Percentage Calculator
Calculate percent of a number, percent change, and percent increase or decrease.
Written by Golam Rabbani, Founder & Lead Engineer
How to use this percentage calculator
- Select a calculation mode: "X% of Y", "X is what % of Y?", or "% change from X to Y".
- Enter the two numbers in the fields labelled for the chosen mode.
- Press Calculate to see the result with a plain-English explanation.
- Use Copy to put the result on your clipboard, or Reset to clear the inputs.
About this percentage calculator
The percentage calculator solves three everyday percentage problems in one place: finding a percentage of a number, expressing one number as a percentage of another, and calculating the percentage change between two values.
Each mode uses a distinct formula. "X% of Y" computes (X ÷ 100) × Y — for example, 15% of 200 equals 30. "X is what % of Y?" computes (X ÷ Y) × 100 — so 45 is 22.5% of 200. "% change from X to Y" computes ((Y − X) ÷ X) × 100 — a move from 80 to 100 is an increase of 25%. Results are displayed to up to four decimal places so that small differences between values are not lost to rounding.
This percentage calculator is useful for quick maths at work or school — splitting a restaurant bill, working out a discount, comparing test scores, or tracking progress toward a goal.
FAQ
- What does the percentage calculator actually compute?
- It covers three calculations: a percentage of a number (X% of Y), one number as a percentage of another (X is what % of Y?), and the percentage change between two values (% change from X to Y). Select the appropriate tab before entering your numbers.
- What formula does each mode use?
- "X% of Y" uses (X ÷ 100) × Y. "X is what % of Y?" uses (X ÷ Y) × 100. "% change from X to Y" uses ((Y − X) ÷ X) × 100, where a positive result is an increase and a negative result is a decrease.
- How accurate are the results?
- The calculator uses standard JavaScript floating-point arithmetic. "X% of Y" results are rounded to at most six decimal places; percentage and change results are fixed to four decimal places. For everyday use this precision is more than sufficient.
- What happens if I enter zero as the denominator?
- In "X is what % of Y?" mode the Total (Y) field cannot be zero, and in "% change from X to Y" mode the From (X) field cannot be zero. If you enter zero in either position the tool shows an error message instead of a result.
- Does this tool store my numbers?
- No. The percentage calculator runs entirely in your browser. Your inputs are never sent to a server, logged, or saved between visits — closing or refreshing the page clears everything.
- Is the percentage calculator free?
- Yes. It is free to use with no signup, no account, and no usage limit.