How do I calculate a percentage of a number?

Multiply the number by the percentage and divide by 100. For example, 20% of 150 equals 30.

How do I calculate percentage change?

Percentage change equals (New Value minus Old Value) divided by Old Value, times 100. A price going from 80 to 100 is a 25% increase.

What is the percentage difference formula?

Percentage difference equals the absolute difference divided by the average of the two values, times 100.

Percentage Calculator — % Of, Change, Discount & Tip

How to Use This Percentage Calculator

This calculator handles the three most common percentage questions in one tool. Use What is X% of Y? for calculating discounts, tips, and tax amounts. Use X is what percent of Y? to find a rate or ratio. Use Percentage change to calculate growth rates, price changes, and comparing two values over time. All results update instantly as you type.

The Three Core Percentage Formulas

Finding a percentage of a number: Multiply the number by the percentage expressed as a decimal. 15% of $240 = 240 × 0.15 = $36. This handles tips, discounts, commissions, tax calculations, and investment returns.

Finding what percentage one number is of another: Divide the part by the whole, then multiply by 100. If 35 out of 200 students passed, the pass rate is (35 ÷ 200) × 100 = 17.5%.

Percentage change: Subtract the old value from the new value, divide by the old value, multiply by 100. A stock that went from $48 to $63 increased by (63 − 48) ÷ 48 × 100 = 31.25%.

Real-World Uses for Percentages

Restaurant tips: 15% is standard, 18–20% is good, 20–25% is generous. On a $85 bill: 18% = $15.30; 20% = $17.
Sales tax: Average US combined sales tax is about 7.12%. A $299 item with 8% tax costs $299 × 1.08 = $322.92.
Discounts: A 30% discount on a $150 item = $150 × 0.30 = $45 off → final price $105. Or multiply: $150 × 0.70 = $105 directly.
Pay raises: A 4.5% raise on a $58,000 salary = $58,000 × 0.045 = $2,610 increase → new salary $60,610.
Investment returns: A portfolio that grew from $24,000 to $31,500 earned a 31.25% return.

Common Percentage Mistakes to Avoid

Percentages don't add symmetrically. A 50% drop followed by a 50% gain does NOT return you to the original value. Starting at $100, a 50% drop takes you to $50. A 50% gain on $50 only brings you back to $75 — you're still down 25%. This asymmetry is why investment losses are harder to recover from than people expect.

Percentage of a percentage. An interest rate that rises from 2% to 3% has increased by 1 percentage point, but by 50% in relative terms. Financial reporting uses both forms — make sure you know which one is being cited.

Frequently Asked Questions

How do I quickly calculate a 20% tip in my head?

Move the decimal one place left to get 10%, then double it for 20%. On a $73 bill: 10% = $7.30, doubled = $14.60. For 15%, find 10% ($7.30), take half of that ($3.65), and add them: $10.95.

What's the difference between percentage points and percent?

A percentage point is an absolute difference between two percentages. If unemployment rises from 4% to 6%, it rose by 2 percentage points — but by 50% in relative terms (2 ÷ 4 = 0.5). The distinction matters enormously in finance, economics, and politics where small changes in rates are reported both ways.

How do I find the original price before a discount?

If an item is marked down 25% and now costs $90, the original price was $90 ÷ (1 − 0.25) = $90 ÷ 0.75 = $120. Don't make the mistake of adding 25% back to $90 — that gives you $112.50, which is wrong.

% Percentage Calculator — 4 Modes