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Everyday Math

Percentage Calculator

Result
30

Work out percentages three ways — a percent of a number, what percent one number is of another, and percent change.

By Sam T. · Reviewed by Dr. Lena Ortiz · Updated
Quick answer

To find a percent of a number, divide the percent by 100 and multiply by the number — 15% of 200 is 0.15 × 200 = 30. To find what percent one value is of another, divide the part by the whole and multiply by 100.

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How to use this calculator

  1. Pick the type of percentage problem from the dropdown.
  2. Enter the two values — labels update to match the mode you chose.
  3. Read the answer instantly; switch modes to check a different relationship.

Formula

P% of N = (P ÷ 100) × N · X/Y × 100 = % · (new − old) ÷ old × 100 = % change
  • P — percentage
  • N — base number
  • X, Y — the two values being compared

Worked example

What is 15% of 200? Multiply 0.15 × 200 = 30. Switching mode: 30 is 15% of 200, and going from 200 to 230 is a +15% change.

Frequently asked questions

How do I find a percent of a number?

Divide the percent by 100 and multiply by the number. For 15% of 200, that's 0.15 × 200 = 30.

How do I find what percent one number is of another?

Divide the part by the whole and multiply by 100. For example, 30 out of 200 is 30 ÷ 200 × 100 = 15%.

How is percent change calculated?

Subtract the old value from the new value, divide by the old value, then multiply by 100. A rise from 200 to 230 is (230 − 200) ÷ 200 × 100 = 15%.

What's the difference between percent change and percentage points?

Percent change is relative to the starting value; percentage points are the simple arithmetic difference between two percentages. Going from 10% to 15% is +5 percentage points but a +50% change.

How do I add or subtract a percentage from a price?

To add 8% tax, multiply by 1.08. To take 20% off, multiply by 0.80. The discount calculator handles markdowns directly.

Why is my percent change negative?

A negative result means the value decreased. Going from 230 down to 200 is about a −13% change.

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Sam T. · Author
Reviewed by Dr. Lena Ortiz · Updated 2026-06-03
Sources
Methodology · Report an error
Embed this calculator
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View answer.json (AI feed) 
{
  "tool": "percentage",
  "question": "How do you calculate a percentage of a number?",
  "answer": "To find a percent of a number, divide the percent by 100 and multiply by the number — 15% of 200 is 0.15 × 200 = 30. To find what percent one value is of another, divide the part by the whole and multiply by 100.",
  "formula": "P% of N = (P ÷ 100) × N    ·    X/Y × 100 = %    ·    (new − old) ÷ old × 100 = % change",
  "inputs": [
    {
      "id": "mode",
      "label": "What to calculate",
      "unit": null
    },
    {
      "id": "a",
      "label": "First value",
      "unit": null
    },
    {
      "id": "b",
      "label": "Second value",
      "unit": null
    }
  ],
  "sources": [
    {
      "name": "NIST — Mathematics & measurement basics",
      "url": "https://www.nist.gov/",
      "note": "Standard arithmetic definitions."
    }
  ],
  "updated": "2026-06-03"
}