Percentage Calculator
Calculate percentages and percentage changes
What Is a Percentage Calculator?
A percentage calculator is a tool that works out percentage problems for you — finding a percentage of a number, working out what percent one number is of another, and calculating the percentage increase or decrease between two values. You enter the numbers, and it returns the answer instantly along with the formula it used.
A percentage is simply a number expressed as a fraction of 100 — the word comes from the Latin per centum, "by the hundred." Saying "25%" is the same as saying 25 out of 100, or the fraction 0.25. Because every percentage shares the same base of 100, percentages let you compare very different quantities on a level playing field, which is why they show up in prices, grades, statistics, and interest rates.
This calculator runs entirely in your browser, handles decimals and negative numbers, and shows the working so you can check it — useful whether you're double-checking a discount at the till or a figure in a report.
The Three Core Percentage Formulas (With Examples)
1. What is X% of Y? Multiply Y by X, then divide by 100. To find 25% of 200: 200 × 25 ÷ 100 = 50. To find 15% of 80: 80 × 15 ÷ 100 = 12.
2. X is what percent of Y? Divide X by Y and multiply by 100. So 45 is what percent of 180? 45 ÷ 180 × 100 = 25%. And 30 out of 40 correct answers is 30 ÷ 40 × 100 = 75%.
3. Percentage change (increase or decrease): Subtract the old value from the new one, divide by the old value, then multiply by 100. Going from 50 to 65 is (65 − 50) ÷ 50 × 100 = +30%. Going from 80 to 60 is (60 − 80) ÷ 80 × 100 = −25%. A positive answer is an increase; a negative answer is a decrease.
How to Use This Percentage Calculator
Pick the calculation type
Use the tabs to choose what you're solving: "What is X% of Y?" for a percentage of a number, "X is what % of Y?" to turn a fraction into a percentage, or "% Change" to compare two values.
Enter your numbers
Type your values into the fields. Decimals (like 2.5 or 17.75) and negative numbers are fine — the calculator validates inputs as you go so you don't get a misleading answer from a stray character.
Read the result and the formula
The answer appears instantly, along with the formula used so you can see exactly how it was worked out. That makes it easy to trust the number or spot if you entered a value in the wrong field.
Apply or reset
Use the result in your budget, grade, or report, rounding as needed. Hit Clear to start a fresh calculation without reloading the page.
Everyday Percentage Calculations
Working out a discount
For an item priced at $80 with 25% off, the saving is 80 × 25 ÷ 100 = $20, so you pay $60. To get the sale price in one step, multiply by (100 − discount) ÷ 100 — here, 80 × 0.75 = $60.
Calculating a tip
An 18% tip on a $45 bill is 45 × 18 ÷ 100 = $8.10, for a total of $53.10. For a quick 20%, take 10% (move the decimal one place: $4.50) and double it to $9.
Grades and test scores
Scoring 42 out of 50 is 42 ÷ 50 × 100 = 84%. To compare two tests, use percentage change: improving from 70% to 84% is a (84 − 70) ÷ 70 × 100 ≈ 20% improvement.
Sales tax and price rises
Adding 8% tax to a $120 order is 120 × 1.08 = $129.60. The same trick tracks price increases — a rent going from $1,000 to $1,050 rose (1,050 − 1,000) ÷ 1,000 × 100 = 5%.
Budgeting by percentage
To cap housing at 30% of a $4,000 monthly income: 4,000 × 30 ÷ 100 = $1,200. Splitting income into percentage buckets keeps a budget balanced as earnings change.
Frequently Asked Questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 20% of 150 is 150 × 20 ÷ 100 = 30. A quick shortcut: convert the percentage to a decimal (20% = 0.20) and multiply — 150 × 0.20 = 30.
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. So to find what percent 18 is of 24: 18 ÷ 24 × 100 = 75%. This is the calculation you use for test scores, completion rates, and "how much of the total" questions.
How do I calculate a percentage increase or decrease?
Subtract the original value from the new value, divide by the original value, and multiply by 100. From 200 to 250 is (250 − 200) ÷ 200 × 100 = 25% increase. A negative result means a decrease. Always divide by the original value, not the new one.
How do I quickly work out a discount or a tip?
For a discount, multiply the price by (100 − discount%) ÷ 100 to get the final price directly — a 30% discount on $50 is 50 × 0.70 = $35. For a tip, find 10% by moving the decimal one place left, then scale it: 10% of a $60 bill is $6, so a 15% tip is $6 + $3 = $9.
What's the difference between percentage change and percentage points?
They're not the same. If an interest rate rises from 4% to 6%, that's an increase of 2 percentage points, but a 50% percentage change (2 ÷ 4 × 100). Percentage points compare the raw difference; percentage change compares that difference relative to the starting value.
Can I use decimals and negative numbers?
Yes. The calculator accepts decimals like 2.5% or 17.75 and handles negative values, which is useful for financial figures such as losses or rate cuts. Results are shown to two decimal places, precise enough for everyday and most professional use.
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Last updated: August 21, 2026