This calculator is for informational purposes only and does not constitute medical advice. Results are estimates based on general formulas. Consult a qualified healthcare professional before making health decisions.
Percentage Calculator
Three ways to calculate percentages — instantly.
What is X% of Y?
📐 Percentage Formulas
- X% of Y = (X / 100) × Y
- X is ?% of Y = (X / Y) × 100
- % Change = ((New − Old) / |Old|) × 100
🔢 Common Percentages
Percentages show up in retail discounts, tax brackets, tipping, statistics, and finance — and the three operations look similar but mean different things. The calculator covers all three: percentage of, percent change, and percent difference.
Three percentage formulas
Percentage of a number: (X / 100) × Y. So 20% of 80 = 0.20 × 80 = 16. Percent change: (new − old) / old × 100. From 50 to 75 is +50%, from 75 to 50 is −33%. Percent difference (symmetric): |a − b| / ((a + b) / 2) × 100. Use this when neither value is the baseline.
When to use this calculator
Use 'percentage of' for tips, sales tax, and discount calculations. Use 'percent change' for tracking growth — revenue, weight, anything with a clear before-and-after. Use 'percent difference' when comparing two measurements that don't have a 'first' (the diameter of two pipes, the height of two people).
Worked example
A laptop drops from $1,200 to $999. Percent change: (999 − 1,200) / 1,200 × 100 = −16.75%. Percent difference: |1,200 − 999| / ((1,200 + 999) / 2) × 100 = 18.3%. Different numbers, both correct — they answer different questions.