% Of Number Calculator

What is 15% of 80? You know this. You just don't want to do it in your head at the register.

Use this free percentage calculator to find what X% of a number is. Enter the percent and the number, get the answer. Works for tips, discounts, taxes, grades, commissions, and every "just take 30% off" instruction that has ever caused a pause.

Percent means "per hundred." That is the entire concept. Every percentage problem is that one idea wearing a different hat, and this page covers the hats: percent of a number, what percent one number is of another, and percent change.

What This Percentage Calculator Does

Calculates X% of Y instantly (15% of 80 = 12)
Points you to the sibling tools for "what percent is A of B" and percent increase/decrease
Handles decimals and big numbers without the mental gymnastics
Doubles as a discount, tax, tip, and commission calculator, because those are all the same operation

How to Use the Percentage Calculator

Inputs:

Percent — the percentage (enter 15 for 15%, not 0.15)
Number — the value you are taking the percentage of

Steps:

Type the percent
Type the number
Click Calculate
For "A is what % of B?" use the What Percent calculator; for "from A to B is what % change?" use the Percent Change calculator

How the Calculation Works

Result = (Percent ÷ 100) × Number What percent: (Part ÷ Whole) × 100 Percent change: (New − Old) ÷ Old × 100

Shortcut: X% of Y equals Y% of X. 8% of 50 is hard; 50% of 8 is 4. Same answer
10% trick: move the decimal one place left. 10% of 340 = 34. Then 5% is half (17), 20% is double (68), 15% is 10% + 5% (51)
Increase by X%: multiply by (1 + X/100). Decrease by X%: multiply by (1 − X/100). Two 50% discounts are 75% off, not 100% — retailers count on you forgetting this

Worked Example: 35% of 240

35 ÷ 100 = 0.35
0.35 × 240 = 84
Mental route: 10% of 240 = 24 → 30% = 72 → 5% = 12 → 72 + 12 = 84
A $240 jacket at 35% off costs 240 − 84 = $156. Or you could just not buy the jacket. Bold idea.

Tips (From People Who Have Made These Mistakes)

Reverse it: to find the original price after a discount, divide by (1 − discount). $156 ÷ 0.65 = $240
Percentage points vs percent: going from 10% to 15% is +5 points but a +50% increase. Journalists mix these up daily
Grades: 42 correct out of 50 = 42 ÷ 50 × 100 = 84%. Use the Test Grade calculator for letter grades

Frequently Asked Questions

How do I calculate the percentage of a number?

Divide the percent by 100 and multiply by the number. 20% of 65 = 0.20 × 65 = 13. Or move the decimal: 10% of 65 is 6.5, doubled is 13.

How do I find what percent one number is of another?

Divide the part by the whole and multiply by 100. 30 out of 120 = 30 ÷ 120 × 100 = 25%. The What Percent calculator does exactly this.

How do I calculate percent increase?

(New − Old) ÷ Old × 100. A rent increase from $1,500 to $1,650 is (150 ÷ 1,500) × 100 = 10%. The Percent Change calculator handles increases and decreases.

What is 20% of 50?

10. 0.20 × 50 = 10. Also: 50% of 20 is 10 — the reversal trick works every time.

How do I add a percentage to a number?

Multiply by (1 + percent/100). Adding 8% sales tax to $45: 45 × 1.08 = $48.60. Subtracting works the same with (1 − percent/100).

Mini Roast Disclaimer

We roast the number, not you. Everyone forgets how percentages work the moment money or a waiter is involved. It is practically a reflex.

Reality Check

The math here is exact. The trouble in real life is knowing which number is the base — "50% more" and "50% off" are not opposites, and a 20% drop followed by a 20% rise leaves you 4% down. When a percentage sounds too good or too bad, find the base before reacting.