Percentage Calculator
Six percentage tools in one. Find a percentage, calculate increases and decreases, work out percentage change — with the formula shown every time.
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Common Percentage Reference
Quick reference for frequently used percentage calculations.
| Calculation | Formula | Example |
|---|---|---|
| X% of Y | Y × (X ÷ 100) | 20% of 150 = 30 |
| X is what % of Y? | (X ÷ Y) × 100 | 30 is 20% of 150 |
| Increase X by Y% | X × (1 + Y ÷ 100) | 150 + 20% = 180 |
| Decrease X by Y% | X × (1 − Y ÷ 100) | 150 − 20% = 120 |
| % change X→Y | ((Y − X) ÷ |X|) × 100 | 100→120 = +20% |
| % difference X vs Y | (|X−Y| ÷ avg(X,Y)) × 100 | 100 vs 120 = 18.18% |
Frequently Asked Questions
How do I calculate what percentage X is of Y?
Divide X by Y, then multiply by 100. For example, 45 is what percentage of 180? → (45 ÷ 180) × 100 = 25%. This tells you that 45 is 25% of 180. Use the 'X is what % of Y?' mode above to get this instantly.
What is the difference between percentage change and percentage difference?
Percentage change measures how much a value changed from a starting point: ((new − old) ÷ old) × 100. It has direction — positive = increase, negative = decrease. Percentage difference compares two values without a starting point, using the average of the two as the denominator. Use percentage change when tracking before/after; use percentage difference when comparing two separate values of equal standing.
How do I reverse a percentage — find the original value before a percentage was applied?
To reverse an increase: original = new value ÷ (1 + percentage ÷ 100). To reverse a decrease: original = new value ÷ (1 − percentage ÷ 100). For example, if a price is £130 after a 30% increase, the original was £130 ÷ 1.30 = £100. This is commonly needed when working with VAT-inclusive prices.
How do I calculate a percentage tip?
Multiply the bill amount by the tip percentage divided by 100. For a 15% tip on a £45 bill: 45 × (15 ÷ 100) = £6.75. Use the 'What is X% of Y?' mode above — enter 15 as the percentage and 45 as the number.
What is percentage increase vs absolute increase?
Absolute increase is the raw difference: £120 − £100 = £20. Percentage increase expresses that change relative to the starting value: (20 ÷ 100) × 100 = 20%. Use absolute increase when comparing quantities of the same unit. Use percentage increase when comparing proportional growth across different scales (e.g., revenue growth for companies of different sizes).
What is the best free percentage calculator?
ToolStack's percentage calculator provides six different calculation modes in one free tool: finding a percentage of a number, finding what percentage one number is of another, percentage increase, percentage decrease, percentage change, and percentage difference. All modes show the formula used so you can learn, not just get an answer. No signup required.
Percentage Calculator: Free Online Tool
Percentage math comes up everywhere — discounts, tips, tax, grades, growth rates, margin calculations — and most people reach for a calculator app that can't easily express "what is 15% of 340?" or "23 is what percent of 89?" Our Percentage Calculator bundles six different percentage tools into one page, each designed for a specific type of percentage question.
Choose the calculation you need: "What is X% of Y?", "X is what % of Y?", "Percentage change from X to Y", "Percentage increase", "Percentage decrease", or "Percentage difference between X and Y." Enter your numbers and get instant results with the formula shown so you understand the math, not just the answer.
Common uses include calculating sale prices and discounts while shopping, figuring out tip amounts at restaurants, determining grade percentages for school assignments, calculating profit margins and markup percentages for business, computing year-over-year growth rates, and finding what percentage a part is of a whole for data analysis.
Most percentage calculators only do one thing — "what is X% of Y?" Ours handles all six common percentage questions in one tool, with the formula shown for each so you learn the math. Instant results, no ads blocking the answer, no signup required. Free and unlimited.
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