Percentage Calculator

What this calculator does

This calculator handles three common percentage problems. “Percent of a number” finds a portion of a value given a percentage. “What percent?” expresses one number as a fraction of another per hundred. “Percent change” measures how much a value has increased or decreased as a percentage of the original. All three modes use the same two input fields — only the interpretation and formula change.

Formulas

• X — percentage (Mode 1), value/part (Mode 2), or original value (Mode 3)
• Y — base number (Mode 1), total/whole (Mode 2), or new value (Mode 3)

How to use it

1. Select the mode that matches your question using the tabs.
2. Enter the two values in the fields — labels update to describe each input for the selected mode.
3. Click Calculate to see the result, input context, and (for percent change) the absolute difference.

Examples

• Mode 1: What is 15% of 200?
  (15 ÷ 100) × 200 = 30
• Mode 2: 30 is what percent of 200?
  (30 ÷ 200) × 100 = 15%
• Mode 3: % change from 200 to 230?
  ((230 − 200) ÷ 200) × 100 = +15%

What the result means

• Mode 1: The result is a portion of the base value — 30 represents 15 out of every 100 units of 200.
• Mode 2: The result is the ratio expressed per hundred. Values above 100% are valid and mean the part exceeds the whole.
• Mode 3: Positive = increase, negative = decrease. −100% means the value reached zero. The absolute change shows the raw numeric difference alongside the percentage.

Assumptions and limitations

• “What percent?” is undefined when the total (Y) is zero — there is no meaningful percentage of zero.
• “Percent change” is undefined when the original value (X) is zero — there is no percentage change from zero.
• Results are displayed to up to 4 decimal places with trailing zeros removed.
• Negative input values are accepted in all modes; results may be negative.