Excel Amortisation Formula

What this does

An amortization schedule shows where every payment goes: early on, most of it is interest and little touches the balance; over time the split flips and principal dominates. Seeing that crossover is what makes the schedule useful — it explains why overpaying early saves so much more interest than overpaying late. Keep the inputs visible and clearly labelled and the whole thing stays auditable — anyone who opens the file later, including you, can see at a glance exactly what feeds the result and change one assumption without hunting through the formula. The difference between a quick fix and a sheet you can trust is the extra minute you spend validating “excel amortisation formula”. Start on a copy or a tiny sample, keep the affected formula visible, and compare the result with the tool above before you touch the real workbook. When a formula is involved, keep the inputs labelled beside it, reference cells instead of typing values, and apply number formatting only after the result checks out. The point is a calculation you can defend to a CFO or an auditor, but the practical win is that someone else can open the file and understand what happened without asking you.

A worked example

On a €250,000 loan at 3.8% over 25 years, the payment is about €1,292. In month one, interest is 250000×3.8%/12 ≈ €792 and only ≈€500 reduces the balance. By the final year almost the entire payment is principal. The yearly table above aggregates all 300 months so you can read the principal/interest split at a glance. Use an amortization schedule to compare the true cost of loan offers, to see the impact of overpayments, or to plan an early payoff. It is the difference between knowing your monthly payment and understanding your loan. A practical tip before you scale it up: build it once on a small block of test data, confirm the number against the tool on this page, and only then point it at your real sheet. That one habit catches almost every mistake while it is still cheap to fix, long before a wrong figure reaches a report or a colleague.

In Google Sheets

If you are in Google Sheets rather than Excel, the good news is that the formula shown here is identical and the workflow barely changes — menus sit across the top instead of in a ribbon, and a few function names differ slightly, but anything you build here moves across with little or no rework. Keep this page bookmarked for the next time the same question comes up. Better still, rebuild the example once in your own sheet — doing it yourself, with the tool above to check against, is what turns a copied formula into a technique you own. Treat “excel amortisation formula” as a small building block rather than a chore. Once the inputs sit in their own cells and the formula reads from them, the same setup answers a dozen related questions with a tweak, and Excel keeps every dependent figure current as the data changes. The tool above is there so you can rehearse and verify before committing anything to a real workbook; the steps and worked example are there so the logic sticks. Get it right once and it stops costing you time — it starts saving it, every time the question comes back around.

Common mistakes

• Letting rounding leave a tiny non-zero balance at the end — adjust the last payment to clear it.
• Applying the annual rate per month instead of rate/12.
• Forgetting that extra principal payments change every subsequent interest row.
• Building 360 rows by hand instead of copying one correct formula row down.

Frequently asked questions