Percentage Calculator

What is a percentage?

A percentage is a ratio expressed as a fraction of 100 — the word literally means "per hundred". Saying "15%" is the same as saying 15 out of every 100, or the decimal 0.15. Percentages are everywhere: discounts, taxes, interest rates, exam scores, statistics, tips. They make comparisons fair when totals are different — earning 60 points on a 70-point test (about 86%) is better than 80 on a 100-point test (80%), even though 80 is the bigger raw number.

How to use this calculator

What is X% of Y

Use this when you have a percentage and want to apply it to a number. Common uses: a 15% tip on a $48 dinner, a 25% discount on a $79 item, a 7% sales tax on $1,200. Enter the percentage in X and the value in Y. The result is the part the percentage represents.

X is what % of Y

Use this when you want to know what fraction one number is of another, expressed as a percentage. Useful for grades (24 questions right out of 30), savings rates (saving $400 of a $2,500 paycheck), or progress (15 of 60 tasks done). Enter the part in X and the whole in Y.

% change from X to Y

Use this to measure how much a number grew or shrank in percent. Useful for price changes, performance metrics, weight changes. Enter the original value in X and the new value in Y. A positive result means an increase, negative means a decrease. The formula uses the original value as the reference, not the average — so going from 100 to 150 is a 50% increase, but going from 150 back to 100 is a 33% decrease, not 50%.

The three formulas

What is X% of Y → result = Y × (X ÷ 100). Example: 20% of 150 = 150 × 0.20 = 30.
X is what % of Y → result = (X ÷ Y) × 100. Example: 30 is what % of 150? = (30 ÷ 150) × 100 = 20%.
% change from X to Y → result = ((Y − X) ÷ X) × 100. Example: from 100 to 125 = ((125 − 100) ÷ 100) × 100 = +25%.

Common percentages reference

Quick reference for everyday percentages applied to common round numbers. Use it for tips, discounts, and rough mental math.

Percentage	of 100	of 200	of 500	of 1000
5%	5	10	25	50
10%	10	20	50	100
15%	15	30	75	150
20%	20	40	100	200
25%	25	50	125	250
33%	33	66	165	330
50%	50	100	250	500
75%	75	150	375	750
100%	100	200	500	1000

Frequently asked questions

How do I calculate a tip quickly?

For 10%, move the decimal one spot left ($48 → $4.80). For 20%, double 10% ($9.60). For 15%, add half of 10% to itself ($4.80 + $2.40 = $7.20). This calculator does it instantly with the "What is X% of Y" mode.

Why is going up 50% then down 50% not the same as no change?

Because the second percentage applies to the larger number. 100 + 50% = 150. 150 − 50% = 75, not 100. Each step uses the previous value as its base. This is the asymmetry that makes percentage change tricky in finance and statistics.

What's the difference between percent and percentage points?

If a rate goes from 4% to 6%, that's a 2 percentage point increase but a 50% relative increase (from 4 to 6 is +50%). News headlines often confuse the two — the distinction matters in interest rates, polling, and risk numbers.

Can the result be more than 100%?

Yes. If the part is bigger than the whole ("X is what % of Y" with X > Y), the answer is over 100%. Same for percent change — going from 50 to 200 is a 300% increase. Anything is fair game once you understand the formula.

How do I reverse a discount?

If a sale price is $80 after a 20% discount and you want the original price, divide by (1 − 0.20) = 0.80, giving $100. The same logic applies to taxes: $107 with 7% tax included was originally $107 ÷ 1.07 ≈ $100.

Why does my answer have lots of decimals?

Some divisions don't end cleanly — like 1 ÷ 3 = 33.333…%. The calculator shows up to four decimals; round it as you need (typically 1 or 2 decimals are enough for everyday use).

Percentage Calculator