How to calculate compound interest
✓ Verified in LibreOffice 25.8.7.3Work out what a starting amount grows to at a given rate, compounded monthly (or any frequency).
The formula
| App | Formula | Notes |
|---|---|---|
| Excel | =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. Every formula here is confirmed by actually executing it.