Percentage Calculator

To find X% of Y, multiply Y by (X/100). Example: 15% of 200 = 200 × 0.15 = 30. In everyday use: a 15% tip on a $80 meal = $80 × 0.15 = $12. A 25% discount on a $120 item = $120 × 0.25 = $30 off, so you pay $90.

Divide the part by the whole, then multiply by 100. Formula: (Part ÷ Whole) × 100. Example: 30 is what percent of 200? → (30 ÷ 200) × 100 = 15%. Practical use: scored 42 out of 60 on a test? → (42 ÷ 60) × 100 = 70%.

Percentage change = ((New Value − Old Value) / |Old Value|) × 100. If the result is positive, it's an increase; if negative, it's a decrease. Example: Price went from $80 to $100 → ((100 − 80) / 80) × 100 = +25% increase. Price dropped from $100 to $75 → ((75 − 100) / 100) × 100 = −25% decrease.

These are often confused. A "percentage" is a ratio expressed out of 100. A "percentage point" is the arithmetic difference between two percentages. Example: If interest rates rise from 3% to 5%, that's a 2 percentage point increase, but it's a 66.7% increase in the rate itself (2/3 × 100).

If a number is X% of some unknown whole, divide the number by (X/100). Formula: Whole = Part ÷ (Percent/100). Example: $80 is 25% of what number? → 80 ÷ 0.25 = $320. Practical use: after a 20% discount you paid $64 — what was the original price? → 64 ÷ 0.80 = $80.