How to Calculate Percentages – Complete Guide
A percentage calculator is one of the most universally useful math tools for students, business professionals, shoppers, and anyone working with data. Our free online percentage calculator handles four key calculation types: finding X% of Y, finding what percent X is of Y, calculating percentage increase or decrease, and calculating percentage difference between two values.
Finding X% of a Number
Formula: Result = (Percentage ÷ 100) × Number. Example: What is 25% of 200? Answer: (25 ÷ 100) × 200 = 50. This is used for discount calculations, tip amounts, tax computation, and more.
Percentage Change (Increase or Decrease)
Formula: ((New Value − Old Value) ÷ |Old Value|) × 100. A positive result means increase; negative means decrease. Example: price went from $80 to $100 — that's a 25% increase. This is essential for tracking price changes, growth rates, and performance metrics.
What Percent is X of Y?
Formula: (X ÷ Y) × 100. Example: 45 out of 60 = (45 ÷ 60) × 100 = 75%. Use this for test scores, completion rates, and proportional comparisons.
Percentage Difference
Formula: |V1 − V2| ÷ ((V1 + V2) ÷ 2) × 100. Unlike percentage change (which has a direction), percentage difference treats both values equally — useful for comparing measurements without a defined baseline.
Using Our Calculator
Select the calculation type from the tabs, enter your values, and get instant results with the formula shown. All calculations happen in your browser — no server, no signup, completely private.
Frequently Asked Questions
How do I calculate the percentage of a number?
Multiply the number by the percentage divided by 100. Example: 25% of 200 = 200 × (25÷100) = 50. Or divide by 100 first: 25% = 0.25, then 0.25 × 200 = 50.
How do I calculate percentage change?
Percentage change = ((New Value − Old Value) ÷ |Old Value|) × 100. A positive result is an increase; negative is a decrease. Example: $80 → $100 = ((100-80) ÷ 80) × 100 = 25% increase.
What is the difference between percentage change and percentage difference?
Percentage change has a direction (old→new) and a defined baseline (old value). Percentage difference treats both values equally and is used when there is no inherent 'before' and 'after'.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. Example: 45 is what % of 60? (45÷60)×100 = 75%.