About this percentage calculator
Percentages show up everywhere — discounts, tax, tips, exam marks, interest. This page answers the three questions people actually ask: what is X% of a number, what percentage is one number of another, and by what percentage did a value increase or decrease.
How to use it
- Fill in any pair of boxes.
- Read its answer in the results table.
- Fill the other pairs too — all three answers update live.
The formula
X% of Y = Y × X/100\nPart as % = (Part / Whole) × 100\n% change = ((New − Old) / Old) × 100
Worked example
15% of 200 = 30. And 30 is 15% of 200. Going from 200 to 230 is a +15% change.
Frequently asked questions
How do I find the percentage increase?
Subtract the old value from the new one, divide by the old value, and multiply by 100. A rise from 200 to 230 is (30/200)×100 = 15%.
What is 20% of 45?
45 × 20/100 = 9. A quick mental trick: 10% of 45 is 4.5, so 20% is double that — 9.
Can a percentage be over 100%?
Yes. If a part is bigger than the whole — for example growth from 50 to 120 — the percentage is over 100% (that growth is 140%).