Calculators & Time
Percentages, four ways
Four calculations that sound like one. Pick the question you are actually asking — the arithmetic differs, and so does the answer.
What do you want to work out
30
Percentage change is not symmetric: 100 to 150 is a 50% rise, but 150 back to 100 is a 33.3% fall. The starting value is always the denominator, which is the part that catches people out.
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How it works
Percentage change is not symmetric
Going from 100 to 150 is a 50% rise. Going back from 150 to 100 is a 33.3% fall, not 50%. The denominator is always the starting value, and mixing that up is the single most common percentage mistake — it is how a 50% discount followed by a 50% markup fails to get back to the original price.
"Of" and "is" are different questions
"What is 20% of 150" and "30 is what percent of 150" use the same three numbers in different roles. Offering them as separate calculations avoids the guessing that a single input box would require.
A change from zero has no percentage
Any increase from nothing is infinite in percentage terms. Rather than showing Infinity, the tool says so — because the honest answer is that the question does not have one.
What it does
Four calculations
Percentage of a number, one number as a percentage of another, change between two values, and adding or removing a percentage.
Add or remove
For discounts, markups, VAT and tips — the direction is a switch rather than a sign you have to remember.
Runs in your browser
No account and no upload — what you type is never sent anywhere. Analytics records that the tool was opened, never what you put into it.
Practical advice
Getting a better result
- A 20% discount then a 20% increase does not return the original price — it lands 4% lower, because the second percentage applies to a smaller number.
- To remove VAT rather than add it, use "remove" — dividing by 1.2 and subtracting 20% are different operations.
- Percentage points and percentages are not the same. Going from 10% to 15% is a rise of 5 percentage points and of 50%.
Questions
Things people ask
Why is the percentage decrease different from the increase?
Because the starting value changes. 100 to 150 divides the 50 difference by 100, giving 50%. 150 to 100 divides the same 50 by 150, giving 33.3%. Both are correct; they answer different questions.
How do I remove VAT from a price?
Use "remove" with the VAT rate. At 20%, removing it from £120 gives £96 — which is not the same as the £100 you would get by dividing by 1.2. Which one you want depends on whether the 20% was of the original or of the final price.
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