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Percentage Calculator
Percentages show up in discounts, raises, grades, and stats. This calculator covers the five everyday modes people actually need—without making you rearrange algebra on paper.
Last reviewed July 30, 2026.
When to use this
- Finding what 18% of a number is (tips, commissions, tax estimates)
- Asking what percent one number is of another (scores, market share)
- Measuring percent change from an old value to a new one
Worked examples
20% of 150 = 30. 25 is 12.5% of 200. A change from 100 to 125 is a 25% increase. 200 increased by 10% = 220; decreased by 10% = 180.
Common mistakes
- Mixing up “X% of Y” with “what percent is X of Y”
- Dividing by zero when the whole or starting value is 0
- Reading percent change as percentage points (they are different ideas)
How it works
Percent of: (p ÷ 100) × n. What percent: (part ÷ whole) × 100. Percent change: ((to − from) ÷ |from|) × 100. Increase/decrease: value × (1 ± p ÷ 100).
How to use
- Choose a mode that matches your question.
- Enter the two numbers in the labeled fields.
- Read the result instantly as you type.
FAQ
What is percent change?
It measures how much a value rose or fell relative to the starting number: ((new − old) / |old|) × 100.
Why is “increase by 10% then decrease by 10%” not the original?
Because the second step uses the new base. 100 → 110 → 99.
Can I calculate percentage points?
Percentage points are a simple subtraction of two percents (8% − 5% = 3 points). Use percent change when you care about relative movement.
Does this round results?
Results use up to four decimal places for precision on intermediate math while staying readable.
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