Compare two prices
- Input or situation
- Percent change: old 120, new 150
- Result
- 25% increase
The increase is 30, and 30 ÷ 120 × 100 = 25. Comparing the same two prices in reverse gives a 20% decrease because the starting value becomes 150.
Math
Percentage calculator — change, of, and what percent
Check how much a value changed, add or subtract a percentage, or work out a share of a total. Choose the question that matches your task, then enter the known figures.
Runs in your browser — your input is not uploaded to ToolsNow.
The starting value.
The value after the change.
Fill in the fields above to see the result and its formula.
Percent change compares the new value to the original. Percent difference is not the same thing — it uses the average of the two values as its base.
How to use
- Percent change
- Enter an old and a new value in the same units. A price rising from €120 to €150 is a 25% increase; reversing those prices gives a 20% decrease.
- Apply %
- Enter a base and a percentage to see both outcomes. On €200, a 15% increase gives €230 and a 15% discount gives €170.
- X% of Y
- Find the amount represented by a percentage: 12.5% of €800 is €100.
- What % is X of Y
- Enter a part and its whole: 45 completed tasks out of 180 is 25%.
For a sale price you want to work backwards from, use the discount calculator and choose Original price.
Questions
How do I reverse a discount?
Divide the sale price by the proportion left after the discount. At 20% off, €80 is 80% of the original, so €80 ÷ 0.8 = €100. Adding 20% to €80 gives €96 because it uses the smaller sale price as its base.
Is percent change the same as percent difference?
No. For positive values, percent change uses the original as its base; percent difference uses their average and has no direction. From 150 to 120, the change is −20%, while the difference is 30 ÷ 135 × 100 ≈ 22.22%. Difference is therefore not always smaller. This page calculates change, not difference.
Why does a 50% rise followed by a 50% fall not return to the start?
Each percentage applies to a different starting amount. €100 rises 50% to €150, then falls 50% to €75. To undo the original rise, divide €150 by 1.5, which is equivalent to a fall of one third.
What if the starting value is zero or negative?
A percentage change from zero is undefined, so report the absolute change instead. For a negative start, this tool divides by the absolute value of the starting amount: −100 to −50 gives +50%. State that convention when reporting changes in losses or balances.
Examples and checks
Choose Percent change to compare an old value with a new one. Use X% of Y for a share of an amount, or Apply % to increase or reduce it.
Find a share
- Input or situation
- What % is X of Y: X = 45, Y = 180
- Result
- 25%
45 ÷ 180 × 100 = 25. For a discount of 25%, use Apply % instead: the discounted price is 75% of the original.
Before you use the result
- A change from zero has no finite percentage: report the absolute change instead.
- A rise from 100 to 150 followed by a 50% fall ends at 75. Each percentage applies to its own starting value.
Published by ToolsNow. How tools and sources are checked · Report a problem
Read more
Guide
How weighted grades and required final-exam scores are calculated Calculate a points-based or weighted grade, handle ungraded categories, and work out a required final-exam score using your course's actual rules.
Guide
How to scale a recipe without ruining it Work out a serving multiplier, handle fractions and partial eggs, and choose a suitable tin. What a scaled ingredient list changes and what still needs a decision.
Guide
How loan amortisation works: reading the payment and interest split Read an amortisation schedule, check the first two payments, and compare how a loan's rate and term affect monthly payments and total interest.
Related tools
Fraction calculator Add, subtract, multiply or divide fractions and simplify. Ratio calculator Simplify a ratio, see shares, and solve a : b = c : x. Average calculator Find the mean, median, mode and spread of a list of numbers. Number base converter Convert between binary, octal, decimal, hex and base 36. Roman numeral converter Numbers to Roman numerals and back, with validation. GCD & LCM calculator Greatest common divisor and lowest common multiple.