of the sale, or 30 days after. It exists to stop investors from selling a losing position purely to claim a tax deduction while immediately buying it back and keeping their market position unchanged.

When the rule is triggered, the disallowed loss is not simply lost — it is added to the cost basis of the newly repurchased shares, which reduces your taxable gain (or increases your deductible loss) when you eventually sell those replacement shares for good. The portion of your original loss that falls outside the repurchase, if any, remains an allowed loss you can deduct right away.

Investors and tax preparers run this calculation especially during tax-loss harvesting season at year-end, when it's common to sell a losing stock or fund for the tax benefit while wanting to stay invested in a similar position — this calculator shows exactly how much of the loss the wash sale rule disallows and what your adjusted cost basis becomes.