Free Capital Gains Tax Calculator — Tax-Lot Selection Strategy

Last updated: April 17, 2026

MoneyMath's capital gains tax calculator estimates 2026 short-term and long-term federal tax, NIIT, tax-lot selection, loss harvesting, and whether waiting for long-term rates is worth it.

Free to useRuns in your browserSource-backed assumptions

Free capital gains tax calculator with tax-lot selection strategy. Choose which shares to sell, harvest losses to offset gains, see the wash sale trap, and decide if waiting one more month for long-term rates is worth it.

Use the Capital Gains Tax Calculator to compare realistic scenarios before making a money, health, or planning decision.

Adjust the inputs and review the result breakdown so you can see which assumptions matter most.

How to use this calculator

Step 1Enter your starting information. Add the core inputs requested by the Capital Gains Tax Calculator, such as amounts, dates, rates, income, weight, or other scenario details.
Step 2Review the calculated result. Read the headline answer first, then scan the supporting breakdown, chart, or comparison table.
Step 3Compare another scenario. Change one input at a time to understand what drives the result and which option is most realistic.

Formula, Sources & Assumptions

Formula

Capital gains tax = applicable federal gain rate plus NIIT when income exceeds the NIIT threshold, after tax-lot and loss-harvesting assumptions.

Assumptions

Federal rates use 2026 long-term capital gains and ordinary income thresholds.
State capital gains taxes are not included.
The calculator assumes simplified taxable income layering and does not replace tax-lot instructions to a broker.

Sources

IRS 2026 tax inflation adjustmentsFederal brackets, standard deduction, and indexed tax items.