# Thread: Exponential Decline From Input Box

1. Registered User
Join Date
Jun 2005
Location
Denver, CO
Posts
100

## Unanswered: Exponential Decline From Input Box

I have a large number that a need to make decline exponentially 12 times (12 months) based on a percentage from an input box. I'm rasing the percent decline to the power of .1 ((1-X%)^.1) but this does not seem correct. Any sugestions? Thanks!

2. Registered User
Join Date
Apr 2004
Location
Derbyshire, UK
Posts
804
Hi

I think (pehaps) you need somthing like this (for a Decline)

Number*EXP(-Pct*MonthNumber)

where

Number = number to decline (fixed)
Pct = fixed percentage (as a decimal!)
MonthNo = 1 to 12

??

MTB

3. Registered User
Join Date
Jun 2005
Location
Denver, CO
Posts
100
I think that's what I want. What would you do if you wanted a 70% decline total in year one?

4. Registered User
Join Date
Apr 2004
Location
Derbyshire, UK
Posts
804
Hi again

Still not sure what you are doing, but declining exponetially on a monthly basis by 70% in 12 months (ie to 30% of start value) is given by

Number*EXP(-Factor*MonthNumber)

where

Number = number to decline (fixed)
Factor = = 0.1
MonthNo = 1 to 12

??

MTB

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