Mortgage Repayment Calculator: instructions, examples and limits

What it does

Monthly payment = P × r ÷ (1 − (1 + r)^−n), where P is principal, r is nominal annual rate ÷ 12, and n is term in months. The schedule rounds each monthly interest amount and payment to 0.01; extra repayments reduce principal immediately.

Use this estimator to explore how principal, rate, term and extra payments affect a scheduled repayment—not to obtain a lender quote.

How to use it

1. 1

   Enter the balance, nominal annual rate and term using the units shown.

2. 2

   Optionally add a recurring extra payment and compare the interest and time saved.

3. 3

   Record the assumptions and confirm fees, compounding and lender rules with the actual provider.

How the result is produced

Monthly payment = P × r ÷ (1 − (1 + r)^−n), where P is principal, r is nominal annual rate ÷ 12, and n is term in months. The schedule rounds each monthly interest amount and payment to 0.01; extra repayments reduce principal immediately.

Important limits

Fixed-rate estimate with monthly payments at month-end. Excludes fees, taxes, insurance, escrow, offset accounts, rate changes and lender-specific rules. Results use the same currency units as the input and are not financial advice.

Checks before sharing or relying on the result

• The model uses fixed nominal APR with monthly compounding and cent-rounded scheduled payments.
• It does not include taxes, insurance, fees, rate changes, redraw rules or lender-specific offsets.
• Zero or invalid balances are rejected so an apparent answer is never silently fabricated.

Choosing the next step

Enter values in the units and convention named by the page, then compare the displayed formula with your question. For money, change the assumptions rather than treating an estimate as an offer; for statistics, decide whether the data represents a sample or a full population.