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Percentage Calculator

Find percentages, compare a part to a whole, calculate percentage change, increase or decrease a value, and work backwards from an adjusted amount.

Your content stays on your device Free, with no account
Find the percentage. Check the calculation. Local calculation · no uploads
Use the exact field for any other supported percentage.
Display rounding only. Exact values remain available where the definitions are exact.

Use a decimal dot and optional scientific notation, without % signs or commas. Up to 120 digits, 180 characters and exponents −500 to 500. Percentage change needs a positive original value; division by a zero reference is undefined.

YOUR CALCULATION

Enter values to convert.

Percentage means per hundred. Exact arithmetic is applied before display rounding. Percentage points and relative percentage change are different quantities.

A FEW SIMPLE STEPS

How to use Percentage Calculator

  1. Choose a calculation: percentage of a value, part as a percentage of a whole, percentage change, adjustment or reverse adjustment.
  2. Enter the values shown. Use a decimal dot or scientific notation without commas or a % symbol. The quick slider covers 0–100%; the exact percentage field supports the full numeric limits.
  3. For adjustments, choose increase or decrease. Percentage change requires a positive original value; reverse decreases must be below 100%.
  4. Set significant digits with the slider or numeric input. Review the formula and exact result, then copy or download a TXT report.
PRIVATE BY DESIGN

Why use this tool?

All arithmetic happens locally in your browser. Your values are never uploaded, no account is needed and no input history is saved. Exact fractions avoid floating-point artifacts before display rounding, and the formula is shown so you can check the calculation.

Tool inputs stay in your browser. Only your theme preference is saved on this device.

A few things worth knowing

How do I calculate a percentage of a number?

Multiply the value by the percentage and divide by 100. For example, 15% of 200 is 30. Percentage-of mode supports signed values for arithmetic; adjustment modes use nonnegative values.

How do I find what percentage A is of B?

Divide the part A by the reference B and multiply by 100. For example, 30 is 15% of 200. B cannot be zero. Signed part/reference values are accepted as arithmetic, with the result sign preserved.

How is percentage change calculated?

The formula is (new − original) / original × 100. Going from 200 to 240 is a 20% increase. This mode requires a positive original value. Change from zero is undefined, and a negative original has ambiguous increase/decrease interpretation.

How do reverse percentages work?

Divide the final amount by 1 + P/100 for an increase, or 1 − P/100 for a decrease. A value of 120 after a 20% increase came from 100. A 100% decrease cannot be uniquely reversed, and this tool rejects reverse decreases of 100% or more.

Is a percentage-point difference the same as percentage change?

No. Moving from 10% to 15% is an increase of 5 percentage points but a relative increase of 50%. Enter 10 and 15 in Percentage change mode to calculate that relative change.

Why can the quick percentage slider be disabled?

The quick slider covers 0–100%. An exact value outside that range, an empty/invalid input or a value that cannot be represented faithfully by the slider disables it. The exact text field remains usable, including percentages above 100.

Are results rounded or stored?

The main display uses 2–12 significant digits and marks rounded values with ≈. Exact results, including repeating decimals or fractions, remain in the details. No input history is saved; only your theme preference is stored.

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