Percentage Calculator
Three quick percentage answers: a portion, a ratio, and a percent change.
Percentages come up constantly — a tip, a test score, a price change — but the three common questions are easy to mix up. This calculator handles all of them in one place: what a percentage of a number is, what one number is as a percentage of another, and how much a value has risen or fallen in percentage terms. Fill in whichever set of boxes matches your question and the answer appears instantly, worked out entirely in your browser.
The three calculations
Each mode uses a distinct formula:
Portion: (P ÷ 100) × V • Ratio: (V1 ÷ V2) × 100 • Change: ((New − Old) ÷ Old) × 100
So 20% of 150 is 30; 45 out of 60 is 75%; and going from 80 to 100 is a +25% change. The change calculation shows a plus or minus sign so you can tell an increase from a decrease at a glance, and every result is rounded to two decimal places.
Getting the right mode
The trick is matching your question to the right row. "What is X% of a total?" is the portion calculation. "What share is this of that?" is the ratio. "How much did this grow or shrink?" is the change, and here the order matters — the first box is the original value and the second is the new one, because percentage change is always measured against the starting point. Swapping them flips the sign and changes the size of the result.
Frequently Asked Questions
Why does percentage change use the original value as the base?
Because a change is measured relative to where you started. Growing from 80 to 100 is a 25% increase, but shrinking from 100 to 80 is a 20% decrease — the same 20-unit gap gives different percentages because the starting points differ.
Can it show a negative percentage?
Yes. In the change mode, a drop is shown with a minus sign and a rise with a plus sign, so the direction is always clear.
How precise are the answers?
Results are rounded to two decimal places, which is enough for everyday use like discounts, tips, grades, and simple growth figures.
Is anything I type stored?
No. The calculations run in your browser and nothing is uploaded or saved.