Wash Sale Calculator & Checker (30-Day Rule)

Opens on Publication 550's example: 100 shares sold at a $1,000 loss, 75 bought in the 30 days before.

Date	Symbol	Buy / sell	Shares	Price ($)	Remove

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Losses on 1 sale

$750.00 of $1,000.00 disallowed

Deductible now: $250.00. The disallowed loss moves into the basis of the shares bought; $750.00 of it is in shares still held.

M sold 2025-01-03 at a $1,000.00 loss: $750.00 disallowed, added to 50 shares bought 2024-12-13 (+$500.00) and 25 shares bought 2024-12-20 (+$250.00).

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The math: disallowed = the loss on the shares sold, up to the shares bought within 30 days either side, matched in the order bought

How the 30-day rule works

A loss is disallowed when the same stock is bought within 30 days before or after the sale; it moves into the new shares' basis.

The rule in Publication 550's words

"A wash sale occurs when you sell or trade stock or securities at a loss and within 30 days before or after the sale you: buy substantially identical stock or securities, acquire substantially identical stock or securities in a fully taxable trade, acquire a contract or option to buy substantially identical stock or securities, or acquire substantially identical stock for your individual retirement arrangement (IRA) or Roth IRA." The disallowed loss is added to the cost of the new shares, except in the IRA case, and their holding period includes the old shares'. Where you buy more or fewer shares than you sold, "match the shares bought in the same order that you bought them, beginning with the first shares bought" (IRS Publication 550, for 2025 returns, read 25 October 2026).

The year-end wash sale

Sell at a loss in December, buy back in January, and the loss leaves that year's return.

An example in dates

Sell 100 shares at a $2,000 loss on Monday 14 December 2026 to harvest it, and buy them back on Tuesday 5 January 2027: the buy is 22 days after the sale, inside the window, so the $2,000 isn't deductible for 2026. It is added to the January shares' basis and deducted when they are sold. Waiting until Thursday 14 January 2027, 31 days after, keeps the 2026 loss.

What a checker can't see

Buys in your other accounts, your IRA, or by your spouse count too; brokers report wash sales within one account.

Accounts, options and the exceptions

Publication 550 counts purchases for your IRA or Roth IRA (the loss is then lost, not deferred), and purchases by your spouse or a corporation you control. Options to buy the stock count; commodity futures and foreign currencies are outside the rule. A trader with a timely section 475(f) mark-to-market election isn't subject to it for trading securities (IRS Topic no. 429); see the trader tax status checker. This page is arithmetic over the trades you enter, not tax advice.

Method and privacy

Method: Shares are sold oldest first (FIFO). A loss is disallowed to the extent shares of the same symbol are bought within 30 days before or after the sale, matched in the order bought with each share replacing once, as IRS Publication 550 (for 2025 returns) describes; the disallowed loss is added to those shares' basis. Purchases in other accounts, an IRA or by a spouse, and options or other substantially identical securities, aren't seen. Not tax advice.

Calculations run entirely in your browser — nothing you type is uploaded. Your last numbers stay in this browser so you can pick up where you left off; Forget them clears them. A link with your numbers carries them after the # sign, which browsers do not send to servers, and the page takes them out of the address before any analytics loads. Copy and download actions save your calculation locally. The site may record coarse tool actions under its privacy policy, without inputs, results, file contents or filenames.

Common questions

What is the wash sale rule?

If you sell stock or securities at a loss and buy substantially identical ones within 30 days before or after the sale, you can't deduct the loss then. It is added to the cost basis of the new shares, so it comes back when you sell them, and their holding period includes the old shares'. IRS Publication 550 sets this out under Wash Sales.

Does the wash sale rule count buys before the sale?

Yes. The window runs from 30 days before the sale to 30 days after it, 61 days in all. In Publication 550's example, 75 shares bought in the 30 days before a sale of 100 shares at a $1,000 loss disallow $750 of it, and the other $250 stays deductible.

What if I buy back fewer shares than I sold?

Only that many shares' loss is disallowed. The shares bought are matched with the shares sold in the order you bought them, and each block takes its part of the loss into its basis: in the IRS example, $500 goes to 50 shares and $250 to 25.

Can a wash sale carry a loss into next year?

Yes. A loss in late December with a buy back in early January is disallowed for that year: it moves into the basis of the January shares and is deducted when those are sold. The checker flags it.

Does buying in my IRA trigger a wash sale?

Yes. Publication 550 counts substantially identical stock bought for your IRA or Roth IRA, and in that case the loss is not added to any basis, so it is lost. Buys by your spouse or a corporation you control count too. A broker reports wash sales within one account, so check across accounts yourself.

Does the wash sale rule apply to futures?

No. Publication 550 says the wash sale rules do not apply to losses from sales or trades of commodity futures contracts and foreign currencies. They do apply to contracts and options to buy or sell stock or securities.

Does the wash sale rule apply to day traders?

Yes, unless you have trader tax status and made a timely section 475(f) mark-to-market election: then, IRS Topic 429 says, the wash sale rules and the capital loss limits don't apply to your trading securities. Without the election both still apply.

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