DavemiPercentage Calculator
Calculate percentages, increases, and decreases — instantly.
What is X% of Y?
X is what % of Y?
Percentage increase/decrease
Why use a percentage calculator?
Percentages look simple until the wording shifts — “15% of”, “is what percent of” and “increased by” are three different sums, and picking the wrong one quietly produces a plausible but wrong answer. Each mode here is labelled with the question it answers, so you pick the sentence that matches your problem rather than trying to remember which way round to divide.
How it works
- Choose the mode that matches your question.
- Enter your two numbers.
- Read the result, along with the working behind it.
- Adjust either value to compare scenarios instantly.
Frequently Asked Questions
How is percentage increase/decrease calculated?
It's the difference between the two values, divided by the original value, expressed as a percentage — a positive result means an increase, negative means a decrease.
How do I find X% of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 240 is 240 × 15 ÷ 100 = 36. The first mode on this page does it for you — enter the percentage and the number.
How do I work out what percentage one number is of another?
Divide the part by the whole and multiply by 100. If 37 people out of 250 replied, that's 37 ÷ 250 × 100 = 14.8%. Use the second mode and enter the two values in that order.
How do I calculate a discount or sale price?
Work out the discount amount as a percentage of the original price, then subtract it. A 30% discount on £80 is £24 off, leaving £56. You can also enter 70 as the percentage to get the final price directly.
What's the difference between percentage change and percentage points?
Percentage change is relative; percentage points are absolute. If a rate rises from 4% to 6%, that's a 2 percentage-point rise but a 50% increase. Mixing the two is the most common source of misleading statistics.
Why doesn't a 50% increase followed by a 50% decrease return the original number?
Because each percentage applies to a different base. 100 increased by 50% is 150; 50% of 150 is 75, so you land at 75, not 100. To reverse a 50% rise you need a 33.3% fall.
How do I add or remove sales tax or VAT?
To add 20% tax, multiply by 1.2. To remove it, divide by 1.2 — don't subtract 20%, which gives the wrong answer. Removing 20% VAT from £120 gives £100, whereas subtracting 20% would wrongly give £96.
How do I calculate percentage error?
Take the difference between the measured and true value, divide by the true value, and multiply by 100. The result is usually reported as an absolute figure, ignoring the sign.
Can I use it for grades and test scores?
Yes. Enter the marks you scored as the part and the total available as the whole to get your percentage. The same mode works for any 'X out of Y' figure.
Is my data uploaded anywhere?
No. All calculations run locally in your browser — nothing is sent to a server.
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