Percentage Calculator
Work out what X% of a number is, what percent one number is of another, or the percentage increase or decrease between two values — all in your browser.
What is X% of Y?
Enter both values to see the result.
Everything is calculated instantly in your browser — your numbers never leave your device.
Frequently Asked Questions
How do I find what percent one number is of another?
Use the second mode ("X is what percent of Y"). Enter the part as X and the total as Y, and it returns (X ÷ Y) × 100 as a percentage.
How do I calculate a percentage increase?
Use the third mode ("Percentage change"). Enter the starting value as X and the new value as Y; if Y is larger, the result is labeled an increase.
Can it do a percentage decrease too?
Yes. The percentage-change mode automatically labels the result an increase or decrease based on whether the value went up or down, and shows the absolute difference.
Understanding the Percentage Calculator
The Percentage Calculator is a free, browser-based tool that solves the three percentage questions people hit most often. Switch between modes with a single tap: find what X% of a number is, work out what percent one number is of another, or measure the percentage increase or decrease between two values. Each mode shows a live result and a plain-English sentence (like "20% of 150 is 30") plus a one-click Copy button. Everything runs entirely client-side in your browser, so your numbers never leave your device and there is nothing to install. It is ideal for tips, discounts, grades, growth rates, and quick everyday math.
How it works
Pick one of the three modes at the top, then fill in the two boxes. In "What is X% of Y?" the tool multiplies your percentage by the value. In "X is what percent of Y?" it divides the part by the total and converts to a percentage. In "Percentage change" it compares a starting value to a new value and labels the result an increase or decrease, along with the raw difference. Results update instantly as you type — there is no Calculate button to press. If a box is empty, contains text, or would divide by zero, you get a friendly message instead of an error, and the Copy button grabs the full result sentence for pasting elsewhere.
Worked example
Say a jacket normally costs 150 and is marked down to 180 after a price hike (or use 180→150 for a drop). In "Percentage change", enter From = 150 and To = 180: the tool returns a +20% increase with a difference of 30. To check a discount instead, use "What is X% of Y?" with X = 25 and Y = 80 to get 20 — meaning a 25% discount saves you 20 off an 80 item, leaving 60 to pay.
Tips & common mistakes
- Mode 2 ("X is what percent of Y") is perfect for test scores: enter your marks as X and the total as Y to see your percentage.
- For a percentage increase or decrease, always put the original value in the "From" box — the tool measures change relative to the starting number.
- A negative result in percentage-change mode (shown with a minus sign) means the value went down; the tool labels it a decrease automatically.
- To find a sale price, calculate the discount with mode 1, then subtract it from the original — e.g. 30% of 50 is 15, so the sale price is 35.
- Results show up to six decimal places and trim trailing zeros, so clean numbers like 30 stay tidy while precise ones keep their detail.
- If you see a zero-division warning, the total (mode 2) or starting value (mode 3) is zero — percentages of or from zero are mathematically undefined.