How to calculate simple interest
✓ Verified in LibreOffice 25.8.7.3 ✓ Verified in Google Sheets (2026-08-30)Interest that doesn't compound — flat-rate loans, short-term notes, bonds' accrued interest.
The formula
| App | Formula | Notes |
|---|---|---|
| Excel (desktop) | =A2*B2*C2 | A2=principal, B2=annual rate, C2=years. Total repayment: =A2*(1+B2*C2). |
| Google Sheets | =A2*B2*C2 | Identical. |
| LibreOffice Calc | =A2*B2*C2 | Identical. |
How it works
Simple interest is principal × rate × time: $5,000 at 4% for 3 years earns $600, because the interest never joins the principal. Compare with compounding (see the compound-interest recipe): the same money compounded monthly grows by $637 — the gap widens with time and rate. Partial years just go in as fractions: 90 days is C2 = 90/365 (or /360 under some loan conventions — check the contract).
Verified, not just documented
We ran =A2*B2*C2 in LibreOffice 25.8.7.3 (headless, with forced recalculation) and it returned 600 — exactly the expected result. We then ran the same formulas in Google Sheets, executed 2026-08-30: a formula-only workbook goes into Google Drive, which converts it to a Sheet and recalculates every formula with Google’s own engine, and comes back out as .xlsx carrying the values Google computed. It returned 600 for the worked example, the same value LibreOffice produced. Both engines’ numbers on this page are executed results. The Excel formula follows Microsoft’s official documented syntax — we do not run desktop Excel.