Mortgage & financing

Mortgage Prepayment Calculator

Compare your current mortgage with optional extra monthly and annual lump-sum payments.

What this calculator estimates

See how extra payments affect your mortgage. It combines the inputs below to produce Estimated time to payoff. Every assumption remains editable so the estimate can reflect the property, financing and location being evaluated.

Worked example

Using the displayed sample assumptions, the calculator produces 17 yr 9 mo. This is an illustration, not a market quote. Change one input at a time to understand what drives the result.

Inputs and assumptions

• Current mortgage balance — sample input: 400000 currency units
• Annual interest rate — sample input: 4.5 %
• Remaining amortization — sample input: 20 years
• Extra payment each month — optional — sample input: 200 currency units
• Annual lump sum — optional — sample input: 0 currency units

How to interpret the result

Compare the payment with your total housing budget, not income alone. Compare a conservative case with an expected case and keep a record of the assumptions used.

Common mistake to avoid

Avoid assuming the lowest advertised rate applies to every borrower. Local definitions, taxes, lending practices and measurement requirements can materially change the result.

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Reviewed 2026-09-08.