Financial Calculators
Percentage, tip, discount, and margin calculators — instant results, no sign-up.
How to Calculate Percentages
Percentages are one of the most commonly used math concepts in everyday life — from shopping discounts to restaurant tips, from tax calculations to investment returns. The word "percent" means "per hundred," so 25% simply means 25 out of every 100.
Three Core Percentage Formulas
| Problem | Formula | Example |
|---|---|---|
| X% of Y | Y × X ÷ 100 | 20% of 150 = 30 |
| X is ?% of Y | X ÷ Y × 100 | 30 is 20% of 150 |
| % Change | (New - Old) ÷ |Old| × 100 | 80 to 100 = +25% |
Tip Calculation Guide
In the United States, 15–20% is the standard tipping range for restaurant service. Here's a quick reference for common bill amounts:
| Bill | 15% | 18% | 20% | 25% |
|---|---|---|---|---|
| $25 | $3.75 | $4.50 | $5.00 | $6.25 |
| $50 | $7.50 | $9.00 | $10.00 | $12.50 |
| $75 | $11.25 | $13.50 | $15.00 | $18.75 |
| $100 | $15.00 | $18.00 | $20.00 | $25.00 |
| $150 | $22.50 | $27.00 | $30.00 | $37.50 |
Understanding Markup vs. Margin
Markup and margin both measure profitability, but they use different denominators. Markup is calculated as a percentage of cost, while margin is a percentage of the selling price. Confusing the two can lead to pricing errors that erode profit.
Markup formula: (Selling Price - Cost) ÷ Cost × 100
Margin formula: (Selling Price - Cost) ÷ Selling Price × 100
For example, if a product costs $40 and sells for $100, the markup is 150% (profit is 1.5× the cost), but the margin is 60% (profit is 60% of the revenue). Higher markups always correspond to higher margins, but the numbers are not interchangeable.
Discount Calculation Tips
To find the sale price, multiply the original price by (1 - discount%/100). For a 30% discount on a $80 item: $80 × 0.70 = $56. Stacking discounts? Apply them sequentially — a 20% off coupon on top of a 10% sale is not 30% off. It's $80 × 0.90 × 0.80 = $57.60.
Quick mental math trick: To calculate 15% of any number, find 10% (move the decimal one place left), then add half of that. For $80: 10% = $8, half = $4, so 15% = $12.