Wash Sale Calculator

The tool follows the IRS wash-sale principle: when substantially identical securities are repurchased within 30 days before or after a loss sale, the loss attributable to the replacement shares is disallowed and is added to the basis of those replacement shares.

Computation: calculate per-share realized loss (original cost per share minus sell price, floored at zero), determine how many replacement shares fall within the 30-day window, multiply per-share loss by the number of replacement shares that can absorb the loss, and allocate that disallowed loss to the replacement shares by adding the disallowed amount per share to their purchase cost.

Security and quality statements: this tool follows secure development and data-handling recommendations and quality management guidance; see NIST and ISO references in citations. Outputs depend on user input accuracy and rounding rules.

Enter the sold-share cost, sell price, quantity, replacement lot quantities and costs, and days between sale and repurchase. Use the multi-lot FIFO method for typical brokerage-like allocation.

This calculator gives an estimate of disallowed loss and adjusted basis. Confirm figures with brokerage statements and consult a tax professional before filing.

Example 1: Sell 100 shares at a $10 loss per share and buy 50 replacement shares within 30 days. Disallowed loss = $10 × 50 = $500. If the 50 replacement shares cost $95 each, the adjusted basis per replacement share = 95 + (500 / 50) = $105.

Example 2: Sell 100 shares at a $2 loss per share and buy 120 replacement shares within 30 days across multiple lots. Applicable replacement shares = min(100, 120) = 100, disallowed loss = $2 × 100 = $200. The $200 is allocated across the replacement shares' basis calculation as specified.