Offline Mortgage Split Calculator

See how each monthly payment is split into interest and principal, and how extra monthly payments change the result. Works fully offline.

Loan amount

Annual rate %

Term in months

Regular payment

Extra monthly payment

Start extra from month

One time extra amount

One time extra in month

After extra payment, prefer

Include extra accrued interest shown by bank

If yes, extra accrued interest amount

Tip: if your bank says an extra repayment does not replace the next instalment, keep your normal monthly instalment and treat the extra payment as separate principal reduction.

Payoff time

Total interest

Total paid

Next month split

Interest share in month 1

Comparison vs no extra payments

Months saved
Interest saved
Principal paid in month 1
Extra cash this month

Offline file No internet needed CSV export included

This calculator uses standard amortization math. If your bank adds accrued interest on the day of an extra repayment, enable that checkbox to see the effect on total cost.