Wash Sale Calculator
Estimate the disallowed loss and replacement basis for one taxable stock lot and one replacement purchase. The inputs below are a hypothetical example, not your transaction history.
Assume the replacement is substantially identical, separate from the shares sold, and remains held. Other purchases and accounts can change the answer. This is a US educational estimate, not a tax return calculation.
Wash sale adjustment in this scenario
Inclusive window: 2024-12-16 through 2025-02-14. Replacement: 10 days after sale (inside the window).
- Basis of shares sold
- $15,000.00
- Sale proceeds
- $12,000.00
- Realized gain / loss
- -$3,000.00
- Matched replacement shares
- 100
- Disallowed loss
- $3,000.00
- Gain / loss after this adjustment
- $0.00
- Total replacement-lot basis
- $15,500.00
- Remaining original-lot basis
- $0.00
Negative amounts are losses. The remaining loss is not necessarily immediately deductible: capital-loss limits and other rules still apply. Total replacement basis aggregates the lot; if only some shares match, track the adjustment on those shares rather than spreading it across unmatched shares.
How the calculation works
Sold basis equals shares sold × adjusted basis per share. Realized gain or loss equals sale proceeds minus that sold basis. Unsold original shares keep their own basis.
For a loss and a qualifying replacement within the inclusive 61-day window, matched shares are the smaller of shares sold and replacement shares. Disallowed loss equals matched shares × loss per share. In this taxable-account model, add it to the replacement purchase cost and add it back to the negative realized loss.
Example: sell 100 shares with $150 basis per share at $120, then buy 40 replacement shares at $125 within the window. The $3,000 realized loss has $1,200 disallowed; the remaining loss is $1,800 before other tax limits. Replacement basis is $5,000 + $1,200 = $6,200.
What a single-lot estimate cannot determine
Multiple purchases require share matching in purchase order. Multiple wash sales require transaction-level basis tracking, not simple netting. Reinvestments, spouse accounts, retirement accounts, and options can require additional analysis. The tool does not import broker records, classify substantially identical securities, compute holding periods, or calculate a tax bill.
For qualifying taxable replacements, the old holding period carries over. An IRA replacement has a different basis consequence. Check IRS Publication 550, Wash Sales and Revenue Ruling 2008-5, and consult a tax professional for your transactions.
Wash sale questions
What does this calculator assume?
One original taxable-account stock lot, one sale, and one separate replacement purchase of substantially identical stock that remains held. It excludes other lots, accounts, fees, prior basis adjustments, options, short sales, and special tax elections. It cannot decide whether two securities are substantially identical.
Does waiting 31 days after a sale rule out a wash sale?
Not by itself. Qualifying purchases in the 30 days before the sale also matter. A purchase exactly 30 days before or after is inside the window. Review all relevant accounts and reinvestments.
What if fewer replacement shares were purchased?
Only matching shares receive the adjustment in this simplified model. For a $30 per-share loss on 100 sold shares and 40 replacement shares, $1,200 is disallowed and $1,800 remains a loss before other tax limits.
Is an IRA replacement treated the same way?
No. A taxable-account loss followed by a qualifying IRA or Roth IRA purchase can be disallowed without increasing the IRA basis. This calculator models taxable replacement shares only; do not use its basis result for IRA replacements.
Does a cash dividend itself trigger a replacement purchase?
A cash dividend alone is not a purchase. Dividend reinvestment can buy replacement shares. Include those transactions when checking the window.
Capital gains tax calculator is a separate estimate; reconcile every tool with the rules and records that apply to your account.
Related Tools
Capital Gains Tax Calculator
Estimate the tax liability on your investment profits.
Capital Gains Tax Lot Optimizer
Optimize your investment tax liability by comparing FIFO, LIFO, HIFO, and tax-loss harvesting strategies. Upload trade history, track cost basis, and find the optimal lots to sell.