How it is calculated
- What is X% of Y? (X ÷ 100) × Y
- X is what percent of Y? (X ÷ Y) × 100
- Percentage change from X to Y: ((Y − X) ÷ |X|) × 100 — positive is an increase, negative a decrease.
- Add or subtract a percentage: Y × (1 ± X ÷ 100)
Worked example
A phone costs 2,400 with a 15% discount: the discount is 0.15 × 2,400 = 360, so the new price is 2,040. If a salary rises from 8,000 to 8,600, the increase is (600 ÷ 8,000) × 100 = 7.5%.
Frequently asked questions
What is the difference between percent and percentage points?
If a rate moves from 4% to 5%, that is a rise of one percentage point — but a 25% increase relative to the original value.
Does +20% then −20% bring me back to the start?
No. 100 becomes 120, then 96, because the decrease applies to the larger new value.
How do I find the original price before a discount?
Divide the sale price by (1 − rate/100). For example 85 after a 15% discount was 85 ÷ 0.85 = 100.
How do I turn an exam score into a percentage?
Divide your mark by the maximum and multiply by 100 — use the "X is what percent of Y" option.