Wash Sale Calculator 2026 β Disallowed Loss & Adjusted Basis
Determine if your trade triggered a wash sale. Calculate the disallowed loss, adjusted cost basis of replacement shares, and remaining deductible loss.
Original Sale (at a Loss)
Repurchase (within 30-day window)
Step-by-Step Basis Adjustment
How the Wash Sale Rule Works
The wash sale rule (IRS Code Section 1091) prevents you from claiming a tax loss if you buy back the same or substantially identical security within 30 days before or after the sale. The 61-day window runs from 30 days before the sale through 30 days after the sale.
If the wash sale rule applies, the disallowed loss is not permanent β it is added to the cost basis of your replacement shares. This defers the loss until you eventually sell the replacement shares, at which point the adjusted basis results in a larger deductible loss (or smaller gain).
The Formula
Total Loss = Loss per Share Γ Shares Sold
Disallowed Ratio = Repurchased Shares / Sold Shares (max 1.0)
Disallowed Loss = Total Loss Γ Disallowed Ratio
Adjusted Basis = Repurchase Price + (Disallowed Loss / Repurchased Shares)
Deductible Loss = Total Loss β Disallowed Loss
Example
Total loss: 100 Γ ($38 β $50) = β$1,200
Wash sale triggered (12 days within 30-day window)
Disallowed loss: $1,200 (100% repurchased)
Adjusted basis of new shares: $40 + ($1,200 / 100) = $52 per share
Deductible loss this year: $0 (fully disallowed, deferred to future sale)
Multiple Lot Wash Sale Tracker
Analyze up to 5 sell/buy pairs β identify which trigger wash sales and calculate aggregate adjusted basis
Track multiple sell/repurchase pairs. The calculator identifies which trigger wash sales and aggregates your disallowed losses and adjusted bases.
| # | Symbol | Sell Date | Loss | Wash Sale? | Disallowed | Adj. Basis/Share | Deductible |
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