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Free Percentage Calculator

Work out percentages three ways: a percent of a number, what percent one value is of another, and the percentage change between two numbers.

FreeNo sign-upPrivate — runs in your browser, nothing is uploaded

Result
12
15% of 80 = 12

Quick answer

To find X% of a number, multiply the number by X ÷ 100. To find what percent A is of B, divide A by B and multiply by 100. To find the percentage change from an old value to a new value, subtract old from new, divide by the old value, then multiply by 100.

Formula & method

Percent of a number

result = number × (percent ÷ 100)
  • percent — the percentage you want, e.g. 15
  • number — the base value

What percent A is of B

percent = (A ÷ B) × 100
  • A — the part
  • B — the whole

Percentage change

change % = ((new − old) ÷ |old|) × 100
  • old — the starting value
  • new — the ending value

A positive result is an increase; a negative result is a decrease.

Common fractions as percentages

FractionPercentage
1/1010%
1/812.5%
1/520%
1/425%
1/333.33%
1/250%
2/366.67%
3/475%

Examples

Example 1: 15% of 80
Input
percent = 15, number = 80
Result
12
Why
80 × (15 ÷ 100) = 80 × 0.15 = 12.
Example 2: 30 is what percent of 120
Input
A = 30, B = 120
Result
25%
Why
30 ÷ 120 = 0.25, and 0.25 × 100 = 25%.
Example 3: Price rises from 50 to 65
Input
old = 50, new = 65
Result
+30%
Why
(65 − 50) ÷ 50 = 0.30, and 0.30 × 100 = a 30% increase.

When to use this tool

  • Working out a tip, discount, sales tax, or commission.
  • Comparing growth between two figures, such as revenue, weight, or a test score.
  • Checking what share one number is of a total.

Common mistakes

  • Confusing “percent of” with “percent change.” 20% of 50 is 10, but a 20% increase on 50 is 60.
  • Dividing by the new value when finding percentage change — always divide by the original (old) value.
  • Assuming a 50% drop and a 50% rise cancel out. They don’t: 100 → 50 → 75.

Assumptions

What the result takes for granted:

  • Both inputs are plain numbers in the same unit — the calculator doesn't interpret currencies or labels.
  • Percentage change is measured against the old (starting) value, not the new one.
  • For 'X is what % of Y', the whole (Y) must not be zero.

Limitations

Where this tool stops — and what to use instead:

  • A percentage on its own hides the base — a 50% rise on $2 is tiny next to 5% on $2,000.
  • Percentage points and percent are different: going from 10% to 12% is +2 points but a +20% change.
  • It calculates the math you ask for; choosing the right mode for your question is up to you.

Frequently asked questions

How do I calculate a percentage of a number?

Divide the percentage by 100 to turn it into a decimal, then multiply by the number. For example, 15% of 80 is 0.15 × 80 = 12.

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

Divide the part by the whole and multiply by 100. For example, 30 out of 120 is (30 ÷ 120) × 100 = 25%.

How do I calculate a percentage increase or decrease?

Subtract the old value from the new value, divide by the old value, and multiply by 100. A positive answer is an increase; a negative answer is a decrease.

What is the difference between percent and percentage points?

A percentage point is the absolute gap between two percentages. Going from 10% to 12% is a rise of 2 percentage points, but a 20% relative increase.

Why doesn’t a 50% increase cancel a 50% decrease?

Each percentage is taken from a different base. Starting at 100, a 50% drop gives 50; a 50% rise on 50 gives 75, not 100.

Is my input sent to a server?

No. This calculator runs entirely in your browser, so the numbers you enter never leave your device.

How do I calculate a percentage increase using this tool?

Use the '% change' tab. Enter the old value in the 'Old value' field and the new value in the 'New value' field. The tool will show you the percentage increase (positive) or decrease (negative).

Can I use this tool to calculate sales tax or tips?

Yes, for simple cases. Use the '% of a number' tab. Enter the tax/tip rate as the percentage and the purchase total as the number. For multi-rate taxes or more complex scenarios, a dedicated sales-tax-calculator or tip-calculator may be more convenient.

Sources & references

External references open in a new tab. We are independent and not affiliated with these organizations.

  • ✓ Free to use
  • ✓ No sign-up required
  • ✓ Runs entirely in your browser — nothing is uploaded.
  • ✓ Formula and method shown above
Last updated: How we calculateReport a correctionDisclaimer

Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.

Built and reviewed by HIFreeTools against the formula shown above and any authoritative references cited on this page. See our methodology and editorial standards.

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