Free Online Percent Calculator – Quick and Easy Calculation
Calculate percentages easily. Find what percent of a number is, percent increase/decrease, and more.
Formula
B% of A = A × B ÷ 100 | A is what % of B? = (A ÷ B) × 100 | Percent change = (B −
A) ÷ A × 100 | Percent difference = |A − B| ÷ ((A + B) ÷ 2) × 100 | Percent error
= |Observed − Actual| ÷ |Actual| × 100
Five percentage modes: find a percentage of a number, express one number as a percentage of another, calculate percent change, percent difference, or percent error.
Three types of percentage calculations in one place: finding a percentage of a number (what is 15% of 200?), finding what percentage one number is of another (45 is what % of 180?), and calculating percent change between two values (increase from 80 to 100 = 25% increase).
The three calculations explained
- B% of A: Multiply A by B and divide by 100. So 15% of 200 = 200 × 0.15 = 30. Use this for calculating discounts, tips, tax amounts, or any portion of a total.
- A is what % of B: Divide A by B and multiply by 100. So 45 out of 180 = (45 ÷ 180) × 100 = 25%. Use this when comparing scores, market share, or any ratio.
- A to B change %: Subtract A from B, divide by A, multiply by 100. A price going from 80 to 100 = (100 − 80) ÷ 80 × 100 = 25% increase. Useful for tracking growth, price changes, or any before-and-after comparison.
Everyday situations where this comes up
Sales tax on a purchase. How much to tip at a restaurant (15%? 20%?). The actual discount on an item marked "30% off." Your score on a test (got 37 out of 50? That's 74%). Month-over-month revenue growth. How much of your budget went to rent. Portfolio returns.
Most people encounter percentage calculations multiple times a day without realizing it. Having a quick calculator takes the mental strain out of it — especially for the percent change formula, which most people don't have memorized.
Quick tip: reversing a percentage
If something is 30% off and the sale price is $140, what was the original price? Divide the sale price by (1 − 0.30) = 0.70. So $140 ÷ 0.70 = $200. This is the reverse percentage calculation — you're "undoing" the discount. You can use the B% of A calculator to check: 30% of $200 = $60, and $200 − $60 = $140. ✓
Frequently Asked Questions
What is the difference between "percent of" and "percent off"?
"Percent of" finds a portion of a whole (e.g., 20% of $50 = $10). "Percent off" subtracts that portion from the original (e.g., 20% off $50 = $40).
How do I calculate what percent one number is of another?
Divide the smaller number by the larger, then multiply by 100. For example, 15 is what percent of 60? → 15 ÷ 60 × 100 = 25%.
Percentage Calculations Explained