Percentage Calculator: 7 Everyday Math Problems, Solved Instantly
Percentages are everywhere: the 30% discount sign in the window, the 15% tip on the bill, the 5% sales tax, your exam score of 87%, a 20% rise in the price of fuel. You do not need to be a math genius to handle them — you just need the right formula for each situation. This guide covers the three core percentage calculations and the seven everyday problems they solve.
The Three Percentage Formulas You Actually Need
- X% of Y → (X ÷ 100) × Y. Example: 20% of 150 = 30
- X is what % of Y → (X ÷ Y) × 100. Example: 30 is 20% of 150
- % change → ((new − old) ÷ old) × 100. Example: 150 vs 100 = +50%
Our free percentage calculator includes all three modes in one screen, so you never have to remember a formula again.
Problem 1: Discounts (30% Off $80)
A 30% discount means you pay 70% of the price. So $80 × 0.70 = $56. For any percentage, multiply the original price by (100 − discount%) ÷ 100. Our discount calculator does exactly this.
Problems 2 & 3: Tips and Sales Tax
A 15% tip on a $120 bill is 120 × 0.15 = $18, making the total $138. Sales tax works the same way: a 5% tax on $40 adds $2. If you need to split the final amount, our tip calculator handles the per-person share automatically.
Problems 4 & 5: Grades and Statistics
Scored 34 out of 40? That is (34 ÷ 40) × 100 = 85%. Reading that '12% of adults' exercise daily out of a sample of 5,000? That is 600 people. Both are the same 'X is what % of Y' calculation applied to different worlds.
Problems 6 & 7: Price Increases and Investments
Fuel jumped from $1.00 to $1.25 per liter — that is a 25% increase. Your investment grew from $1,000 to $1,180 — an 18% gain. The percentage-change mode of our calculator handles both, including negative results for decreases.
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Frequently Asked Questions
Multiply the number by 0.20 (or divide by 5). Example: 20% of 250 = 50.
Divide the part by the whole and multiply by 100. Example: 45 out of 180 = (45 ÷ 180) × 100 = 25%.
Use ((new − old) ÷ old) × 100. A negative result means a decrease.
5. Simply move the decimal: 10% of any number is one tenth of it.