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Mortgage Extra Payment Calculator

Time and interest saved when you pay extra each month.

Estimate how many months you knock off a fixed-rate mortgage and how much interest you save by adding a constant extra payment to every monthly bill.

Nadia Almasri By Nadia Almasri
Published Last reviewed 1 min read

Inputs

$
%
yr
$

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

New payoff months = −log(1 − r·B / (P + extra)) / log(1 + r). Interest saved = original lifetime interest − new lifetime interest.

In depth

Estimate how many months you knock off a fixed-rate mortgage and how much interest you save by adding a constant extra payment to every monthly bill.