Belgium
Percentage calculator
Three percentage jobs sit behind one tool. Find a percentage of a number, find what percentage one number is of another, or measure the increase or decrease between two figures. Enter the two values for whichever calculation you need and read the answer straight off. It suits everyday sums: a shop discount, a tip, the VAT share of a price, a test score, a deposit as a fraction of a salary, or quarter-on-quarter growth at work. No rounding tricks, just the plain arithmetic shown step by step.
How it works
- Percentage of a number: multiply the number by the percentage, then divide by 100. So 15% of 200 is 200 x 15 / 100 = 30.
- One number as a percentage of another: divide the part by the whole and multiply by 100. 30 out of 200 is (30 / 200) x 100 = 15%.
- Percentage change: take the new value minus the old, divide by the old, multiply by 100. Going from 200 to 250 is (50 / 200) x 100 = a 25% rise.
- A negative change result means a decrease. From 250 down to 200 gives minus 20%.
part = (p / 100) x whole ; p% = (part / whole) x 100 ; change = ((new - old) / old) x 100
All three jobs share the same idea, that a percentage is a fraction out of one hundred. To find a percentage of a number, turn the percentage into a fraction and multiply. To express one number as a percentage of another, divide the smaller part by the whole and scale by 100. For a change, compare the gap between the two values against the value you started from.
- p
- the percentage figure, for example 15 for fifteen percent
- whole
- the base or total the percentage is taken from
- part
- the slice being compared to the whole
- old, new
- the starting and ending values in a change
Percentages you meet often
| UK standard VAT rate | 20% | the tax share added to most goods and services |
| Customary restaurant tip | 10% to 15% | of the bill before service charge |
| Typical mortgage deposit | 10% to 25% | as a fraction of the property price |
| Pass mark on many UK exams | 40% to 50% | marks gained out of the total available |
| A half, a quarter, a tenth | 50%, 25%, 10% | the fractions behind everyday splits |
Worked example
A 200 item reduced by 15% cuts 30 off the price, leaving 170. Read the other way, 30 is 15% of 200, and the move from 200 to 170 is a 15% decrease. The same three operations cover all of it.
Key facts
- A percentage is just a fraction with 100 as the denominator, so 37% means 37 out of every 100.
- Finding a percentage of a number and finding what percentage one number is of another are inverse operations.
- A percentage change can run past 100% when the new value is more than double the old one.
- Order does not matter when you multiply, so 8% of 50 equals 50% of 8, both giving 4.
Tips
- To take a quick 10%, slide the decimal point one place left; 10% of 340 is 34, and 5% is half of that, 17.
- Adding then removing the same percentage does not cancel out, because the second step works on a different base, so reverse a discount by dividing rather than subtracting.
- For a tip in your head, find 10% of the bill, halve it for 5%, and add the two to reach 15%.
- When a figure is quoted as up by some percent, keep the original value to hand, since every later change is measured against a new base.
A percentage of 200, at several levels
| Percentage | Of 200 | As a fraction |
|---|---|---|
| 5% | 10 | one twentieth |
| 10% | 20 | one tenth |
| 25% | 50 | one quarter |
| 50% | 100 | one half |
| 75% | 150 | three quarters |
| 150% | 300 | one and a half times |
Frequently asked questions
How do I add a percentage on top of a number?+
Multiply by one plus the percentage written as a decimal. Adding 20% to 50 is 50 x 1.20 = 60. To take 20% off instead, multiply by 0.80.
Why is a rise then an equal fall not back to the start?+
Because each percentage applies to a different base. 100 up 10% is 110, then down 10% is 99, not 100. The fall is measured against the larger 110.
What is the difference between percent and percentage points?+
A shift from 10% to 12% is 2 percentage points, yet a 20% relative increase on the starting 10%. Mixing the two is a common reporting error.
Can I reverse a discount to find the original price?+
Yes. If a price after 20% off is 80, divide by 0.80 to recover the original 100. Dividing undoes the multiplication.
Things to watch
- Percentage points and percent are not the same; a move from 4% to 6% is two percentage points but a 50% relative rise.
- Stacked percentages do not add, so a 20% discount followed by a further 10% off is 28% off in total, not 30%.
- These are arithmetic results, not financial advice; a real price, loan or tax figure may carry rounding rules or fees that change the final number.
Last updated: 2026-01-01
This is an estimate for general guidance, not financial, tax, legal or medical advice. Figures can change and individual circumstances vary. Always confirm with the official sources listed before making decisions.
- Calculations are exact; any rounding you see is only in how the answer is displayed.
- Percentage change needs a non-zero starting value, since dividing by zero is undefined.
Reviewed by Vikas Dulgunde.