How to use it
- What is X% of Y?, enter the percentage and the total. Example: 15% of 200 = 30. Handy for tips, discounts and tax.
- X is what percent of Y?, enter a part and a whole to see the part as a percentage. Example: 30 out of 120 = 25%. Great for test scores and shares of a total.
- Percentage change from X to Y, enter an old value and a new value to see the percentage increase or decrease. Example: 80 → 100 = +25%.
Every box recalculates the instant you change a number, so you can experiment freely without pressing a button.
The percentage formulas
Behind the scenes the calculator uses three classic formulas. Percent of a number: (X ÷ 100) × Y.One number as a percent of another: (X ÷ Y) × 100. Percentage change:((new − old) ÷ |old|) × 100. Using the absolute value of the original number keeps the sign of the change correct even when you start from a negative value.
Common real-world uses
- Tips & tax: quickly add 10%, 15% or 20% to a bill.
- Sales & discounts: find how much you save, or the price after a percent-off deal.
- Grades & scores: turn “38 out of 50” into a percentage.
- Growth tracking: measure how much a price, audience or metric grew or shrank.
A quick note on percentage change: a rise from 50 to 100 is a 100% increase, but the reverse, 100 back down to 50, is only a50% decrease. The percentages aren’t symmetrical because each is measured against its own starting value, which is exactly why a dedicated calculator helps avoid mistakes.
Frequently asked questions
Why does “what percent of” show a dash when the total is 0?
Dividing by zero is undefined, so there’s no meaningful percentage when the total (Y) is 0. Enter a non-zero total to get a result.
Can it handle decimals and negative numbers?
Yes, all three calculators accept decimals and negative values, and results are rounded to a few decimal places for readability.
What’s the difference between percentage points and percent?
Going from 10% to 15% is a 5 percentage-point rise, but a 50% increase in relative terms. This tool reports relative percentage change.
Results are rounded for display; for accounting or exams, double-check critical figures.