Most "Excel percentage" problems are not arithmetic problems — they are wording problems. A question that asks for the percentage of a number needs a different formula from one that asks for the percentage change between two numbers. Pick the wrong one and the answer looks plausible but is wrong.
This guide covers the six cases that appear in assignments, budgets and sales reports. Each one gives the formula, a worked example and the formatting step people forget.
1. What is X% of a number?
Multiply the number by the percentage. In Excel a percentage is stored as a decimal, so 15% is 0.15.
=240*15% returns 36. With cells, =A2*B2% where A2 holds 240 and B2 holds 15.
If B2 already contains a formatted 15% (0.15), use =A2*B2 instead. Multiplying by B2% when B2 is already 0.15 divides by 100 twice.
2. What percentage is one number of another?
Divide the part by the whole, then format the cell as a percentage.
=45/180 returns 0.25, displayed as 25% after pressing Ctrl+Shift+%.
If the result shows 0.25 instead of 25%, the cell is formatted as General or Number. The formula is correct — only the display is wrong. Do not multiply by 100 as well, or you will double the scale.
3. Percentage change between two values
Subtract the old value from the new one, then divide by the old value.
=(B2-A2)/A2 — from 200 to 250 returns 0.25, or +25%.
The order matters: A2 is the original and B2 is the new value. Reversing them gives −20%, which is the change needed to get back, not the change that happened.
For a drop, the result is negative. Use =ABS((B2-A2)/A2) only if the direction is already stated elsewhere; otherwise keep the sign.
4. Increase or decrease a number by a percentage
Turn the percentage into a multiplier. To add 15%, multiply by 1.15; to subtract 15%, multiply by 0.85.
=A2*(1+B2%) increases, =A2*(1-B2%) decreases.
This is the formula behind VAT, discounts, price rises and budget uplifts. It is not the same as =A2+A2*B2%, although the result is identical — the multiplier version is shorter and easier to audit.
5. Each row's share of a column total
Divide each row by an absolute total, then copy down.
=A2/SUM($A$2:$A$10) — the dollar signs lock the total range.
Without the $, the denominator shifts on every row and the percentages drift. If the rows add up to 101% or 99%, that is normally rounding, not an error. Use ROUND on the displayed values only if the brief requires exact totals.
6. Percentage points versus percent change
A move from 5% to 6% is +1 percentage point but a +20% change, because (6−5)/5 = 0.20.
Use percentage points when comparing two percentages directly — market share, interest rates, pass rates. Use percent change when describing how much the value itself moved. Mixing the two is one of the most common ways an otherwise correct report loses marks.
A quick reference table
| Question | Formula | Result |
|---|---|---|
| 15% of 240 | =240*15% | 36 |
| 45 of 180 | =45/180 | 25% |
| 200 → 250 | =(250-200)/200 | 25% |
| 240 + 15% | =240*(1+15%) | 276 |
| 240 − 15% | =240*(1-15%) | 204 |
| Share of total | =A2/SUM($A$2:$A$10) | varies |
Why your percentage formula returns the wrong answer
- The percentage is stored as text. A cell showing 15% may actually contain the text "15%". ISNUMBER returns FALSE. Fix with VALUE or re-enter it.
- You multiplied by 100 twice. Either the cell is already formatted as a percentage or the formula includes *100, not both.
- The denominator is relative. Missing $ in a share-of-total formula makes every row divide by a different total.
- You divided by zero. A new value of zero, or an empty original cell, returns #DIV/0!. Guard it with IFERROR or IF(A2=0,"",…).
- You used percent change for percentage points. The formula is right; the interpretation is wrong.
Want the answer without rebuilding the sheet? The free Excel percentage calculator handles all six cases and shows the formula. For function syntax, the Excel function reference lists ROUND, SUM, IFERROR and 140+ others.
If the percentage question is part of a graded workbook and the deadline is close, send the file to an Excel expert — fixed quote, formulas explained, usually within 24 hours.
