Percentage Calculator: Free Online Percent Calculator
Four common percentage calculations — results update instantly.
What is X% of Y?
e.g. What is 20% of 150? → 30
X is what % of Y?
e.g. 30 is what % of 150? → 20%
Percentage change
e.g. from 80 to 100 → +25%
Increase / decrease by %
e.g. 200 increased by 15% → 230 / decreased → 170
About the Percentage Calculator
Percentages show up everywhere: discounts, tax, tips, test scores, interest rates, budgets. Most people can do the math for one or two of these on the fly, but switching between "what's 15% of this" and "what percent did this change by" mid-conversation is where mental math usually breaks down. This calculator covers the four questions that come up most often, laid out as separate cards so you type your numbers into plain-language sentences and read the answer back instantly, with no formula to remember and no order of operations to get wrong.
The four calculations explained
X% of Y = (X ÷ 100) × Y
X is ?% of Y = (X ÷ Y) × 100
% change = ((New − Old) ÷ |Old|) × 100
Increase by X% = Number × (1 + X ÷ 100)
The first card answers "what is X% of Y," the calculation behind tips, discounts, and commissions. The second flips it around: given a part and a whole, it tells you what percentage the part represents, which is how you'd check a test score or a completion rate. The third card measures percentage change between two values, useful for tracking price moves, weight changes, or year-over-year growth, and it reports the result with a sign so you can tell an increase from a decrease at a glance. The fourth card takes a starting number and shows both outcomes of applying a percentage to it: the value after adding X% and the value after subtracting X%, side by side.
Real-world examples
- 🛍️20% off a $85 item → 20% of 85 = $17 discount → you pay $68
- 📈Stock went from $120 to $156 → % change = +30%
- 🍽️18% tip on a $47 meal → 18% of 47 = $8.46
- 📊Scored 43 out of 50 → 43 is what % of 50 = 86%
Why percentage change trips people up
A common mistake is treating a percentage change as reversible in a straight line: if a price rises 25%, people assume a 25% drop brings it back to where it started, but it doesn't. Going from 80 to 100 is a 25% increase, yet going from 100 back to 80 is only a 20% decrease, because the base you're measuring against changed. The percentage change formula always divides by the starting value, not the ending one, which is exactly why the two directions produce different numbers. The third card handles this automatically. Type the old and new values in either direction and it computes the correct percentage relative to whichever value you entered as the starting point.
Tips for accurate results
Enter negative numbers directly when relevant, such as a percentage change that starts from a negative baseline, and the calculator handles the sign correctly using absolute value in the denominator. When comparing multiple discounts or fee increases, run each one through the calculator separately rather than adding the percentages together. Stacked percentages don't sum the way flat amounts do, since each one applies to a different base value once the first adjustment has already happened.
Common use cases
Shoppers use the first card to check a discount before checkout, since a store's advertised "30% off" means little until you see the actual dollar amount coming off the price. Restaurant diners use it to split a tip without doing the arithmetic in their head at the table. Students and employees use the second card to convert a raw score into a percentage, whether that's a test result or a completion rate on a project. Investors and analysts lean on the third card to track how a price, a metric, or a budget line moved between two points in time, since percentage change communicates the size of a move in a way raw numbers alone don't. Anyone negotiating a raise, a rent increase, or a fee adjustment can use the fourth card to see exactly what a proposed percentage translates to in real terms before agreeing to it.
Local and private
Every calculation runs in your browser using plain JavaScript arithmetic. Nothing you type into any of the four cards is transmitted anywhere, which matters if you're working through salary numbers, medical test results, or other figures you'd rather not send to a server just to do basic math and would prefer to keep off the network entirely. There's no account, no sign-in, and no saved history between visits beyond whatever your own browser remembers.
Related: Unit Converter for measurement conversions, or Break-even Calculator for business margin analysis.
Frequently Asked Questions
Is the Percentage Calculator free?
Yes — completely free. No account and no data sent to a server.
Do I need an account?
No account, no login, and no signup required.
What types of percentage calculations does it support?
Four modes: What is X% of Y (tip and discount), X is what percent of Y (comparing a part to a whole), X is Y% of what (working backward from a percentage), and percentage change from X to Y (before-and-after comparison).
Why is 50% off then 20% off not the same as 70% off?
The second discount applies to the already-reduced price, not the original. At 50% off, $100 becomes $50. Then 20% off $50 is $10, leaving $40 — a 60% total discount, not 70%. Stacked discounts are always less than their sum.