EVERYDAY MATH
Percentage calculator
Calculate percent of a number, part of whole, percentage change and add-or-subtract percentage scenarios.
Neutral presentation is active.
No regional currency, unit or language profile is applied. This choice does not convert values or change formulas, results, routes or legal guidance.
Percentage result
3015% of 200 = 30- Part of whole
- 25 is 12.5% of 200
- Percentage change
- 25% increase
- Add percentage
- 200 + 15% = 230
- Subtract percentage
- 200 − 15% = 170
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Verification and calculation details
- Purpose
- Percentage calculator
- Variables and units
- Use the labelled fields and units shown in the calculator. Results use those units unless a conversion is stated.
- Formula and method
- The exact formula and worked example are shown below. Deterministic formula executed locally in the browser.
- Assumptions
- Only entered values and stated assumptions are included. Local fees, rules and professional requirements are excluded unless explicitly shown.
- Engine version
- 1.0.0
- Production verification baseline
- Release 63 · source
998803f - Verification run
release-v63-2026-09-20- Last verified
- — Automated release checks passing
Read the Calculation Standard · Report a calculation or source issue
How this calculator works
Percentage value = base value × percentage ÷ 100. Part of whole = part ÷ whole × 100. Percentage change = (new value − old value) ÷ old value × 100.
Variables and inputs
- Value
- Required numeric input. finite numeric value; calculator-specific validation applies.
- Percentage
- Optional numeric input. finite numeric value; calculator-specific validation applies.
- Part
- Optional numeric input. finite numeric value; calculator-specific validation applies.
- Whole
- Optional numeric input. finite numeric value; calculator-specific validation applies.
- Starting value
- Optional numeric input. finite numeric value; calculator-specific validation applies.
- Ending value
- Optional numeric input. finite numeric value; calculator-specific validation applies.
How to interpret the result
The calculator returns percentage of a value, percentage represented by a part, percentage change, value after percentage increase, value after percentage decrease. Read each output against the assumptions you entered, compare alternatives one variable at a time, and use the result as an estimate rather than a promise.
Common mistakes to avoid
- Mixing units or entering a rate as a decimal when the field requests a percentage.
- Rounding intermediate values instead of the final displayed result.
- Leaving out a cost, timing rule or local requirement listed in the assumptions below.
Practical uses
Use the percentage calculator to check a real scenario, compare a changed assumption and explain the arithmetic before relying on a quote, specification or decision.
Worked example
15% of 200 is 30. If a value moves from 120 to 150, the percentage change is 25%. Adding 15% to 200 gives 230, while subtracting 15% gives 170.
Assumptions and limitations
- percentage-change calculations use the original value as the denominator
- increase and decrease operations apply the entered percentage once without compounding
- results are estimates; confirm rates, prices, units and professional requirements that apply
Important notes
Results are estimates based on the values entered. Confirm rates, prices, units and professional requirements that apply in your location. Review the Answer Atlas Calculation Standard and corrections policy for formula, privacy and correction rules.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage, then divide the result by 100.
How do I work out what percent one number is of another?
Divide the part by the whole, then multiply by 100. The whole must be above zero.
How do I calculate percentage increase or decrease?
Subtract the old value from the new value, divide by the old value, then multiply by 100. A positive result is an increase and a negative result is a decrease.