How to calculate compound interest
✓ Verified in LibreOffice 25.8.7.3 ✓ Verified in Google Sheets (2026-08-30)Work out what a starting amount grows to at a given rate, compounded monthly (or any frequency).
The formula
| App | Formula | Notes |
|---|---|---|
| Excel (desktop) | =ROUND(A2*(1+B2/12)^(12*C2),2) | A2=principal, B2=annual rate, C2=years, compounding monthly. Or use =FV(B2/12,12*C2,0,-A2). |
| Google Sheets | =ROUND(A2*(1+B2/12)^(12*C2),2) | Identical; FV works too. |
| LibreOffice Calc | =ROUND(A2*(1+B2/12)^(12*C2),2) | Identical. |
How it works
The compound-interest formula is principal × (1 + rate/periods)^(periods × years). $1,000 at 5% compounded monthly for 10 years: 1000 × (1 + 0.05/12)^120 = $1,647.01. Change the 12s to 1 for annual or 4 for quarterly compounding. The built-in FV function gives the same answer — note its principal argument is negative by cash-flow convention.
Verified, not just documented
We ran =ROUND(A2*(1+B2/12)^(12*C2),2) in LibreOffice 25.8.7.3 (headless, with forced recalculation) and it returned 1647.01 — 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 1647.01 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.
Functions used
ROUND — see full Excel, Google Sheets & LibreOffice compatibility for each.
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