Calculate Interest on Loan in Excel

What this does

PMT returns the fixed monthly payment that fully repays a loan — principal plus interest — over its term. It assumes a constant rate and equal payments, which is how the overwhelming majority of mortgages, car loans and personal loans are structured. Dividing the annual rate by 12 and multiplying the years by 12 puts everything on a monthly footing; the negative sign on the amount makes the payment show as a positive number. The same idea underpins a lot of everyday Excel work, so the few minutes spent getting it right here pay back across every sheet you build afterwards. Treat it as a pattern, not a one-off, and it stops being something you look up and starts being something you reach for. Treat “calculate interest on loan in excel” as a small repeatable workflow rather than a one-off click you hope to remember next time. Use a small test block before the live file, so any surprise in the affected cells shows up while it is still harmless. 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. That turns a calculation you can defend to a CFO or an auditor into a method you can reuse, explain, and defend when the workbook leaves your screen.

A worked example

A €250,000 mortgage at 3.8% over 25 years: =PMT(3.8%/12, 25*12, -250000) returns about €1,292 a month. Over the full term you repay roughly €387,500, so interest alone is about €137,500 — the area the balance curve above shrinks as you shorten the term or drop the rate. Whether you are comparing mortgage offers, sizing a car loan, or stress-testing a budget against a rate rise, PMT is the one formula that turns a headline rate into the number that actually hits your account each month. One habit worth forming early: name the cells that hold your inputs, so the formula reads in plain language instead of a string of cell addresses. A reviewer — or you in three months — can then follow the logic without decoding what B7 and D2 were supposed to mean, which is most of what makes a sheet maintainable.

In Google Sheets

Google Sheets handles this almost identically to Excel. The formula syntax above is the same, and the menu lives under a slightly different label rather than a ribbon tab. Use the platform toggle at the top of the page to switch every keyboard shortcut between Windows and Mac, and expect at most cosmetic differences in naming. Nothing on this page is behind a login: the tool runs entirely in your browser, the formula is shown in full with one-click copy, and the steps work the same on Windows and Mac. That is the whole promise here — the exact answer, a way to prove it on your own numbers, and just enough context to make it stick. If you take one thing from this page on “calculate interest on loan in excel”, make it the habit rather than the keystrokes: set the problem up with labelled inputs, reference those cells, and let Excel do the recomputing. Bookmark the page for the syntax, but do the example once in a blank sheet and check it against the tool above — five minutes of hands-on practice fixes the method in memory far better than re-reading, and it surfaces the small snags while they are still harmless. After that the technique is genuinely yours: faster than searching for it again, and reliable enough to drop into work that other people depend on.

Common mistakes

• Forgetting to divide the annual rate by 12, which inflates the payment roughly twelve-fold.
• Entering the loan amount as positive, so PMT returns a negative payment.
• Mixing the term and rate periods (annual rate with a monthly term, or vice versa).
• Ignoring fees, insurance or an offset, which the bare PMT figure does not include.

Frequently asked questions