Percentage Calculator
Five common percentage operations: percent of, ratio, change, increase, decrease. Live result as you type.
What is X% of Y?
Result
Enter both values to see the result
Five percentage operations in one tool: % of, ratio, change, increase, decrease. Live result as you type.
Percentage Calculator answers the five most common percentage questions in one tool: What is X% of Y? · X is what percent of Y? · What is the percent change from X to Y? · X increased by Y%? · X decreased by Y%? Pick a mode, type two numbers, see the result instantly.
Use it for: shopping discounts (15% off $80?), tip calculations, grade calculations (35 out of 50 = 70%), markups, sales tax (8% of $19.99?), salary raises (5% increase from $60k?), revenue growth (Q1 → Q2 change), and any math homework involving percentages.
Free, no signup, browser-side. Pure JavaScript math — handles decimals to 6 places, negative numbers, and large values without precision loss for typical inputs.
Key features
- 5 operation modes — X% of Y · X is what % of Y · % change · X increased by Y% · X decreased by Y%. Switch instantly with one-click tab.
- Live result — Result updates as you type — no 'calculate' button needed.
- Handles negatives + decimals — Negative percent change (drop), decimal percentages (12.5%), and large numbers all work.
- Direction indicator for % change — Shows ↑ Increase / ↓ Decrease arrow with the percentage.
- Browser-side only — Inputs and results stay in your tab. No tracking, no signup.
How to use
- Step 1: Pick the operation — Five tabs at the top. Most common: '% of' (sales tax / discount) or '% change' (growth).
- Step 2: Type two numbers — First field varies by mode (percentage, value, or starting number). Second field is the second value.
- Step 3: Read the result — Result appears in the blue panel below as you type. Copy-paste straight into your spreadsheet or email.
When to use
- Shopping discount: 'X% of Y' mode — 25% off $120 = $30 saved
- Tip calc on a receipt: 'X% of Y' — 18% of $47 = $8.46
- Grade calc: 'X is what % of Y' — 38/50 = 76%
- Salary raise: 'X increased by Y%' — $80,000 + 5% = $84,000
- Quarterly growth: '% change' — Q1 $1.2M → Q2 $1.5M = +25%
- Sale price math: 'X decreased by Y%' — $200 − 30% = $140
- Markup pricing: 'X increased by Y%' — $50 cost + 60% markup = $80 sell price
Frequently asked questions
What's the difference between % change and increase/decrease?
% change tells you the PERCENT (e.g., '+25%') given two values. Increase/decrease tells you the new VALUE (e.g., $230) given a starting value and a percent. They're inverses.
How do I calculate tax-inclusive vs tax-exclusive price?
Tax-inclusive: '$100 includes 10% tax — what was the pre-tax price?' Use 'X is what % of Y': you know $100 = 110% of pre-tax, so pre-tax = $100 / 1.10 = $90.91. (Or use 'decrease' mode: $100 decreased by 9.09% = $90.91.) Native tax-inclusive mode is on the roadmap.
Can it do percentage-point math (different from percent)?
Not directly — percentage points (e.g., '5% to 8% is +3 pp, not +60%') need subtraction, not percentage math. Use a regular calculator for pp.
Precision limits?
JavaScript Number is double-precision float — safe for ~15 significant digits. For typical money / tax / discount math, precision is exact. Very large numbers (>10^15) lose precision in the last digit.
What if my percent is greater than 100 (or negative)?
Works correctly: 150% of 200 = 300; -10% of 50 = -5; -20% increase = decrease by 20%. The tool doesn't restrict ranges.
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