Percentages are everywhere — from tips and taxes to test scores, sale prices and stock returns. But the formulas behind them are simpler than most people remember from school. This guide walks through the three percentage calculations that cover almost every real-world situation, with clean formulas, worked examples and a free percentage calculator you can use right now.
What a percentage actually means
A percentage is just a fraction with 100 on the bottom. When you say 20%, what you really mean is 20 out of 100, or 0.20 as a decimal. That single insight — percent = ÷ 100 — unlocks every percentage calculation you will ever need.
If you can convert between a percentage and a decimal, you can do percentages in your head. 50% becomes 0.5. 8.25% becomes 0.0825. 175% becomes 1.75. Multiply any number by that decimal and you've found that percentage of the number.
How to find X% of a number
This is the most common percentage question in the world: 'what is 20% of 500?'. The formula is straightforward: divide the percentage by 100, then multiply by the number.
Formula: (X ÷ 100) × Y. So 20% of 500 = (20 ÷ 100) × 500 = 100. The same formula handles tips, sales tax, commission, exam weighting and any other 'percent of' question.
- 15% of 80 = 0.15 × 80 = 12
- 7.5% of 240 = 0.075 × 240 = 18
- 125% of 60 = 1.25 × 60 = 75
X is what percent of Y?
This flips the question around. You know the part and the whole, and you want the percentage. The formula divides the part by the whole and multiplies by 100.
Formula: (X ÷ Y) × 100. Example: you scored 425 out of 500 on a test. (425 ÷ 500) × 100 = 85%. Same approach for survey responses, conversion rates and project progress.
Percentage increase and decrease
Percentage change tells you how much something has grown or shrunk relative to its starting value. The formula is the same for both — only the sign changes.
Formula: ((New − Old) ÷ Old) × 100. A positive result is an increase. A negative result is a decrease.
Example: a stock rose from $100 to $150. ((150 − 100) ÷ 100) × 100 = 50% increase. If it dropped from $500 to $300, ((300 − 500) ÷ 500) × 100 = −40%, a 40% decrease.
A common trap: a 50% increase followed by a 50% decrease does NOT return you to the original value. $100 → $150 → $75. Percentages always apply to the current value, not the original.
Real-world percentage examples
- Tip calculation: 18% of a $54 bill = 0.18 × 54 = $9.72
- Discount: 25% off $80 = $80 − (0.25 × 80) = $60
- Salary raise: $52,000 → $56,160 is a 8% raise
- Exam score: 76 out of 90 = 84.4%
- Conversion rate: 450 sales from 12,000 visits = 3.75%
Common percentage mistakes to avoid
- Confusing 'percent of' with 'percent more than'. 200 is 200% of 100, but it's only 100% more than 100.
- Adding two percentages from different bases. A 10% discount plus a 10% discount is not 20% off — it's 19%.
- Forgetting that percentages compound. A 5% annual return for 10 years is much more than 50%.
- Treating percentage points and percent as the same thing. Going from 4% to 6% is 2 percentage points, but a 50% increase.
Use our free percentage calculator
Skip the mental math. SnapFetch's free percentage calculator handles all three cases — percent of a number, what percent X is of Y, and percentage increase or decrease — with instant results, a copy button and a clean mobile layout. No signup, no ads inside the tool, no daily limits.
Try our free percentage calculator — open it in a new tab and bookmark it for daily use.
Ready to try it yourself?
Jump straight into the tool — free, no sign-up.
