Percentage Calculator – Percent Of, Change, Increase & Reverse

This percentage calculator answers the five percent questions people ask most: what is X% of a number, what percent one number is of another, how much something went up or down, what a price is after adding or removing a percent, and what the original number was. Pick a tab, type two numbers, and the answer appears with the working shown.

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Percentage Formulas

“Percent” means “out of 100”, so every formula is really about dividing by 100 or multiplying by it at the right moment.

How to Calculate a Percentage of a Number

Divide the percent by 100, then multiply by the number. For an 18% tip on a 47.50 bill: 18 ÷ 100 = 0.18, and 0.18 × 47.50 = 8.55.

You can often do it in your head with 10%. To find 10% of any number, move the decimal point one place left: 10% of 60 is 6. From there, build the percent you need. 5% is half of 10% (3), so 15% of 60 is 6 + 3 = 9. 20% is double 10% (12).

How to Find What Percent One Number Is of Another

Divide the part by the whole, then multiply by 100. If you scored 42 out of 50 on a test: 42 ÷ 50 = 0.84, and 0.84 × 100 = 84%.

The “whole” is always the number after “of”. Swap them and the answer changes: 50 is 119.05% of 42, which is a different question.

How to Calculate Percentage Increase or Decrease

Subtract the old value from the new one, divide by the old value, then multiply by 100. A salary that goes from 50,000 to 54,000 rose by 4,000, and 4,000 ÷ 50,000 × 100 = 8%.

A negative answer is a decrease. Direction matters because the starting value changes:

• 80 to 100 is a 25% increase (20 ÷ 80).
• 100 to 80 is a 20% decrease (20 ÷ 100).

Same gap of 20, different percentages. That’s why the calculator asks for “from” and “to” rather than two loose numbers.

How to Add or Remove a Percentage

To take a percentage off, multiply by what’s left. An 85 jacket at 30% off leaves you paying 70%, so 85 × 0.70 = 59.50. To add a percentage, multiply by 1 plus the percent: a 40 meal with 8% tax is 40 × 1.08 = 43.20.

Doing it in one step avoids a common slip: working out the discount (25.50) and then forgetting to subtract it.

How to Find the Original Number

When you only know the result after a percentage was added or removed, divide by what that result represents.

• After a discount: you paid 48 after 20% off. That 48 is 80% of the original, so 48 ÷ 0.80 = 60. In the calculator, use Find the original with 48 is 80% of what.
• After tax: a receipt shows 86.40 including 8% tax. That’s 108% of the price before tax, so 86.40 ÷ 1.08 = 80.

The trap here is taking 20% of 48 and adding it back. That gives 57.60, not 60, because the 20% was taken from the original price, not from 48.

Percentage Mistakes That Catch People Out

Two discounts don’t add up. 20% off and then another 10% off isn’t 30% off. On 100: 100 × 0.80 = 80, then 80 × 0.90 = 72. That’s 28% off in total, because the second discount comes off a smaller number.

Up then down doesn’t cancel out. A price that rises 20% and then falls 20% ends up lower than it started: 100 → 120 → 96. You’re down 4%.

Percent and percentage points are different. If an interest rate moves from 10% to 12%, it rose by 2 percentage points, but by 20 percent (2 ÷ 10 × 100). News reports mix these up all the time.

Change from zero has no percentage. Going from 0 to 5 is an increase, but there’s no percentage for it, because you can’t divide by zero. The calculator tells you this instead of showing a made-up number.

Over 100% is allowed. 150% of 40 is 60, and growing from 40 to 100 is a 150% increase. Percentages only stop at 100 when you’re describing a share of a whole, like a test score.

Frequently Asked Questions