Percentage Calculator

How to Calculate Percentages

A percentage expresses a number as a fraction of 100. The word literally means "per hundred" — so 25% means 25 out of every 100, or one quarter. This calculator handles the four most common percentage calculations in one place, so you don't have to remember the formulas.

The Four Percentage Formulas

1. What is X% of Y?

Multiply the whole by the percentage as a decimal. For example, to find 15% of 200: 200 × 0.15 = 30. Use this for tips, discounts, and tax calculations.

2. X is what percent of Y?

Divide the part by the whole and multiply by 100. For example, to find what percent 30 is of 200: (30 ÷ 200) × 100 = 15%. Use this to calculate test scores, market share, or completion rates.

3. Percentage increase or decrease

Subtract the original from the new, divide by the original, and multiply by 100. For example, a price change from $100 to $125: ((125 − 100) ÷ 100) × 100 = 25% increase. Use this to measure growth, inflation, or salary changes.

4. Add or subtract a percentage

Multiply by (1 + percentage/100) to add, or (1 − percentage/100) to subtract. For example, adding 15% tax to $80: 80 × 1.15 = $92. Use this for applying sales tax, VAT, or discounts.

Real-World Uses

• Shopping discounts. A $60 shirt is 30% off. What is X% of Y tells you the discount ($18); subtracting it gives the sale price ($42).
• Tips at restaurants. Calculate 15%, 18%, or 20% of the bill instantly.
• Grades and test scores. You got 42 out of 50 questions right — what percent is that?
• Business metrics. Revenue growth, profit margins, conversion rates, and market share are all percentages.
• Finance. Interest rates, down payments, and tax rates are all percentage calculations.

Common Percentage Mistakes to Avoid

• Adding percentages directly.A 10% discount plus another 10% off is not a 20% discount — it's a 19% discount, because the second 10% applies to the already reduced price.
• Confusing percentage points with percent. An interest rate rising from 5% to 7% is a 2 percentage point increase, but a 40% relative increase.
• Forgetting the base."200% of" is not the same as "200% more than." 200% of 50 is 100; 200% more than 50 is 150.

Frequently Asked Questions

How do I calculate a discount?

Use mode 1 to find the discount amount (X% of the original price), then subtract it from the original. Or use mode 4 with a negative percentage to get the final price directly.

How do I calculate a tip?

Enter the bill amount as Y and the tip percentage as X in mode 1. For an 18% tip on a $45 bill: 18% of 45 = $8.10.

How do I calculate my test score percentage?

Use mode 2. Enter your points earned as the part and the total possible points as the whole. For 42 out of 50: 42 is what percent of 50 = 84%.