Percentage Calculator
Four calculators in one: find a percentage of a number, apply an increase or decrease, work out the percent change between two numbers, or reverse-calculate the original value before a percentage was applied. Results update as you type.
The formulas behind each mode
% of a Number: (Percent ÷ 100) × Number.
15% of 200 is (15 ÷ 100) × 200 = 30.
Increase / Decrease: Number × (1 ± Percent ÷ 100).
A $50 item increased 20% becomes 50 × 1.20 = $60.
% Change: ((To − From) ÷ From) × 100.
Going from 80 to 100 is a 25% increase.
Find the Original (reverse): Result ÷ (1 ± Percent ÷ 100).
If $45 is the price after a 10% discount, the original price was 45 ÷ 0.90 = $50.
Frequently asked questions
How do you calculate a percentage of a number?
Divide the percentage by 100 to get a decimal, then multiply by the number. For example, 15% of 200 is (15 ÷ 100) × 200 = 30. The "% of a Number" tab above does this instantly for any two values.
How do I calculate a percentage increase or decrease?
Multiply the original number by 1 plus the percentage (as a decimal) for an increase, or 1 minus the percentage for a decrease. A $50 item increased by 20% becomes 50 × 1.20 = $60; decreased by 20% it becomes 50 × 0.80 = $40.
What is a reverse percentage calculation?
It answers "what was the original number before this percentage was applied?" — useful when you know a discounted price or a grown value but not the starting point. Divide the result by (1 plus or minus the percentage as a decimal): if $45 is the price after a 10% discount, the original price was 45 ÷ 0.90 = $50.
How do I calculate the percentage change between two numbers?
Subtract the original value from the new value, divide by the original value, then multiply by 100. Going from 80 to 100 is ((100 − 80) ÷ 80) × 100 = 25% increase. A negative result means a decrease.
Why do I get a different answer than a percentage increase followed by the same percentage decrease?
Because each percentage applies to a different base. Increasing 100 by 20% gives 120, but decreasing 120 by 20% gives 96, not 100 — the second 20% is taken from a larger number. This is a common source of confusion in discount and markup math.