How to Calculate a Percentage (3 Common Ways, Explained)

Most real-world percentage questions fall into one of three types — and mixing up which one you need is the most common source of a wrong answer.

1. What is X% of Y?

Formula: (X ÷ 100) × Y

Example: what is 20% of 150? → (20 ÷ 100) × 150 = 30. Useful for tips, discounts and any "take a percentage off/of this number" question.

2. What percent is X of Y?

Formula: (X ÷ Y) × 100

Example: 30 is what percent of 150? → (30 ÷ 150) × 100 = 20%. Useful for scores, completion rates, or "how much of the whole does this represent."

3. What's the percent change between two numbers?

Formula: ((New − Old) ÷ Old) × 100

Example: a price goes from 150 to 180 → ((180 − 150) ÷ 150) × 100 ≈ 20% increase. A negative result means a percent decrease. Useful for price changes, growth rates and comparisons over time.

The mistake that trips people up most

Percent change is always relative to the original (old) value, not the new one — a common error is dividing by the new number instead. A value that goes from 100 to 150 is a 50% increase, but going back from 150 to 100 is a 33% decrease, not 50%, because the "original" value is different each time.

How to calculate a percentage

Enter your numbers into the Percentage Calculator and pick the calculation you need — it handles all three types above instantly.

FAQ

Why isn't a 50% increase followed by a 50% decrease back to the original number? Because each percentage is calculated against a different base value. 100 increased by 50% is 150; 150 decreased by 50% is 75, not 100 — the base changed.

How do I calculate a discount? That's the "X% of Y" case: multiply the original price by the discount percentage to find the amount off, then subtract it from the price (or use our Percentage Calculator directly).

Can percentages go above 100%? Yes — anything more than doubling the original value is over 100% (for example, going from 50 to 120 is a 140% increase).

Calculate a percentage now

Try the free Percentage Calculator for instant, accurate results. See more calculators.