To find X percent of Y, multiply Y by X ÷ 100: 20% of 250 is 50. To find a percentage change, divide the difference by the original value: from 80 to 100 is +25%. A decrease of 20% followed by an increase of 20% does not return you to the start, because the second percentage applies to a smaller number.
The five percentage calculations
| Question | Formula | Example |
|---|---|---|
| X% of Y | X ÷ 100 × Y | 20% of 250 = 50 |
| X is what % of Y | X ÷ Y × 100 | 45 of 60 = 75% |
| Change from X to Y | (Y − X) ÷ X × 100 | 80 → 100 = +25% |
| Increase X by Y% | X × (1 + Y ÷ 100) | 200 + 15% = 230 |
| Decrease X by Y% | X × (1 − Y ÷ 100) | 200 − 15% = 170 |
Percentage decrease and why it is asymmetric
Percentages always refer to a base. If a price falls from €100 to €80, that is a 20% decrease. To get back to €100 you need a 25% increase, because the increase applies to €80. This asymmetry grows with size: a 50% loss needs a 100% gain to recover. The calculator’s change mode adds a note with the recovery percentage for any decrease, which is useful when thinking about investment losses.
Percentages in everyday life in the Netherlands
- BTW: adding 21% means multiplying by 1.21, but removing it means dividing by 1.21. See the BTW calculator.
- Discounts: “30% korting” on €89.95 is 89.95 × 0.70 = €62.97. Combined discounts multiply, so 20% then 10% off is 28% in total, not 30%.
- Salary raise: a 3% raise on €3,500 gross gives €3,605, see your net effect in the salary calculator.
- Interest and inflation: the compound interest calculator applies percentage change repeatedly.
Percentage points versus percent
If the interest rate rises from 3% to 4%, it has gone up by one percentage point, but by 33% in relative terms. News reports mix them up, which is why it pays to ask what the base is. For lists of numbers use the average calculator instead.
How to use this calculator
- Choose the type of percentage question from the list.
- Enter X and Y. The labels in the result remind you what each number means.
- Read the answer and the formula used.
- Try the reverse calculation to check your result.
Key figures at a glance
| X% of Y | X ÷ 100 × Y |
|---|---|
| Change | (new − old) ÷ old × 100 |
| Add percentage | × (1 + p) |
| Remove percentage | × (1 − p) |
Frequently asked questions
Divide the percentage by 100 and multiply by the number. 15% of 80 is 0.15 × 80 = 12.
Subtract the old value from the new value, divide by the old value and multiply by 100.
Use (old − new) ÷ old × 100, or multiply the original by (1 − p) to get the new value.
The second percentage applies to the reduced amount. 100 − 20% = 80, and 80 + 20% = 96.
A rise from 3% to 4% is one percentage point but a 33% increase.