Extra Mortgage Payment Calculator

How much interest and time do I save by paying extra each month?

Single calculationv1.0.0Verified 2026-11-01Runs in your browser

Spec sheet

extra_principal_schedule · v1.0.0

Method

Month-by-month schedule with extra principal

01interest = balance × r (rounded to the cent)
02principal = payment + extra − interest
03repeat until the balance is 0

Limits — read before relying on it

Assumes the lender applies extra payments to principal immediately and there is no prepayment penalty.

Sources

Annuity payment formulaformula

Worked example

computed by the same formula

$300k, 6.5 %, +$200/month

Inputs

Loan balance: 300000
Interest rate: 6.5 %
Remaining term: 30 years
Extra payment per month: 200

Result

Interest saved: $103,450.19
Months saved: 83
New payoff (months): 277
Regular payment: $1,896.20

Questions

How is the extra mortgage payment calculated?

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Month-by-month schedule with extra principal. interest = balance × r (rounded to the cent) · principal = payment + extra − interest · repeat until the balance is 0

Example: $300k, 6.5 %, +$200/month?

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Interest saved: $103,450.19; months saved: 83.

What does this calculator not cover?

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Assumes the lender applies extra payments to principal immediately and there is no prepayment penalty.

Where do the numbers come from?

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Sources: Annuity payment formula. The formula is versioned (extra_principal_schedule v1.0.0) and covered by automated tests.

Is my data stored?

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No. The calculation runs in your browser and nothing is sent unless you choose to save a shareable link.

Also searched asextra payment calculator · pay off mortgage early · extra principal payment · how much do i save paying extra on mortgage · early payoff calculator

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