Mortgage repayment calculator
Repayments use the standard amortisation formula: P x [r(1+r)^n] / [(1+r)^n - 1]. Enter the loan amount, rate and term to calculate.
Principal against interest over 25 years57.0% principal · 43.0% interest
Principal$500,00057.0%Interest$376,88543.0%
Source: Freddie MacUsing Freddie Mac rates
How it works
The calculator uses the standard amortising loan formula. Each repayment covers the interest accrued since the last one, and whatever is left over reduces the balance. Early on, most of the payment is interest. Later, most of it is principal.
Changing frequency recalculates the payment, not the loan term. Interest uses the annual rate divided by payments per year, so total interest varies slightly with frequency.
The formula
Nothing is hidden here. This is the calculation running behind the number above.
payment = P × r ÷ (1 − (1 + r)⁻ⁿ)
Pthe amount borrowed
rthe interest rate for one period — annual rate ÷ payments per year
ntotal number of payments — years × payments per year
A worked example
Borrow $500,000 at 5.00% over 25 years, repaid monthly. The period rate is 5.00% ÷ 12, and there are 300 payments.
Common questions
Is this the whole cost of the loan?
It covers principal and interest. Application fees, insurance and anything your lender bundles into the payment sit outside this calculation.
What happens when my fixed period ends?
You move to whatever rate applies then. This calculator assumes one rate for the whole term, so treat long-term totals as a shape rather than a promise.
Do extra repayments help?
Every extra amount comes straight off the balance, so it removes every future interest charge on that amount. Check whether your loan caps extra repayments first.
Why does my lender quote a different number?
Rounding, fee treatment and daily versus per-period interest all differ between lenders. Expect a small gap, not a large one.
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Written up, with the page each rule came from.
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