Percentage Calculator
Calculate a percentage, adjust a value or compare two values. Quick choices fill the percentage without replacing the base value.
Inputs allow a decimal point; comma decimals are also accepted in comma-decimal languages. No thousands separators. Zero is valid except as a divisor. Enter a complete decimal: at most 18 digits and 8 decimal places; no grouping or exponent.
Result
Change = (new − old) / |old| × 100; difference = new − old. A positive result means the value rose, even when the old value was negative.
Exact rational arithmetic precedes display rounded to at most 8 decimal places, ties away from zero. Tiny nonzero values use scientific notation; ≈ marks rounding. An exact whole result keeps all digits.
Method and limits
Percent of a value = value × percent / 100. Increase/decrease = value × (1 ± percent / 100). What percentage = part / total × 100.
Change = (new − old) / |old| × 100; difference = new − old. A positive result means the value rose, even when the old value was negative.
Exact rational arithmetic precedes display rounded to at most 8 decimal places, ties away from zero. Tiny nonzero values use scientific notation; ≈ marks rounding. An exact whole result keeps all digits.
Calculation stays in this page; values are not saved by the calculator. Copy sends only the current valid summary to the clipboard after your action. The site may load its usual scripts.
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About Percentage Calculator
Calculate a percentage, adjust a value or compare two values. Quick choices fill the percentage without replacing the base value.
These are dimensionless arithmetic scenarios. Use matching units for both values. Negative values and percentages over 100 are permitted; no tax, interest or market rule is inferred.
15% of 200 = 30; increasing 200 by 15% gives 230 and decreasing it gives 170. 30 out of 200 = 15%.
Arithmetic conventions only; no dated rate or jurisdiction is applied.
Use Cases
How to use
Choose a mode, then enter both labelled values. Results update as you type. Each mode keeps its own draft until you leave the page.
Inputs allow a decimal point; comma decimals are also accepted in comma-decimal languages. No thousands separators. Zero is valid except as a divisor.
Pro Tips
- Change = (new − old) / |old| × 100; difference = new − old. A positive result means the value rose, even when the old value was negative.
Frequently Asked Questions
The starting values differ: (100 − 80) / 80 = 25%, while (80 − 100) / 100 = −20%. A percentage change always needs a stated base.
The ratio is undefined. Enter a nonzero total in What percentage, or a nonzero old value in Percentage change; the page clears the previous result.