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Kalcufy

Percentage Calculator

What Is a Percentage?

A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin 'per centum,' meaning 'by the hundred.' Percentages are used everywhere in daily life — from calculating discounts and tips to understanding interest rates, test scores, and statistics. When you see 25%, it means 25 out of every 100, or one quarter of the total. The concept makes it easy to compare proportions regardless of the actual quantities involved. For example, saying a product is '30% off' immediately communicates the savings without needing to know the original price.

How to Calculate Percentages

There are three fundamental percentage calculations. First, finding X% of Y: multiply Y by X and divide by 100. For example, 15% of 200 is (200 × 15) / 100 = 30. Second, finding what percent X is of Y: divide X by Y and multiply by 100. For example, 30 is what percent of 200? (30 / 200) × 100 = 15%. Third, percentage change: subtract the old value from the new value, divide by the old value, and multiply by 100. If a price goes from $80 to $100, the change is ((100 - 80) / 80) × 100 = 25% increase. Each formula is simply a rearrangement of the same basic relationship: Part = Percentage × Whole / 100.

Frequently Asked Questions

How do I calculate a percentage of a number?

Multiply the number by the percentage and divide by 100. For example, 20% of 150 = 150 × 20 / 100 = 30.

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

Divide the part by the whole and multiply by 100. For example, 45 is what percent of 200? (45 / 200) × 100 = 22.5%.

How do I calculate percentage change?

Subtract the old value from the new value, divide by the old value, and multiply by 100. Formula: ((New - Old) / Old) × 100.

What is the difference between percentage and percentage points?

If an interest rate goes from 5% to 8%, it increased by 3 percentage points but by 60% as a percentage change ((8-5)/5 × 100 = 60%).

How do I convert a fraction to a percentage?

Divide the numerator by the denominator and multiply by 100. For example, 3/8 = 0.375 × 100 = 37.5%.

How do I reverse a percentage to find the original value?

If you know the final value after a percentage increase/decrease, divide by (1 + rate/100) for increases or (1 - rate/100) for decreases. Example: $120 after a 20% increase means the original was 120 / 1.20 = $100.