Example 1
- new = 100
- old = 80
25
What percent from 80 to 100? +25%.
Percentage change calculator
Type the new value and the old value. Percentage change says how far the new number moved from the old one, as a percent of that old number. From 80 to 100 you get +25%. From 100 to 80 you get −20%. Those are not mirrors, because the base changes.
The first field, a, is new. The second, b, is old. The formula is (a − b)/b × 100. When the old value is 0, the result is a blank result.
Results
Enter data and click Calculate.
How it works
Percentage change compares two states of one quantity. You subtract the old from the new, divide by the old, then times 100. From 80 to 100: (100 − 80)/80 × 100 = 25. From 100 to 80: (80 − 100)/100 × 100 = −20. A rise and a fall between the same numbers are not mirrors, because the denominator changes.
The new value is the first field, a. The old value is the second, b. The labels say that. 50 and 50 give 0, because nothing moved. 120 and 100 give +20. 40 and 50 give −20.
When the old value is zero, you divide by zero. The calculator returns a blank, not infinity. The form starts at zero and goes up, so you cannot type a negative amount here, even though the algebra would work the same on minuses.
This is not “percent of a number”. Percent of 80 is another calculator and another formula, with no old-new pair. Here you always have two states and one base: the old value.
The header currency switch does not multiply anything. 80 and 100 stay 25 whether the label says zloty or dollar. The unit cancels, and you are left with a percent.
From 200 to 250 is +25%. From 250 to 200 is −20%. From 10 to 15 is +50%. Going back from 15 to 10 is about −33.333.
Formula
(new − old) / old × 100, when old ≠ 0
How to use
- Type the new value, for example 100, and the old value, for example 80.
- Click Calculate. You get 25, a 25% rise.
- New 80 and old 100 give −20.
- Old 0 leaves a blank field.
- A percent of one number lives on another calculator. Here you always have an old and a new.
80 to 100 is +25%
Percentage change = (new − old)/old × 100. From 80 to 100 is +25%. From 100 to 80 is −20%. Old zero leaves a blank.
- new
- Field a, the state after the change. 100 with old 80 gives +25. 80 with old 100 gives −20.
- old
- Field b, the division base. 0 leaves a blank. 80 and 100 are not a mirrored plus and minus.
- percent
- The result in %. 25 from 80 to 100. 0 when both numbers match. This is not a percent of one amount.
Examples
Example 2
- new = 80
- old = 100
-20
And from 100 to 80? −20%, another base.
Example 3
- new = 50
- old = 50
0
Does the same number give 0%? Yes. Nothing moved.
Related calculators
Common questions
What percent from 80 to 100?
25. (100 − 80)/80 × 100 = 25. The base is 80, the old value.
Why is 100 to 80 not −25%?
Because the base is now 100. (80 − 100)/100 × 100 = −20. Same numbers, another denominator.
What does percentage change mean?
How far the new value moved from the old one, in hundredths of the old. Plus is a rise, minus is a fall.
Which field is new and which is old?
The first, a, is new. The second, b, is old. The formula is (a − b)/b × 100.
What if the old value is 0?
You do not divide by zero. The result is a blank result.
Do 50 and 50 give 0?
Yes. New equal to old is zero percent change, not an error.
How is this different from a percent of a number?
A percent of 80 takes a part of one amount. Here you always compare two states.
What about 200 to 250 and back?
From 200 to 250 is +25%. From 250 to 200 is −20%. Again, another base.
Does the header currency change the result?
No. 80 and 100 give 25 under every label. A percent has no currency.
What about 10 to 15?
50. (15 − 10)/10 × 100 = 50. From 15 to 10 is −33.333…, not −50.
Knowledge sources
The calculator computes the same formula as the definition below.
Page updated in 2026.