US Capital Gains Tax Calculator

How this calculator works

Long-term ordinary-asset gains stack above your other ordinary taxable income and can cross the 0%, 15% and 20% thresholds. The preferential calculation is compared with ordinary-income tax on the combined amount, using the lower result within this simplified scope. Short-term gains use the ordinary-income increment. A separate 3.8% NIIT estimate uses entered MAGI, assuming this gain is the only net investment income. Capital losses must already be netted and any relevant exclusion applied before you enter the gain.

Formula and rules

Long-term gain slices fill the remaining 0% and 15% bands, with the rest at 20%, capped by the ordinary-tax increment. Short-term tax = tax(other income + gain) − tax(other income). NIIT = 3.8% × min(gain, max(0, entered MAGI − filing threshold)).

Assumptions and limitations

Ordinary capital assets only; no qualified dividends, collectibles, depreciation recapture, home-sale eligibility, AMT, other investment income or state taxes. Loss netting and exclusions are supplied in the entered gain. MAGI is not inferred from taxable income. No filing or timing advice is provided.

Worked example

For a Single filer with $40,000 other ordinary taxable income and a $10,000 long-term gain, $9,450 fills the 2026 zero-rate band and $550 is in the 15% slice. The simplified gain tax is $82.50; at $66,100 MAGI the model adds no NIIT.

Estimated federal tax attributable to the gain

$82.50

Capital-gain income tax

$82.50

NIIT on the gain under entered MAGI

$0.00

Long-term gain in the 0% slice

$9,450.00

Official sources and review

Reviewed against the sources below on 2026-10-06. Rates are held in versioned rule modules. Versioned rules, official source review and year-specific calculation tests.

• IRS Publication 505 (2026) ↗

  2026 ordinary-income rate schedules, standard deductions and capital-gain worksheet thresholds.

• IRS: Net Investment Income Tax ↗

  3.8% NIIT uses MAGI thresholds and net investment income; not identical to capital-gain brackets.

Common questions