Five quick percentage tools: what is X% of Y, what percent one number is of another, percentage change, percentage difference, and adding or subtracting a percent.
X% of Y
12
X ÷ Y × 100
15%
From an old value to a new value
15% · increase
Between two values (order doesn't matter)
40%
Base ± percent
plus 92 · minus 68
A percentage is a fraction of 100. To find X% of Y, multiply Y by X/100. To find what percent one number is of another, divide and multiply by 100.
Percentage change measures growth from an old value to a new one relative to the old value. Percentage difference compares two values relative to their average, so the order doesn't matter.
Percentage change is directional — it compares a new value against an original (old) value. Percentage difference is symmetric — it compares two values against their average, so swapping them gives the same answer.
Yes. Every mode accepts negative and decimal values. A few inputs have no defined answer, so they're blocked: the total (Y) in 'X is what percent of Y' and the starting value in percentage change can't be zero, and percentage difference needs at least one non-zero value.
It is handy for tax, tips, discounts, and markups: enter a base amount and a percent to see the value with the percent added and with it subtracted at the same time.
This calculator handles five common percentage tasks in one place: finding what X% of a number is, figuring out what percentage one number is of another, calculating the percentage change between two values, measuring the percentage difference between two values, and adding or subtracting a percentage from a base number. Type into any card and the answer updates instantly.
The page is split into five independent mode cards, each solving a different percentage question. Each card shows two input fields and displays its result — or a short note if the inputs are incomplete or mathematically impossible — directly below the fields. All five modes work simultaneously, so you can use as many at once as you like.
Enter 15 in the percent field and 80 in the number field of the "What is X% of Y" card. In the "Add / subtract a percent" card, enter 80 as the base and 15 as the percent.
15% of 80 is 12. Adding 15% to 80 gives 92, and subtracting 15% from 80 gives 68 — confirming all three results are consistent.
Percentage change measures a directional shift from an old value to a new one: ((new − old) / |old|) × 100. It has a sign — positive for an increase, negative for a decrease. Percentage difference, by contrast, is order-independent: it divides the absolute gap by the average of the two values, giving a symmetric measure that does not imply direction.
The formula is (X / Y) × 100. Division by zero is undefined, so the calculator shows a note rather than an error or an infinite result. Make sure the denominator is a non-zero value.
Yes. To find a discount amount, use "What is X% of Y" with X as the discount rate and Y as the original price. To find the price after a percentage off or on, use "Add / subtract a percent." The same logic applies to tips, VAT, or any markup.
Each mode uses a direct formula. "What is X% of Y" computes (X / 100) × Y. "X is what % of Y" computes (X / Y) × 100, requiring Y ≠ 0. Percentage change is ((new − old) / |old|) × 100, signed, requiring the old value ≠ 0. Percentage difference is |A − B| / ((|A| + |B|) / 2) × 100, order-independent, requiring the two values not both be zero. "Add / subtract a percent" gives base × (1 + p / 100) and base × (1 − p / 100). All formulas follow standard mathematical definitions as documented on MathIsFun.
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