How to reverse a percentage: X is P% of what?
✓ Verified in LibreOffice 25.8.7.3 ✓ Verified in Google Sheets (2026-08-30)You know the part and the rate — recover the whole. Deposits, samples, partial payments.
The formula
| App | Formula | Notes |
|---|---|---|
| Excel (desktop) | =A2/B2 | A2 = the known part, B2 = the rate it represents (15% stored as 0.15). |
| Google Sheets | =A2/B2 | Identical. |
| LibreOffice Calc | =A2/B2 | Identical. |
How it works
If 12 is 15% of something, the something is 12 ÷ 0.15 = 80 — part over rate gives the whole, because part = whole × rate rearranged. The everyday cases: a $500 deposit that's 20% of the job (500/0.2 = $2,500 total), 45 survey responses at a 9% response rate (500 sent). Kin to the before-a-discount recipe — reverse percentage problems always divide, never multiply.
Verified, not just documented
We ran =A2/B2 in LibreOffice 25.8.7.3 (headless, with forced recalculation) and it returned 80 — 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 80 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.