Loan Amortization Calculator
An amortization schedule is the payment-by-payment story of a loan: what each payment buys in interest, what it buys in principal, and what is left. It is also the clearest way to see what an extra payment does, because the effect is almost never what the size of the payment suggests.
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| Period | Date | Original Interest Paid |
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Why the early payments barely move the balance
Interest is charged on what you still owe, so it is largest at the start — when you owe the most. Early in a long loan the majority of each payment is interest and only a sliver is principal, which is why the balance seems to sit still for years. The proportion flips gradually, and on a 30-year mortgage the crossover point where principal finally exceeds interest arrives surprisingly late.
This is not a quirk to be annoyed at. It follows from a fixed payment against a falling balance, and it is the same arithmetic that makes the end of a loan cheap.
What paying extra actually does
Every extra pound or dollar goes entirely to principal, so it removes not just itself but all the future interest that balance would have accrued. That is why an extra payment made early is worth several made late, and why modest regular overpayments shorten a loan by far more than their size implies.
The schedule takes both shapes: an additional amount every month, and a one-time lump sum applied at the start. Comparing the two is the useful exercise — a windfall now and a small monthly increase often land closer together than expected.
Two things to check against your own loan before acting on any of it. Some lenders apply extra money to the next payment rather than to principal unless you tell them otherwise, which achieves almost nothing; and a few carry prepayment penalties. Both are questions for the lender, not for a calculator.
Whether to overpay at all
Paying down a loan is a guaranteed return equal to its interest rate, which makes it a genuinely good deal against a high-rate debt and a closer call against a cheap one. The comparison worth making is against what the same money would do elsewhere — invested, or put toward a higher-rate balance first. That ordering is what the debt payoff tools work through, and the debt guide covers the snowball and avalanche approaches.