Percentage Calculator
Three tools in one: find a percentage of a number, figure out what percent one number is of another, or calculate percent change between two values.
What is X% of Y?
X is what percent of Y?
Percent change from X to Y
The three percentage formulas
Most percentage questions are one of three problems:
Example 1: What is 15% of $200? Answer: 200 × 0.15 = $30. Example 2: $30 is what percent of $200? Answer: (30 ÷ 200) × 100 = 15%. Example 3: A price goes from $150 to $180 — what’s the percent increase? Answer: (180 − 150) ÷ 150 × 100 = 20%.
Why percent change is asymmetric
A 20% increase followed by a 20% decrease does not get you back to where you started. If you go up 20% from 100 you reach 120. Down 20% from 120 brings you to 96, not 100. This asymmetry matters for investment returns, pricing, and any scenario where you apply sequential percentage changes. The way to reverse a percentage increase is to divide by (1 + the rate), not subtract the same percentage.
Percentage points vs. percentages
When an interest rate rises from 4% to 5%, that’s an increase of 1 percentage point. It’s also a 25% increase in the rate itself (because 1 is 25% of 4). Confusing these two is one of the most common errors in financial reporting. Percentage points describe absolute differences between two percentages; percentage change describes relative change.
Compound discounts don’t add up
A 20% discount followed by an additional 10% off does not equal 30% off. The second discount applies to the already-reduced price. The combined discount is: 1 − (0.80 × 0.90) = 1 − 0.72 = 28% off total, not 30%. Retailers know this — now you do too.
What is 20% of 350?
350 × 0.20 = 70. Use the first calculator above for any “what is X% of Y” problem.
How do I calculate a tip?
Multiply the bill by the tip percentage as a decimal. A 20% tip on a $45 bill: 45 × 0.20 = $9. Or use the tip calculator to split it automatically.
What’s the difference between percent and percentage points?
Percent describes a ratio; percentage points describe the absolute difference between two percentages. If your score goes from 60% to 75%, that’s 15 percentage points, but a 25% increase in your score.
How do I find the original price after a discount?
Divide the sale price by (1 − discount rate). A $80 item after a 20% discount means the original was 80 ÷ 0.80 = $100.
Related: Tip Calculator · Compound Interest · Mortgage Calculator