Percentage Calculator
Free percentage calculator for % of a number, percentage increase, decrease, original price before discount, and what percentage one value is of another.
Calculate any percentage in seconds
Formulas, mental shortcuts, a live calculator, and real-world scenarios — everything you need to work with percentages fast.
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Type and the answer updates instantly. The formula below the result shows exactly how it was calculated so you can learn the method, not just the answer.
Percentage calculator
Choose a calculation type, enter your numbers, get your answer.
Enter values above to see the result
Restaurant tip — how much to leave?
- Your bill is $85. You want to leave a 15% tip.
- Find 10% first: move the decimal left → $8.50
- Find 5%: half of $8.50 → $4.25
- Add them together: $8.50 + $4.25 = $12.75 tip
- Total to pay: $85 + $12.75 = $97.75
What is a percentage?
A percentage is simply a way of expressing a number as a fraction of 100. The word "percent" literally means per hundred. So 45% means 45 out of every 100.
Think of it like a pizza. If a pizza is cut into 100 equal slices and you eat 45 of them, you've eaten 45% of the pizza. You don't always have 100 slices — percentages are a way of converting any fraction into that "out of 100" language so everything is easy to compare.
Find the percentage
% = (Part ÷ Whole) × 100You scored 18 out of 25. Divide 18 by 25, then multiply by 100. Answer: 72%
Find the part
Part = (% × Whole) ÷ 100What is 30% of 150? Multiply 30 × 150, then divide by 100. Answer: 45
Find the whole
Whole = (Part × 100) ÷ %45 is 30% of what? Multiply 45 × 100, then divide by 30. Answer: 150
Percentage increase, decrease & original price
Beyond finding a basic percentage, these are the three calculations you'll use most in real life — for prices, salaries, discounts, and scores.
📈 Percentage increase
Use this when something goes up in value — a price rises, a salary increases, or your score improves. You want to know by how much, expressed as a percentage of the original.
📉 Percentage decrease
Use this when something goes down — a price drops, a stock falls, or your energy bill shrinks. Same logic as increase, but you subtract the other way around.
🏷️ Find the original price (before a discount)
The reverse question: you see a sale price and want to know what the item cost before the discount was applied. This is the most commonly missed formula.
The mental math trick nobody taught you
This single rule makes most percentage calculations doable in your head — faster than reaching for your phone.
The rule: x% of y is always equal to y% of x. You can always swap the two numbers and the answer stays exactly the same. All you need to do is pick whichever version is easier to calculate.
Why does this work?
Because percentage is just multiplication in disguise. 16% of 50 means (16 ÷ 100) × 50. If you flip it, 50% of 16 means (50 ÷ 100) × 16. Multiplication doesn't care which number comes first — the result is always the same.
The skill is spotting which direction gives you a "friendly" number like 10%, 25%, 50%, or a round number. Then it becomes mental math you can do in two seconds.
More examples:
4% of 75 → flip → 75% of 4 = 3 ✓
8% of 25 → flip → 25% of 8 = 2 ✓
12% of 50 → flip → 50% of 12 = 6 ✓
Quick ways to find any percentage
Build every percentage from 10%. Once you know 10% of a number, you can assemble almost any percentage using simple addition, halving, or doubling.
The building block approach: 10% of any number is found by moving the decimal one place to the left. From there, 5% = half of 10%, 20% = double 10%, 15% = 10% + 5%, and so on.
Formula cheat sheet
Every percentage formula you'll ever need, in one table. Bookmark this page and refer back any time.
| Goal | Formula | Example | Answer |
|---|---|---|---|
| % of a number | (P ÷ 100) × Whole | 15% of 200 | 30 |
| What % is X of Y? | (X ÷ Y) × 100 | 45 of 60 | 75% |
| % increase | ((New − Old) ÷ Old) × 100 | 200 → 250 | 25% |
| % decrease | ((Old − New) ÷ Old) × 100 | 500 → 400 | 20% |
| Original before discount | Price ÷ (1 − D%÷100) | $80 after 20% off | $100 |
| Add % on top (tax) | Number × (1 + P%÷100) | $50 + 8% tax | $54 |
| Remove % (discount) | Number × (1 − P%÷100) | $120 − 30% | $84 |
| Flip trick (mental math) | x% of y = y% of x | 16% of 50 | = 50% of 16 = 8 |