Everyone needs to know how to calculate percentages. Whether you’re splitting a restaurant bill or working out a discount in the sales, it’s a skill that comes up all the time. This guide shows you simple ways to work out percentages in your head, and if you just want a quick check, our free Percentage Calculator gives the answer in seconds.
Understanding how to calculate percentage
A percentage is just a fraction out of 100. So 25% means 25 out of 100, or 25/100, which is the same as 0.25. Nothing complicated about it—just a way to compare a part to the whole.
Imagine you spot a jumper with a 30% discount. The ticket price is £45. To work out the discount, start with 10% of £45. Move the decimal one place left, so that’s £4.50. Multiply that by 3 (because it’s 30%) and you get £13.50 off. The jumper then costs £31.50.
You can also turn the percentage into a decimal and multiply. For the same jumper, 30% as a decimal is 0.3. Multiply 0.3 by £45 and you get £13.50 straight away. The same method works for any percentage—just remember to shift the decimal in your head if you’re doing it without a pen.
How to work it out, step by step
- Enter the percentage (for example 15).
- Enter the number you want the percentage of.
- The answer appears instantly.
Result = (Percentage ÷ 100) × ValueWhy it matters
A slip in working out percentages can cost real money. I saw someone at a market price a £25 item at £30 after a discount. They’d calculated 20% of £25 correctly as £5, but then added it instead of subtracting it. Mistakes like that add up—whether you’re shopping, paying bills, or splitting a pizza, it’s worth double-checking your sums.
Free tools for this
| Tool | What it does |
|---|---|
| Percentage Calculator | Find a percentage of a number quickly and clearly. |
| Percentage Change Calculator | Find the percentage increase or decrease between two values. |
| Discount Calculator | Find the sale price and how much you save on any discount. |
Try the Percentage Calculator
Skip the manual maths — enter your numbers and get the answer instantly.
Open the Percentage Calculator →Good to know
Always double-check your inputs and units before trusting any result — a calculator is only as accurate as the numbers you give it. Writing out the formula once yourself also makes the method stick for next time.
Key takeaways
- Turn 10% of a number into a quick stepping stone—it’s just the number with the decimal moved one place left.
- For any percentage, divide by 10 to get 10%, then multiply by how many tens are in your percentage (e.g., 30% is 3 × 10%).
- Always ask yourself: am I adding or taking away the percentage? That’s where most people slip up.
Frequently asked questions
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. 30 out of 200 is (30 ÷ 200) × 100 = 15%.
Why doesn’t adding then subtracting 15% get me back to the start?
Because the second percentage is taken from a bigger number. 200 + 15% = 230, but 15% of 230 is 34.50, so you land on 195.50. Percentages are always relative to whatever base they are applied to.
How do I remove a percentage that is already included in a price?
Divide rather than subtract. A price that includes 20% tax is 1.2 times the net price, so divide by 1.2. Subtracting 20% would take too much off.
Do two discounts add up?
No. 50% off then 20% off means paying 0.5 × 0.8 = 0.4 of the original — a 60% discount, not 70%. Stacked percentages multiply.
Can I enter a percentage over 100?
Yes. 150% of 200 is 300. Percentages above 100 simply mean more than the whole.
