Marlecourt
Investing

After-Tax Return Calculator

Estimate after-tax return by applying a user-supplied estimated tax rate to positive modeled pretax gain. This calculator performs arithmetic with the rate you enter. It does not determine your legally applicable tax rate.

Must be greater than zero.

Simple return over the modeled period (−100% to 1000%). Not annualized here.

Arithmetic assumption only (0–100%). Applies only to positive modeled gain.

Your results will appear here

Enter your assumptions and calculate to see the estimated result and supporting details.

How this calculator works

Enter investment amount, pretax return for the modeled period, and a user-supplied estimated tax rate (0–100%).

Results show pretax and after-tax gain or loss, estimated tax on positive gain, ending value, and tax drag.

Formula / methodology

pretax gain = investment × pretax return
estimated tax = max(pretax gain, 0) × tax rate
after-tax gain = pretax gain − estimated tax
after-tax return = after-tax gain ÷ investment
  • Losses produce $0 estimated tax — no invented tax benefit.
  • At a 0% tax rate, after-tax return equals pretax return.
  • This calculator does not estimate tax deductions, credits, loss carryforwards, loss offsets, or other tax treatment arising from an investment loss.

Worked example

$10,000 at 12% pretax with a 25% user-supplied estimated tax rate → pretax gain $1,200, estimated tax $300, after-tax gain $900 (9.00%), ending value $10,900.

A −20% pretax return with any tax rate still shows $0 estimated tax and a −20% after-tax return.

Important assumptions

  • Tax estimate uses only the user-supplied estimated tax rate.
  • No federal brackets, capital-gains brackets, NIIT, state tax, filing status, or jurisdiction rules are applied.
  • Pretax return is a simple return over the modeled period — not annualized here.
  • Estimated tax applies only to positive modeled gain.

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