The Percentage Calculator answers four common percent questions in one place. You can find the percent change between two values, take a percent of a number, measure the symmetric difference between two values, or work out what percent one number is of another. Pick the mode you need and the form only shows the inputs that question requires, so you never re-read a label that doesn't apply.
Results update as you type.
Pick the percent question you want to answer — change between two values, X percent of a number, percent difference between two values, or X is what percent of Y — and the form shows only the inputs that mode needs. The answer comes back in the same units you entered, with a plain-English summary of the result.
Subtract the old value from the new value, divide by the absolute value of the old value, then multiply by 100. A positive answer is an increase; a negative answer is a decrease.
Percent Change = ((New − Old) ÷ |Old|) × 100
Signed percentage change between two values. Positive means an increase; negative means a decrease. Uses the magnitude of the old value so negative starting values still produce intuitive direction.
Divide the percent by 100 to convert it to a decimal, then multiply by the total. 15% of 200 is 0.15 × 200 = 30.
Percent of Total = (Percent ÷ 100) × Total
Take a fixed percent of a base number — the most common percent question (sales tax, tip, discount).
Take the absolute gap between the two values, divide by the average of their absolute values, then multiply by 100. Use this when neither value is clearly the baseline.
Percent Difference = (|A − B| ÷ ((|A| + |B|) ÷ 2)) × 100
Symmetric percent difference. The denominator is the average of the two absolute values, so swapping the inputs returns the same answer. Always non-negative.
Divide the part by the whole, then multiply by 100. 30 divided by 200 is 0.15, so 30 is 15% of 200.
Percent = (Part ÷ Whole) × 100
X is what percent of Y. The reverse of percent-of-a-number; useful when you have the part and the whole and need the rate.
Choose a mode and the form shows only the inputs that mode needs. Percent change subtracts the old value from the new and divides by the absolute value of the old to keep direction stable when values are negative. Percent-of-a-number multiplies the rate by the base. Percent difference uses the average of the two absolute values as the denominator so swapping inputs gives the same answer. The X-is-what-percent-of-Y mode divides the part by the whole and multiplies by 100. Each mode validates against division by zero so you never get an undefined result.
Maya's project management app raised its monthly fee from $80 to $100. She switches to percent-change mode and enters 80 as the old value and 100 as the new value.
First, find the absolute change: 100 − 80 = $20. Then divide that by the old price and multiply by 100: 20 ÷ 80 × 100 = 25%.
Since the new price is higher, this is an increase. Maya now pays 25% more each month than she did before.
A buyer is looking at a $200 jacket marked 15% off and wants to know the dollar discount before tax. He picks percent-of-a-number mode and enters 15 for the percent and 200 for the total.
The calculator divides 15 by 100 to get 0.15, then multiplies by 200: 0.15 × 200 = $30. The discount is $30, so the sale price is $200 − $30 = $170 before any tax.
Two technicians independently measured the same sample and got 80 and 100. Neither is treated as "the" baseline, so percent change would be misleading — percent difference is the right tool.
The absolute gap is |80 − 100| = 20. The average of the absolute values is (80 + 100) ÷ 2 = 90. Divide and multiply by 100: 20 ÷ 90 × 100 ≈ 22.22%.
The two readings differ by about 22%. Swapping the order returns the same answer because the formula is symmetric.
A student gets 30 questions right on a 200-question practice exam and wants the percentage. She picks X-is-what-percent-of-Y mode, enters 30 for the part and 200 for the whole.
The calculator divides 30 by 200 to get 0.15, then multiplies by 100: 0.15 × 100 = 15%.
30 is 15% of 200. This is the inverse of asking "what is 15% of 200," which returns 30.
A shopper checks 25% off a $200 sweater with the percent-of-a-number mode. An investor uses percent change to read a portfolio's quarterly move. A scientist comparing two lab measurements reaches for percent difference because neither value is the obvious baseline. A student answers "30 is what percent of 200" with the X-is-what-percent-of-Y mode.
Percent change is the right answer when one value clearly came first — a starting price, a baseline measurement, last quarter's number. Percent difference is for two readings where neither is the obvious baseline, like two independent lab measurements or two competing estimates. Percent-of-a-number is the workhorse for tax, tip, discount, and commission. X-is-what-percent-of-Y is the reverse of percent-of-a-number and answers "how does 30 relate to a total of 200" without making you compute the rate by hand.
These two are easy to confuse but answer different questions. Percent change uses the old value as the denominator and is signed: rising from 80 to 100 is +25%, falling from 100 to 80 is −20%. Those two answers aren't equal because the denominator is different in each direction. Percent difference uses the average of the two absolute values as the denominator, so the answer is the same regardless of which value you list first — 80 and 100 always differ by about 22.22%, no matter how you label them.
Every mode in this calculator surfaces a clear error rather than a silent NaN when the denominator would be zero. Percent change rejects a zero old value because there's no meaningful answer to "how much did zero change." X-is-what-percent-of-Y rejects a zero whole. Percent difference rejects two zero inputs because the average is zero. The other inputs are free to be zero — for example, taking 0% of 200 is a legitimate question and returns zero.