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By how much percent did a value change? This question comes up constantly with prices, salaries, visitor numbers or measurements - and it is a different one from the basic question of how much a percentage of a value is. From an old and a new value this calculator shows the percentage change, the absolute difference and the factor, that is the ratio of new to old. So you see an increase or decrease in percent at a glance.
The calculation runs entirely locally in your browser, in pure JavaScript - nothing is uploaded and nothing is stored. The percentage change is the difference between the new and old value, divided by the old value, times 100. A positive result is an increase, a negative one a decrease. The difference is new minus old, the factor is new divided by old - a factor of 1.25 equals plus 25 percent. The results are plain numbers; you set the unit yourself. Change an input and everything updates instantly.
An honest note: this is the percentage change between two values, not the basic percentage-of-a-value calculation - the percentage calculator handles that. If the old value is zero the change is undefined; the calculator then shows zero. The results are unitless numbers whose meaning you set yourself.
An important thinking trap this calculator makes visible: percentages are not symmetric. If a value falls by 50 percent and then rises by 50 percent again, it is not back at the start but 25 percent below it - because the second percentage refers to the smaller intermediate value. That is why, with ups and downs, prices or a discount on a discount, the reference value always decides.
Specifications
Specifications
Input formats
Form inputs (no file)
Processing
Locally in your browser (JavaScript)
File upload
None
In 3 steps
Enter the old value.
Enter the new value.
Read off the change, difference and factor.
Limitations: Percentage change between two values (not percentage of a value - use the percentage calculator). If the old value is zero the change is undefined (shown as zero). The results are unitless numbers whose meaning you set yourself.
FAQ
Are my inputs uploaded?
No. The calculation runs entirely locally in the browser (pure JavaScript); nothing is sent or stored.
How is the percentage change calculated?
(New value minus old value) divided by the old value, times 100. Example: from 80 to 100 is plus 25 percent.
What is the difference to the percentage calculator?
The percentage calculator answers "P percent of a value". This calculator answers "by how much percent did a value change" - a different question.
What does the factor mean?
New value divided by old value. A factor of 1.25 means plus 25 percent, a factor of 0.8 means minus 20 percent.