Author
BetterProduct Editorial Team
Percentages are everywhere — from sale prices and tax rates to test scores and investment returns. Yet many people struggle with percentage calculations, especially when they involve increases, decreases, or working backwards from a result. This guide covers all the essential percentage calculations you'll encounter in everyday life, with clear examples.
BetterProduct Editorial Team
Checked against standard math or conversion logic and browser-side calculation behavior.
March 2026
Quick everyday calculations and unit checks.
7 language editions aligned from the same source formulas.
Finding X% of Y: multiply Y by (X/100). Example: 15% of $80 = 80 × 0.15 = $12. Finding what percentage X is of Y: (X/Y) × 100. Example: 45 out of 60 = (45/60) × 100 = 75%. Finding the original value when you know a percentage: divide by the percentage as a decimal. Example: $60 is 75% of what? 60 ÷ 0.75 = $80.
Percentage increase: ((New − Old) / Old) × 100. Example: price rises from $80 to $100 → ((100−80)/80) × 100 = 25% increase. Percentage decrease: ((Old − New) / Old) × 100. Example: price drops from $100 to $75 → ((100−75)/100) × 100 = 25% decrease. Note: a 25% increase followed by a 25% decrease does NOT return to the original — it results in a 6.25% net decrease.
When multiple percentage changes are applied sequentially, they multiply rather than add. A 20% increase followed by a 10% decrease: 1.20 × 0.90 = 1.08, which is an 8% net increase. This is why stacked discounts don't simply add: 20% off + 10% off = 28% total discount, not 30%. Always calculate compound changes by multiplying the decimal factors.
Interest rates, investment returns, and inflation are all expressed as percentages. Annual Percentage Rate (APR) is the yearly cost of borrowing. Annual Percentage Yield (APY) includes compounding effects. A 5% APR compounded monthly has an APY of 5.12%. When comparing financial products, always compare APY for savings and APR for loans.