Percentage Calculator

How to use the percentage calculator

• X% of Y — enter a percent and a number to get the amount (e.g. 20% of 150 = 30).
• X is what % of Y — find what proportion one number is of another.
• Increase/decrease — enter a start and end value to see the percentage change.

The formulas

• Percentage of a number: (percent ÷ 100) × number
• What percent: (number ÷ total) × 100
• Percentage change: ((new − old) ÷ old) × 100

Everyday examples

• Discount: 25% off a $80 item → you save $20, pay $60.
• Tip: 15% of a $40 bill = $6.
• Grade: 45 out of 60 = 75%.

Benefits

• Answers the everyday percentage questions — "what is X% of Y", "X is what percent of Y", and percentage change — without memorizing formulas.
• Instant and mobile-friendly, so it works wherever you are.
• Shows the result clearly and, on the page, explains the formula so you learn it too.

Limitations to know

• It gives you the number, but understanding which calculation you need is still up to you — read the examples if you are unsure.
• Results are rounded to the displayed decimals.
• It is not built for compound growth across multiple periods — a dedicated finance calculator is better for that.

Common mistakes to avoid

• Confusing "percentage of" with "percentage change" — they answer different questions.
• Using the wrong starting value as the base when working out an increase or decrease.
• Mixing up percentage points with percent change (going from 10% to 12% is 2 percentage points, but a 20% increase).

Alternatives

For sale prices specifically, the Discount Calculator is quicker; for loan interest use the Loan Calculator; and for splitting a bill use the Tip Calculator.

Last updated: August 2026 · Reviewed by the AI Toolbox editorial team.

Frequently asked questions

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