What this percentage calculator does
Most percentage questions in daily life boil down to one of three calculations, and each one uses a different formula. This tool puts all three in separate cards so you never have to remember which is which:
- What is X% of Y? — the classic one for tips, sales tax and store discounts.
- X is what percent of Y? — for test scores, progress toward a goal, or how much of your budget something eats up.
- Percentage change from X to Y — for pay raises, price hikes and month-over-month comparisons, with the sign included.
Everything runs in your browser: type two numbers in any card and the answer appears instantly. No spreadsheet formulas, no scratch paper.
How to use it
- Pick the card that matches your question. A quick way to decide: do you have a percentage and an amount (first card), two amounts you want to compare as a share (second card), or a before-and-after pair (third card)?
- Enter both values in that card’s fields — dots and commas both work for decimals.
- Read the answer in the dark result box. For percentage change, a plus sign means an increase and a minus sign means a decrease.
- Edit any number and the result recalculates as you type.
The three formulas
- X% of Y: Y × X ÷ 100
- X as a percent of Y: X ÷ Y × 100
- Change from X to Y: (Y − X) ÷ X × 100
Worked example
Your dinner bill comes to $60 and you want to leave an 18% tip: 60 × 18 ÷ 100 = $10.80, so you pay $70.80 in total. Now the second card: you scored 42 out of 50 on a quiz, which is 42 ÷ 50 × 100 = 84%. And the third: your salary goes from $52,000 to $57,200 a year, so the raise is (57,200 − 52,000) ÷ 52,000 × 100 = 5,200 ÷ 52,000 × 100 = 10%.
Discount cheat sheet
Here is what common discounts do to an $80 price tag:
| Discount | You save | You pay |
|---|---|---|
| 10% | $8.00 | $72.00 |
| 15% | $12.00 | $68.00 |
| 20% | $16.00 | $64.00 |
| 25% | $20.00 | $60.00 |
| 30% | $24.00 | $56.00 |
| 50% | $40.00 | $40.00 |
The pattern is worth memorizing: to find the final price directly, multiply by 100 minus the discount, then divide by 100. A 30% discount means you pay 70% of the sticker price.
Frequently asked questions
How do I estimate a percentage without a calculator?
Anchor on 10%, which you get by moving the decimal point one place to the left, and build from there. Say you want 15% of a $64 bill: 10% is $6.40, half of that is $3.20, and together they make $9.60. For 20%, double the 10% figure; for 5%, halve it.
How do I calculate a discount?
Multiply the price by the discount and divide by 100 to get the savings, or jump straight to the final price by multiplying by what you still pay. A $120 jacket at 30% off: you pay 120 × 70 ÷ 100 = $84, saving $36.
What is the difference between percentage points and percent?
Percentage points measure the absolute gap between two percentages; percent change measures the relative jump. If an interest rate moves from 4% to 5%, it rose 1 percentage point — but the relative increase is 25% (1 ÷ 4 × 100). Headlines mix these up all the time, and the two readings can sound wildly different.
How do I remove a percentage that is already included in a price?
Divide by 1 plus the rate as a decimal — do not subtract the percentage. A receipt of $107.50 that already includes 7.5% sales tax has a pre-tax price of 107.50 ÷ 1.075 = $100. The same logic works for any rate: a bill of 1,180 with an 18% tax baked in comes from 1,180 ÷ 1.18 = 1,000.
Does a 20% increase cancel out a 20% decrease?
No. Start at 100, add 20% and you get 120; take 20% off 120 and you land at 96, not back at 100. The base changes between the two steps, so percentage changes are not symmetric — a handy fact to remember when a store raises prices and then announces a “sale” of the same percentage.