Percentage Calculator

Calculate percentage of a number, percent share, and percentage change with formulas and practical examples.

What is X% of Y?

%
30

X is what percent of Y?

/
15%

Percentage change

→
25%

Formula and usage notes

Use this percentage calculator for discounts, grade checks, spreadsheet audits, business reports, and quick everyday math.

Core formulas: X% of Y = Y × X / 100; X as a percent of Y = X / Y × 100; percentage change = (new - old) / old × 100.

Practical examples

Practical examples 1

20% of 150 = 30

Practical examples 2

45 is 15% of 300

Practical examples 3

100 to 125 is a 25% increase

Practical examples 4

A 15% discount on 80 gives 68 before tax

Frequently asked questions

Which percentage formula should I use first?

Use X% of Y when the percent is known, X as a percent of Y when comparing part to whole, and percentage change when there is an old value and a new value.

Why can percentage change be negative?

It is negative when the new value is smaller than the old value. That is usually a decrease.

Should I round percentages early?

Keep extra digits while calculating and round only for display, especially in reports or spreadsheets.