Wash sale calculator: is your loss disallowed?
Enter your trades, buys and sells in any order. The calculator finds every sale at a loss with a purchase of the same ticker in the 30 days before or after it, works out how much of the loss is disallowed and which shares it moves into, and tells you the first day you can buy back. It runs in your browser: your trades are not sent anywhere or saved.
One trade per line: date, ticker, buy or sell, shares, price per share. Columns separated by tabs (as copied from a spreadsheet), commas or semicolons. Dates as 2026-03-14 or 03/14/2026. A header line is skipped.
An estimate, not tax advice. It matches exact tickers in the trades you enter; see the questions below for what it does not cover.
How the wash sale rule works
A loss on a sale of stock is disallowed when you buy the same or a substantially identical security within 30 days before or after the sale: a 61-day window around the sale date. If you bought back fewer shares than you sold, only the loss on that number of shares is disallowed.
The loss is not gone. It is added to the cost basis of the replacement shares, so it comes back when you sell them. The rule looks at every account you own, at every broker, which is why no single 1099-B can catch a wash sale across two brokers.
Disallowed loss = $250, and your basis in the new shares is $800 + $250 = $1,050. Sell them later for $900 and you report a $150 loss: the $250 comes back, less the $100 the shares gained.
The XYZ trades in the example above are this case.
How does the wash sale rule work?
If you sell a stock at a loss and buy the same or a substantially identical security within 30 days before or after the sale, you cannot deduct the loss now (IRC section 1091). The window is 61 days: the 30 days before, the day of the sale and the 30 days after. If you bought back fewer shares than you sold, only the loss on that number of shares is disallowed.
Where does the disallowed loss go?
Into the cost basis of the replacement shares. It comes back when you sell those shares, as a smaller gain or a bigger loss, unless that sale is a wash sale too. The holding period of the shares you sold also carries over to the replacement shares; this calculator does not extend it.
Does it apply across brokers and accounts?
Yes. A purchase in any account you own counts, and so does one by your spouse. A replacement bought in an IRA disallows the loss for good, without adding it to any basis (Rev. Rul. 2008-5). Enter the trades from all your taxable accounts; purchases in an IRA cannot be modelled here.
What does the calculator match?
The same ticker. It does not detect a substantially identical security under another ticker, such as options on the stock; check those yourself. Each share bought can replace only one sale, earliest purchase first, and the shares a sale disposes of are never their own replacement.
Does the rule apply to crypto?
Not in 2026. Section 1091 covers stock and securities, and the IRS treats crypto as property (Notice 2014-21). Known coin tickers such as BTC and ETH are left out of the check.
What about commissions?
Add buy commissions to the buy price and subtract sell commissions from the sell price. The calculator then counts them in the cost and in the proceeds.
Is the same engine used in the Zyvo app?
Yes. It is the app's own wash sale code, the check behind its US tax estimate and its Form 8949 export, copied unchanged and run on the trades you type in instead of your synced brokers.
Is what I enter saved?
No. The calculation runs in your browser, and your trades are not sent anywhere or saved. Zyvo counts visits to this page and how many trades were checked, never what they were.
Is this tax advice?
No. It is an estimate to help you plan and to check your statements. Your 1099-B forms and a tax professional have the final word.
Sources: IRS Publication 550 (Wash Sales) · 26 U.S.C. § 1091 · IRS Notice 2014-21