# Simple Math Question
**URL:** https://boards.straightdope.com/t/simple-math-question/380130
**Category:** Factual Questions
**Created:** [November 12, 2006, 6:23pm UTC](https://boards.straightdope.com/t/simple-math-question/380130 "2006-11-12T18:23:44Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@TheBoneyKingofNowhere](https://boards.straightdope.com/u/TheBoneyKingofNowhere)
#### Post date: [November 12, 2006, 6:23pm UTC](https://boards.straightdope.com/t/simple-math-question/380130/1 "2006-11-12T18:23:44Z")
Calculating a percent change in something. Say population of an area between year 1 and 2. When year two is greater than year 1, simple enough:
Year 1: 2000
Year 2: 2500
(2500/2000) -1 = 25% increase.
But what if the difference between year 1 and 2 is negative?
Year 1: 2500
Year 2: 2000
. . Is it (2000/2500)-1 = -20%
.or is it (2500/2000)-1)/-1 = -25% (like the inverse of the increase of 25%)?
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### Author:  [@Giles](https://boards.straightdope.com/u/Giles)
#### Post date: [November 12, 2006, 6:26pm UTC](https://boards.straightdope.com/t/simple-math-question/380130/2 "2006-11-12T18:26:55Z")
IMHO, it’s a 20% decrease, because it’s calculating from the starting point.
Population of 2 going to 1 is a 50% decrease, and not a 100% decrease.
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### Author:  [@Alive\_At\_Both\_Ends](https://boards.straightdope.com/u/Alive_At_Both_Ends)
#### Post date: [November 12, 2006, 6:27pm UTC](https://boards.straightdope.com/t/simple-math-question/380130/3 "2006-11-12T18:27:24Z")
It’s a 20% decrease. You always use the first figure (here 2500) as the base figure when calculating percentage changes.
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### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [November 12, 2006, 8:48pm UTC](https://boards.straightdope.com/t/simple-math-question/380130/4 "2006-11-12T20:48:13Z")
One of the key side effects here is that after taking a 20% pay cut, it takes a 25% pay raise to get back to the original rate.