Quick answer
Percent decrease = (old − new) ÷ old × 100. Falling from 80 to 60 is a 25% decrease, a difference of 20.
Enter the original and new values. The calculator returns the percentage decrease and the difference.
Related tools: Percent Increase Calculator: Percentage increase between two values. Reverse Percentage Calculator: Work backwards from a final amount to the original value before a percentage increase or decrease. Percent Difference Calculator: Symmetric percent difference between two values.
How to use the Percent Decrease Calculator
- Enter original value (above 0).
- Enter new value.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Original value | A number | > 0 |
| New value | A number | — |
Formula and method
Formula
decrease % = (old − new) ÷ old × 100
IEEE-754 double precision; shown to at most 6 decimal places.
The new value must be lower than the original; otherwise use the percentage change calculator.
Worked examples
This example is verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Original value = 80; New value = 60.
| Result | Value |
|---|---|
| Percentage decrease | 25 % |
| Difference | 20 |
The first line is the headline result (percentage decrease). Below it the percent Decrease Calculator lists difference, which describe the same case from other angles. IEEE-754 double precision; shown to at most 6 decimal places.
Asymmetry
A 25% decrease is not undone by a 25% increase: 60 × 1.25 = 75, not 80. To return to 80 you need a 33.3% increase. The base for each percentage is different.
Where this estimate stops applying
The original must be positive and the new value must be below it; for rises use the Percent Increase calculator. A fall to 0 is a 100% decrease.
How the result changes with original value
Holding every other input at the first worked example, this table changes only original value. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Original value | Percentage decrease | Difference |
|---|---|---|
| 80 | 25 % | 20 |
| 160 | 62.5 % | 100 |
| 320 | 81.25 % | 260 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Original value: entering "0" shows "Original value must be greater than 0." beside that field and no result.
- New value: entering "20" shows "The new value must be lower than the original." beside that field and no result.
Choosing between the Percent Decrease Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Percent Increase Calculator](/math/percent-increase-calculator/) | original value and new value | Percentage increase |
| [Reverse Percentage Calculator](/math/reverse-percentage-calculator/) | final amount, percentage applied and it was | Original amount |
| [Percent Difference Calculator](/math/percent-difference-calculator/) | value 1 and value 2 | Percent difference |
| [Percentage Change Calculator](/math/percentage-change-calculator/) | old value and new value | Percentage change |
| [Percent Off Calculator](/math/percent-off-calculator/) | original price and discount | Sale price |
Background: rounding and basic arithmetic
Rounding to a place looks at the digit just to its right: 0 to 4 rounds down and 5 to 9 rounds up (the half-up convention, so 2.5 becomes 3). Rounding 838.274 gives 800 to the nearest hundred, 840 to the nearest ten and 838 to the nearest one.
Some systems use banker's rounding (half to even), which sends 2.5 to 2 and 3.5 to 4; check which convention your task requires, and round only at the end of a multi-step calculation.
Assumptions and limitations
- Original must be positive
- New value must be below original
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for original value and new value to confirm this.
Frequently asked questions
What is a 50% decrease then a 50% increase?
A 50% fall then a 50% rise gives 1 × 0.5 × 1.5 = 0.75, a net 25% decrease.
How is percent difference different?
It uses the average as the base.
Can a decrease exceed 100%?
No. A decrease can reach 100% (the value falls to zero) but not exceed it for positive quantities.
What does the Percent Decrease Calculator calculate?
Percentage decrease between two values. It returns Percentage decrease and Difference.
What formula does the Percent Decrease Calculator use?
decrease % = (old − new) ÷ old × 100. The new value must be lower than the original; otherwise use the percentage change calculator.
What do I need to enter in the percent Decrease Calculator?
You enter Original value and New value.
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Original must be positive.
What are the limits of this calculator?
Original must be positive. New value must be below original.
What is an example of a percent Decrease result?
With original value 80 and new value 60, the percentage decrease is 25 %.
Related calculators
- Percent Increase Calculator — Percentage increase between two values.
- Reverse Percentage Calculator — Work backwards from a final amount to the original value before a percentage increase or decrease.
- Percent Difference Calculator — Symmetric percent difference between two values.
- Percentage Change Calculator — Find the percentage increase or decrease from an old value to a new value.
- Percent Off Calculator — Find the sale price and savings after a percentage discount.
- Percent Error Calculator — Compare a measured value with the true value.
- Decimal to Percent Calculator — Convert a decimal to a percentage.
- Percent to Fraction Calculator — Convert a percentage to a simplified fraction.
- Percent to Goal Calculator — Progress towards a target.
Sources
- OpenStax, Prealgebra 2e (Rice University): fractions, decimals, percents, ratios and rounding
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.