Percentage Calculator
Use this tool to calculate percentages in different ways: find a percentage of an amount, reverse-calculate percentages, and measure percentage change.
What does “calculate amount in percentage” mean?
When people ask how to calculate amount in percentage, they usually mean one of five common tasks:
- Find a percentage of an amount (for example, 20% of 500).
- Find what percent one number is of another (for example, 50 is what percent of 200).
- Calculate percentage increase (for example, price rises from 80 to 100).
- Calculate percentage decrease (for example, a discount from 120 to 90).
- Apply a percent increase or decrease to get a new amount.
Percent means “out of 100.” So 25% literally means 25 out of every 100. This idea is the key to every percentage formula.
Core percentage formulas you should know
| Use case | Formula | Example |
|---|---|---|
| Find X% of Y | (X ÷ 100) × Y | 15% of 240 = (15/100) × 240 = 36 |
| X is what % of Y | (X ÷ Y) × 100 | 36 is what % of 240 = 15% |
| % change from A to B | ((B − A) ÷ A) × 100 | From 80 to 100 = 25% increase |
| Increase A by P% | A × (1 + P/100) | 200 increased by 10% = 220 |
| Decrease A by P% | A × (1 − P/100) | 200 decreased by 10% = 180 |
Step-by-step: how to calculate percentage amount
1) How to find a percentage of an amount
If you need to find, say, 18% of 350:
- Convert 18% to decimal: 18 ÷ 100 = 0.18
- Multiply by the amount: 0.18 × 350 = 63
2) How to find what percentage one number is of another
Example: 45 is what percent of 60?
- Divide part by total: 45 ÷ 60 = 0.75
- Multiply by 100: 0.75 × 100 = 75%
3) How to calculate percentage increase or decrease
Example: a salary goes from 2,000 to 2,300.
- Find difference: 2,300 − 2,000 = 300
- Divide by original amount: 300 ÷ 2,000 = 0.15
- Convert to percent: 0.15 × 100 = 15%
Real-life percentage examples
Discount shopping
If a jacket costs $120 and is 25% off, the discount amount is:
25% of 120 = 30
Final price = 120 − 30 = $90.
Tax calculation
If sales tax is 8% and your subtotal is $75:
Tax = 8% of 75 = 6, so total = 75 + 6 = $81.
Exam scores
You got 42 out of 50 questions right:
(42 ÷ 50) × 100 = 84%.
Common mistakes to avoid
- Using the wrong base number: for percentage change, always divide by the original amount.
- Forgetting to divide by 100: 15% is 0.15, not 15.
- Confusing increase with decrease: check whether the final amount is higher or lower.
- Rounding too early: keep extra decimals during calculation, then round at the end.
Mental math shortcuts for percentages
- 10% = move decimal one place left (10% of 250 = 25).
- 1% = divide by 100 (1% of 250 = 2.5).
- 5% = half of 10% (5% of 250 = 12.5).
- 15% = 10% + 5%.
- 20% = double 10%.
These shortcuts are useful for tips, discounts, and quick budgeting.
FAQ: quick answers
How do I calculate 30% of an amount?
Multiply the amount by 0.30 (or multiply by 30, then divide by 100).
How do I find the original amount before a discount?
If final price is 80 after a 20% discount, then final = 80% of original. So original = 80 ÷ 0.8 = 100.
Can percentage be more than 100%?
Yes. If one number is bigger than the reference amount, the percentage can exceed 100%.
Final takeaway
To calculate amount in percentage, first identify what you need: a portion, a comparison, or a change. Then choose the right formula and keep the base value correct. Use the calculator above for fast results, and with a little practice, percentage calculations become easy in daily life, business, school, and finance.