Calculator
Percentage Calculator
Calculate a percentage of a number, find what percent one value is of another, or measure percentage increase and decrease. Your values stay in this browser.
How to calculate percentages
Choose the question that matches the values you already know.
What is X% of Y?
Use X ÷ 100 × Y. For example, 15 ÷ 100 × 80 = 12, so 15% of 80 is 12. This helps you find a portion of a budget, target, or measurement.
X is what percent of Y?
Use X ÷ Y × 100. For example, 12 ÷ 80 × 100 = 15%, so 12 is 15% of 80. Use it to express a part's share of a total or progress toward a whole.
How do you calculate percentage change?
Use (Y − X) ÷ X × 100, where X is the starting value and Y is the ending value. For example, (92 − 80) ÷ 80 × 100 = 15%, which is an increase from 80 to 92. This describes growth or decline between an old and new count, price, or measurement.
Common percentage questions
Which number is the baseline for percentage change?
The starting value X is the divisor and baseline. Reversing direction changes the baseline: 80 → 92 is +15%, while 92 → 80 is −13.043478%. Neither is a percentage difference.
Why do equal percentage increases and decreases not cancel out?
Each change uses a different starting value. 100 increased by 20% becomes 120, then 120 decreased by 20% becomes 96, not 100.
Can you calculate percentage change from zero?
The formula would divide by zero, so the calculator reports an error when X starts at 0. Likewise, the “X is what percent of Y?” calculation cannot use a whole Y of 0.
How the calculator handles results
Inputs and rounding
Enter plain signed numbers and period decimals. Commas, letters, scientific notation, and a trailing decimal point are rejected. Results round to at most six decimal places and trim trailing zeros.
Increase, decrease, and no change
Percent change uses + for an increase, − for a decrease, and 0% for no change. Negative starting values follow the formula literally and may be counterintuitive.
Private, browser-based calculations
Your values are processed in this browser. They are not uploaded or sent to a 247 Tools server, and the calculator does not save a calculation history. Clear removes the current inputs and result from the page.