What is 15% of 30?
15% of 30 is 4.5. Use the calculator below to change either number, or see related calculations.
Calculating 15% of 30: divide 15 by 100, then multiply by 30. The general formula is (X ÷ 100) × Y — works for any percentage and any number.
Percentages around this level appear in everyday calculations (interest rates, growth, splits). This base value sits in the everyday range — receipts, tips, small purchases.
How it works.
Formula: (X ÷ 100) × Y.
Step by step:
- Divide the percentage by 100: 15 ÷ 100 = 0.15.
- Multiply by the number: 0.15 × 30 = 4.5.
Worked examples
15% of 30 = 4.5 — the basic calculation: divide 15 by 100 (= 0.15), then multiply by 30.
15% of 30 as a tip on a small bill — if a service charge of 15% is added to a 30 item, the extra is 4.5.
15% off a 30-pound item — the discount saves 4.5; the sale price is £25.5.
Frequently asked questions
How do I calculate 15% of 30?
Divide 15 by 100, then multiply by 30. 15 ÷ 100 = 0.15; 0.15 × 30 = 4.5. The same formula works for any pair of numbers.
What is 15 percent of 30?
4.5. The full calculation: (15 ÷ 100) × 30 = 0.15 × 30 = 4.5.
Are there mental-maths shortcuts for percentages?
Yes. 10% of any number is the number with the decimal moved one place left. From there: 20% is double 10%; 5% is half of 10%; 15% is 10% plus half of 10%; 25% is a quarter; 50% is half. For UK shopping discounts, the 10%-anchor trick covers most quick estimates without a calculator.