Percentage Calculator

Step by step

1. Pick the sentence that matches your question from the row of buttons — they are worded the way people actually ask.
2. Fill in the two boxes. The answer updates as you type; there is no equals button to hunt for.
3. Read The working underneath. Each step shows the substitution, so you can copy the method onto paper.
4. Use Copy answer to lift the result, or tap one of the common examples to load it instantly.

Good to know

• Percent change and percent difference are not the same thing. Change has a starting value and divides by it; difference treats both values as equals and divides by their average. Use change for “before and after”, difference for “these two measurements”.
• A 20% rise followed by a 20% fall does not return you to the start — 100 → 120 → 96. Percentages always act on whatever the current value is.
• To take 15% off in one step, multiply by 0.85. To add 15%, multiply by 1.15. The shortcut appears in the working for the add/subtract mode.
• Marks like 17 out of 20 are the “X is what % of Y” mode — 85%.
• Percentages over 100 are fine and often correct: going from 40 to 100 is a 150% increase.

The maths behind it

• Percent of a number result = P ÷ 100 × N 15% of 80 = 0.15 × 80 = 12.
• X as a percent of Y percent = X ÷ Y × 100 The part goes on top, the whole underneath.
• Percent change change % = (new − old) ÷ |old| × 100 Negative means a fall. The old value is the baseline, which is why the answer changes if you swap them.
• Finding the whole whole = part ÷ (P ÷ 100) Reverses the first formula — useful for backing a pre-tax price out of a total.
• Percent difference diff % = |A − B| ÷ ((|A| + |B|) ÷ 2) × 100 Symmetric: swapping A and B gives the same answer.