Percentage Calculators
Percentage math: increase, decrease, change, and reverse calculations.
Which percentage calculator should I use?
Percentage questions look similar, but the correct formula depends on what you know and what you are trying to find. Use Percentage Calculator for “what is X% of Y?”, What Percentage Is X of Y when you know the part and the whole, and Reverse Percentage when you need to work backward to an original value.
For two values over time, use Percentage Change because the old value is the baseline. For two independent values where neither is the starting point, use Percentage Difference. Increase, decrease, discount, and error calculators provide more specific versions of those common percentage problems.
Percentage formulas at a glance
| Question | Formula | Use |
|---|---|---|
| What is X% of Y? | (X ÷ 100) × Y | Tips, portions, commissions |
| What % is X of Y? | (X ÷ Y) × 100 | Shares, scores, proportions |
| Percentage change | (New − Old) ÷ |Old| × 100 | Before-and-after values |
| Percentage difference | |A − B| ÷ ((A + B) ÷ 2) × 100 | Independent values |
Good to know before you calculate
Most percentage questions fit one of three patterns: finding X% of a number (Percentage Calculator), finding what percentage one number is of another (What Percentage Is X of Y), or finding the original before a percentage was applied (Reverse Percentage).
Percentage change is directional — going from 50 to 65 is +30%, but 65 back to 50 is −23.1%. When neither value is the 'before', use Percentage Difference, which divides by the average instead.
Percentage points and percent are different: a rate moving from 4% to 5% rose one percentage point, which is a 25% increase.