What is 15% of 30?
15% of 30 is 4.5. A quick mental check is 10% (3) plus 5% (1.5).
The answer is 4.50.
Result Explanation
15% of 30 = 4.5. If you mean 15% off 30, then 4.5 is the discount and the new total is 25.5. For that workflow, use the discount calculator.
If you’re comparing two totals (not taking a slice), use the percentage change calculator. For reverse problems, use the reverse percentage calculator.
How It Works
Step 1: Convert 15% to a decimal by dividing by 100. That gives 0.15.
Step 2: Multiply the decimal by the number: 0.15 × 30 = 4.5.
Full formula: (15 ÷ 100) × 30 = 4.5
This method works for any percentage-of-number calculation and is the most reliable way to get an exact answer.
Strategy & Insight
A fast way to estimate 15% mentally is to split it into 10% + 5%. For 30, 10% is 3 and 5% is 1.5. Add them together and you get 4.5.
This is a good example of why 15% is a useful working percentage. It is common enough to show up in real decisions, but simple enough to break into smaller familiar parts. On a number like 30, the mental route is nearly as fast as using a calculator, which makes it ideal for checking discounts or charges on the spot.
Common Mistakes
- Using 15 instead of 0.15 when multiplying.
- Answering with the reduced total of 25.5 instead of the percentage amount of 4.5.
- Ignoring that 4.5 is the same as £4.50 in a money example.
- Rounding too soon when you need a precise financial result.
- Confusing “15% of 30” with “30 increased by 15%”.
Pro Tip
When the base amount is 30, it is usually faster to think in chunks than to start from scratch. Find 10%, find 5%, then combine them. This reduces errors and makes mental checking much easier.
Examples
Example 1: Discount on a £30 item
If a product costs £30 and has a 15% discount, the saving is £4.50. The final price becomes £25.50.
Example 2: Small service fee
If a platform fee is 15% on a £30 transaction, the fee amount is £4.50.
Example 3: Budget allocation
If you set aside 15% of £30 for transport, savings, or testing spend, the reserved amount is £4.50.
Related Calculations
FAQ
What is 15% of 30?
15% of 30 is 4.5.
How do you work out 15% of 30?
Convert 15% to 0.15 and multiply it by 30. The answer is 4.5.
What is 15% off 30?
15% off 30 is a reduction of 4.5, leaving a final amount of 25.5.
What is the fastest mental method for 15% of 30?
Find 10% of 30 first, which is 3, then add 5%, which is 1.5. Together they make 4.5.