How Mortgage Interest Is Actually Calculated
Why your first years are almost all interest, where the standard payment formula comes from, and what an extra $100 a m…
Amortization Calculator
Build a full amortization schedule showing interest, principal and remaining balance for every payment, month by month and year by year.
Every figure below is labelled in the currency you pick. Amounts are not converted — enter values in the same currency.
$
%
years
$
Monthly payment
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How to use the Amortization Calculator
- Fill in each field with your own figures — the defaults are only there as an example.
- The result updates as you type, so there is no button to press.
- Check the breakdown under the main result for the supporting numbers.
- Use the copy button to take the result with you, or share the link to reload the same inputs.
Amortization Calculator — frequently asked questions
Why is early interest so high?
Interest is charged on the outstanding balance, which is largest at the start. As principal falls, the interest slice of each fixed payment shrinks and the principal slice grows.
Is this amortization calculator free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
How accurate is the result?
The maths is exact for the formula shown on the page. Accuracy in the real world depends on your inputs and on assumptions the formula cannot see, so treat the output as a well-grounded estimate rather than a quote.
Can I use it on my phone?
Yes. The page is responsive, weighs a few kilobytes and works offline once loaded, so it behaves the same on a phone as on a desktop.
Related reading
Focused versions of this calculator
Each of these does one specific job with its own defaults and explanation.
- 3 Year Amortization Calculator Build a full amortization schedule showing interest, principal and remaining balance for …
- 5 Year Amortization Calculator Build a full amortization schedule showing interest, principal and remaining balance for …
- 10 Year Amortization Calculator Build a full amortization schedule showing interest, principal and remaining balance for …
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About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed August 15, 2026 · Calculation runs client-side · No data collected · Report an error