Percentage Calculator
Find a percentage of a number, or the percentage change between two numbers.
What this calculator does
Handles the two most common percentage questions: finding "X% of Y" (like calculating a tip or discount), and finding the percent change between two numbers (like a price increase or a score improvement). Pick the mode, enter your two numbers, and it returns the result instantly.
Who this is for
Anyone calculating a discount or tax, tracking a change in a metric (weight, sales, test scores, stock price), comparing two figures relatively rather than in absolute terms, or double-checking a percentage someone else has quoted before relying on it.
How this calculator works
"X% of Y" multiplies Y by X/100. Percent change is (new value − old value) ÷ old value × 100 — positive means an increase, negative a decrease.
Worked examples
X% of Y: 20% of 150 = 150 × (20/100) = 150 × 0.2 = 30.
Percent change: going from 150 to 180: (180 − 150) ÷ 150 × 100 = 30 ÷ 150 × 100 = 20% increase. Going the other way, from 180 to 150: (150 − 180) ÷ 180 × 100 = −30 ÷ 180 × 100 = −16.7% (a decrease) — notice this isn't the same magnitude as the increase, because the base value is different each time.
Common mistakes
- Confusing percentage points with percent change. Going from 20% to 25% is a 5 percentage-point increase, but a 25% relative increase — these aren't the same thing, and mixing them up is a common source of confusion in statistics and news reporting.
- Using the wrong base for percent change. Percent change is always calculated relative to the original (old) value, not the new one — reversing this gives a different, incorrect answer.
- Forgetting the sign matters. A negative percent change means a decrease — don't drop the sign when reporting or comparing results.
- Assuming a percent increase and decrease of the same number cancel out. A 20% increase followed by a 20% decrease does not return you to the original value, because the second percentage is calculated on a different (larger) base.
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Frequently Asked Questions
What's the difference between percentage points and percent change?
If a rate goes from 20% to 25%, that's a 5 percentage-point increase, but a 25% relative increase (5 is 25% of the original 20). These describe different things and mixing them up is a common source of confusion.
Which number is the "old" value in percent change?
Always the starting value, not the ending one. Percent change = (new − old) ÷ old × 100, so reversing old and new gives an incorrect result.
Can percentage change be more than 100%?
Yes — if a value more than doubles, the percent increase exceeds 100%. For example, going from 10 to 25 is a 150% increase.
Does a 20% increase followed by a 20% decrease return you to the original number?
No. Increasing 100 by 20% gives 120, but decreasing 120 by 20% gives 96, not 100 — because the second percentage is calculated on the new, larger base rather than the original value.