Percentage of a number
What is
% of
?
—
% of a number · What percent of · Increase & decrease · All at once · No upload
Percentage Calculator
The three percentage questions people ask most — what is X% of Y, X is what percent of Y, and the percentage increase or decrease between two numbers — all answered at the same time, live as you type. Below them sit three more cards for raising or lowering a value by a percent, working backwards from a known percentage, and the percentage difference between two figures. Set the number of decimals and digit grouping once and every card follows. Everything runs in your browser — no upload, no sign-up.
X is what percent of Y
is what % of
?
—
Percentage increase / decrease
From
to
?
—
Increase / decrease a value by %
±
%
—
Reverse — find the original
is
% of what?
—
Percentage difference
Between
and
?
—
Ready
Key features
Three answers at once
Percent of a number, what-percent-of, and percent change update together as you type, so you never switch modes to compare.
Increase & decrease
Apply a percent up or down to any value, and read the new amount and the size of the change side by side.
Reverse percentage
Work backwards from a known part and percent to recover the original whole — handy for prices before a discount or tax.
Your precision
Pick 0 to 6 decimals, toggle thousands separators and trailing-zero trimming, and every card respects the setting.
Frequently asked questions
How do I calculate X percent of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 200 is 15 ÷ 100 × 200 = 30. The first card does this instantly, and also shows the value with that percent added and removed.
How do I find what percentage one number is of another?
Divide the part by the whole, then multiply by 100. So 30 out of 200 is 30 ÷ 200 × 100 = 15%. Use the “X is what percent of Y” card — it also reports the remaining percentage.
What is the difference between percentage change and percentage difference?
Percentage change has a direction: it measures growth or decline from an old value to a new one, dividing by the old value. Percentage difference is symmetric — it compares two values with no “before”, dividing by their average. Use change for trends over time, difference for comparing two independent figures.
How does the reverse percentage work?
If you know that an amount is a certain percent of an unknown total, divide the amount by the percent expressed as a decimal. For 30 being 15% of a number: 30 ÷ 0.15 = 200. This is how you find a pre-discount or pre-tax price.
Is my data sent anywhere?
No. All arithmetic happens locally in your browser. Nothing is uploaded, and the page keeps working offline once loaded.