Calculate a Percentage of a Number: Simple Online Calculator

Use this calculator to do the five most common percent tasks in seconds: A% of B, What % is A of B?, Increase/Decrease by A%, and % change from A to B. It’s fast, accurate, and built for everyday work, study, and life.

Calculate a Percentage of a Number

Fast, accurate percentage math with rounding and copy-to-clipboard.

Choose a calculation

Mode

A (percent or first value)

B (base or second value)

Quick percent

Rounding

Formatting

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What this calculator does

A% of B — find the portion of a number (e.g., “15% of 250”).
What % is A of B? — compare two values as a percentage (e.g., “23 is what % of 80?”).
Increase B by A% — add a percentage to a base number (e.g., “increase 799 by 8%”).
Decrease B by A% — subtract a percentage from a base (e.g., “decrease 120 by 15%”).
% change from A to B — measure relative growth or drop between two values (e.g., “from 120 to 144”).

Options include rounding (0/2/4 decimals) and formatting (locale or plain). You can also tap Quick percent chips to fill common rates instantly.

How to use it

Choose a calculation from the Mode dropdown.
Enter A and B in the labeled fields (labels adapt to the mode).
(Optional) Pick your rounding and formatting preferences.
Click Calculate to see the result, formula, and the rounding used. Use Copy result to put the output on your clipboard.

Calculate a Percentage of a Number: Simple Online Calculator

We wish you a small percentage of the loan, and a large percentage of profit

Examples & real-world uses

1) A% of B

Use it for tips, commission, discounts, taxes, allocation, etc.

Example: 18% of 64.50 → (18 ÷ 100) × 64.5 = 11.61. A typical restaurant tip.
Example: 6.5% of 1,200 → 78. Sales tax or platform fee.
Example: 25% of 3,200 → 800. Quarterly allocation of a monthly budget.

2) What % is A of B?

Perfect for progress reports, exam scores, or contribution shares.

Example: 23 is what % of 80? → (23 ÷ 80) × 100 = 28.75%.
Example: 450 of 1,250 → 36%. Portion of total signups from one channel.
Example: 17 of 20 → 85%. Test result.

3) Increase B by A%

Use it for markups, raises, inflation adjustments, forecast growth, indexation.

Example: Increase 799 by 8% → 799 × (1 + 8/100) = 862.92.
Example: Increase 2,100 by 3.5% → 2,173.5. Annual price index update.
Example: Raise of 12% on 5,000 → 5,600.

4) Decrease B by A%

Use it for discounts, depreciation, churn, efficiency gains.

Example: Decrease 120 by 15% → 120 × (1 − 15/100) = 102.
Example: Decrease 1,450 by 20% → 1,160. Promotion price.
Example: Decrease 300 by 2.5% → 292.5. Waste reduction target.

5) % change from A to B

Use it for month-over-month metrics, profit deltas, KPI dashboards, personal goals.

Example: From 120 to 144 → ((144 − 120) ÷ 120) × 100 = 20% increase.
Example: From 50 to 37.5 → −25% decrease.
Example: From 10,000 to 10,600 → 6% growth.

Formulas (shown in the app)

A% of B = (A ÷ 100) × B
What % is A of B? = (A ÷ B) × 100
Increase B by A% = B × (1 + A/100)
Decrease B by A% = B × (1 − A/100)
% change from A to B = ((B − A) ÷ A) × 100

Rounding and formatting

Rounding: choose 0, 2, or 4 decimals. Financial figures often show 2 decimals; engineering/science may use 4.
Formatting: “Auto (your locale)” uses your device’s separators (e.g., 1,234.56 vs 1 234,56). “Plain” removes grouping for easy copy into spreadsheets or code.
The calculator performs the math at full precision, then applies your rounding to the display.

Tips & best practices

Know what the percent applies to: “15% off 80” means decrease; “15% of 80” means a portion. They’re different numbers (68 vs 12).
Use “What % is A of B?” when you need contribution shares or grades.
Use “% change” for before/after comparisons (e.g., traffic, revenue, weight, time).
Decimals vs whole numbers: 7.5% is valid. The tool supports decimals in both percent and base.
Zero rules: “What % is A of B” needs B ≠ 0. “% change” needs A ≠ 0 (otherwise change relative to zero is undefined/infinite).

Example scenarios

Shopping: A jacket is $120 with 25% off → decrease 120 by 25% = $90.
Tips: 18% of 64.50 = $11.61.
Analytics: Signups from campaign A are 450 of 1,250 → what % is 450 of 1,250 = 36%.
Budgeting: Increase the rent fund 3% yearly → increase 1,800 by 3% = 1,854.
Fitness: From 180 to 165 → % change = −8.33%.

Note: This tool runs entirely in your browser and is absolutely private. No data is sent anywhere. Results depend on the numbers you provide and the rounding you choose.