Amortization Calculator
See how a loan payment splits between interest and principal over time.
Your figures
Result
How to use this tool
- Enter your figures in the fields on the left.
- Results update instantly as you type — there is no button to press.
- Change any input to see how sensitive the answer is to it.
Amortisation is front-loaded with interest. On a 30-year mortgage it typically takes about 18 years before you have repaid half the principal, even though you are halfway through the payments.
How it works
The calculation runs in your browser as you type — there is no submit button and nothing is sent anywhere. Change any figure and the results update immediately, which makes it easy to see how sensitive the answer is to each input.
Every formula used here is standard and documented in the questions below. Where a result depends on an assumption, the assumption is stated rather than buried.
Frequently asked questions
Why is so little principal repaid early on?
Interest accrues on the outstanding balance, which is at its highest at the start. As the balance falls, the interest portion shrinks and the principal portion grows.
When do I reach the halfway point?
Later than you would expect. The calculator shows exactly when your balance falls below half the original loan — usually well past the midpoint of the term.
How do extra payments help?
An extra payment goes entirely to principal, removing that amount from every future interest calculation. Early extra payments are worth far more than late ones.
Is this calculator free?
Yes, with no account, no limits and no data collection. It runs entirely in your browser.
Should I rely on this for a financial or medical decision?
No. It is a planning estimate built on standard formulas and stated assumptions. For decisions that matter, speak to a qualified professional who can account for your full circumstances.
Is this calculator accurate?
The arithmetic is exact — it uses the standard formula, shown in the questions above. What limits accuracy is the assumptions: the figures you enter, and factors the formula does not model such as fees, taxes and rule changes. Treat the result as a well-founded estimate rather than a quotation.
Do I need to sign up or download anything?
No. It runs in your browser, updates as you type, and stores nothing. There is no account, no download, and no limit on how many times you use it.
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Your files stay on your device. This tool runs entirely in your browser. No file is uploaded, transmitted, or stored. You can verify this by opening your browser's Network tab while using the tool.
Disclaimer. This calculator provides estimates based on standard formulas and the assumptions stated above. It is not financial, medical, tax or legal advice. For decisions that matter, consult a qualified professional. See our full disclaimer.