Find the value that a percentage represents. Common use: calculating discounts, taxes, tips, raises, and commissions.
Find what percentage one number is of another. Common use: test scores, sales targets, survey results, budget spent.
Compare an old value to a new value to find the percentage increase or decrease. Common use: price changes, salary raises, population growth, stock returns.
Compare two values where neither is a baseline. Uses their average as the denominator. Common use: comparing prices from two stores, survey results, lab measurements.
Enter the original price and discount percentage to find the sale price and how much you save. Works for Black Friday, coupons, clearance, and any % off sale.
Calculate tip amount, total bill, and per-person split. Recommended: 15% standard, 18–20% good service, 20–25% excellent service.
Enter cost and selling price (or enter cost + markup %) to get markup percentage, profit margin, and profit amount. Markup is on cost; margin is on sale price.
Calculate your percentage grade and letter grade from points earned vs total possible. Add multiple assignments with weights for a weighted average.
Measure how accurate an experimental or measured value is compared to a known theoretical value. Used in science, engineering, and quality control. Result is always positive.
How to Calculate Percentages — Formulas & Examples
A percentage is a number expressed as a fraction of 100. The symbol % means "per hundred." Here are the eight most common percentage calculations with formulas and worked examples.
1. What is X% of Y? (Percent Of)
Formula: Result = (X ÷ 100) × Y
Example: What is 20% of $250? → (20 ÷ 100) × 250 = $50
Use case: calculating taxes, tips, commissions, discounts applied to a price.
2. X is What % of Y?
Formula: Percentage = (X ÷ Y) × 100
Example: 45 is what % of 180? → (45 ÷ 180) × 100 = 25%
Use case: test scores, sales quota attainment, budget spent.
3. Percent Change (Increase or Decrease)
Formula: % Change = ((New − Old) ÷ Old) × 100
Positive = increase. Negative = decrease.
Example: price rises from $80 to $100 → ((100 − 80) ÷ 80) × 100 = +25%
4. Percent Difference
Formula: % Difference = |A − B| ÷ ((A + B) ÷ 2) × 100
Unlike percent change, neither value is the baseline — the average of both is used.
Example: comparing $90 vs $110 → |90−110| ÷ 100 × 100 = 20%
5. Discount & Sale Price
Formula: Sale Price = Original Price × (1 − Discount% ÷ 100)
Example: 25% off $200 → $200 × 0.75 = $150. You save $50.
6. Markup vs Profit Margin
Markup: ((Sell − Cost) ÷ Cost) × 100 — calculated on cost.
Margin: ((Sell − Cost) ÷ Sell) × 100 — calculated on selling price.
Example: cost $50, sell $75 → Markup = 50%, Margin = 33.3%. Both describe the same $25 profit differently.
7. Percentage Grade
Formula: Grade % = (Points Earned ÷ Total Points) × 100
Example: 38 out of 45 → (38 ÷ 45) × 100 = 84.4% (B)
8. Percent Error
Formula: % Error = (|Experimental − Theoretical| ÷ Theoretical) × 100
Example: expected 100g, measured 96g → |96−100| ÷ 100 × 100 = 4% error