How do I calculate percentage increase or decrease?

Subtract the old value from the new, divide by the old value, and multiply by 100. From 150 to 180 is (180 − 150) ÷ 150 × 100 = 20% increase.

Percentage Calculator

Q: How do I calculate a percentage of a number?

Multiply the number by the percentage divided by 100. 20% of 150 is 150 × 0.20 = 30.

Q: How do I find what percent one number is of another?

Divide the part by the whole and multiply by 100. 30 out of 150 is 30 ÷ 150 × 100 = 20%.

The three percentage questions you actually ask — "what is X% of Y," "X is what percent of Y," and "percentage change" — each solved with the steps shown.

What is X% of Y?

Result

—

X is what percent of Y?

Result

—

Percentage increase / decrease

Result

—

The percentage formulas

X% of Y = Y × (X ÷ 100)
A is what % of B = (A ÷ B) × 100
% change = ((New − Old) ÷ Old) × 100

Worked examples

20% of 150 = 150 × 0.20 = 30 · 30 of 150 = 30 ÷ 150 × 100 = 20% · 150 → 180 = 30 ÷ 150 × 100 = 20% increase

Percentages in everyday life

The same three operations cover most real questions: a tip is "X% of Y," a test score is "A is what percent of B," and a price change or raise is percentage change. One common trap: a percentage increase and the reverse decrease aren't symmetric — going up 20% then down 20% doesn't return you to the start (150 → 180 → 144). For money-specific versions see the discount, tip, and sales tax calculators, and for the standalone change tool, percentage change.

Frequently asked questions

How do I calculate a percentage of a number?

Number × (percent ÷ 100). 20% of 150 = 30.

How do I find what percent one number is of another?

Part ÷ whole × 100. 30 of 150 = 20%.

How do I calculate percentage change?

(New − Old) ÷ Old × 100. 150 → 180 = 20% increase.

Related calculators

Last reviewed: July 2026.