Formula
Monthly payment = P × r(1+r)^n ÷ ((1+r)^n − 1). Each month: interest = opening balance × r; principal paid = payment + extra payment − interest; new balance = opening balance − principal paid.
Mortgage Amortization Calculator
Show a mortgage amortization snapshot with scheduled payment, extra principal, selected payment number, interest paid and remaining balance.
Worked example
For 250,000 at 6.5% over 30 years, r = 0.065 ÷ 12 and n = 360. The scheduled monthly payment is about 1,580.17. Month 1 interest is about 1,354.17, so only about 226.00 reduces principal before any extra payment.
Professional note
Master’s Tip: print the selected payment row beside the lender statement. Small rate changes, fee timing, skipped payments or a different compounding convention can explain why a lender balance is not exactly the same as a simple public calculator.
Regional and unit assumptions
Standard or basis: fixed-rate monthly amortization using ordinary annuity-payment arithmetic. It is currency-neutral and does not claim compliance with any named lender, mortgage disclosure or consumer-credit rule.
Assumptions and limitations
- The loan has a fixed annual rate converted to a monthly rate.
- Payments are monthly and the first payment is one month after the starting balance.
- Extra monthly payment is treated as principal reduction with no fee or prepayment penalty.
- Taxes, insurance, redraw fees, offset accounts, variable-rate changes and lender servicing fees are excluded.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Monthly payment = P × r(1+r)^n ÷ ((1+r)^n − 1). Each month: interest = opening balance × r; principal paid = payment + extra payment − interest; new balance = opening balance − principal paid.
Standard or basis
Standard or basis: fixed-rate monthly amortization using ordinary annuity-payment arithmetic. It is currency-neutral and does not claim compliance with any named lender, mortgage disclosure or consumer-credit rule.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master's Tip
Master’s Tip: print the selected payment row beside the lender statement. Small rate changes, fee timing, skipped payments or a different compounding convention can explain why a lender balance is not exactly the same as a simple public calculator.
Related calculators
Questions
What does an amortization calculator show?
It shows how a fixed loan payment is split between interest and principal over time, and estimates the remaining balance after a chosen payment number.
Why is early principal reduction so small?
Early in an amortizing loan, the balance is high, so more of each payment goes to interest. Principal reduction usually grows later as the balance falls.
Do extra payments always save interest?
They can save interest when the lender applies the extra amount directly to principal and there is no prepayment penalty. Check the actual loan terms before relying on the estimate.
Does this match my lender statement exactly?
Not always. Real statements may include fees, rate changes, payment timing, escrow, offset accounts, rounding and local disclosure rules that are outside this simple formula.
What payment number should I use?
Use 12 for roughly one year of monthly payments, 60 for five years, or the exact instalment number shown on your lender statement.
Calculation note
Amortization turns borrowing into a time schedule. The same monthly payment can hide a changing split: interest dominates at first, then principal reduction accelerates as the outstanding balance falls.
A payment is not all principal
In a fixed-rate amortizing loan, each instalment first covers that month’s interest on the outstanding balance. Whatever remains reduces principal. That is why the printable report keeps payment number, interest to date and remaining balance visible together.
Extra principal payments change the path
When a lender applies extra payments directly to principal, the balance falls sooner and future interest is charged on a smaller amount. The calculator models that simple path, but it does not know lender-specific penalties, redraw rules or payment posting dates.
APR and disclosures are broader than a schedule
An amortization schedule is arithmetic. Borrowing decisions may also depend on APR, comparison rates, fees, taxes, insurance, escrow, local disclosure rules and whether the rate can change. Those items should be checked with the official lender documents.
Sources and further readingConsumer Financial Protection Bureau: Interest rate and APRFederal Reserve: Consumer credit