# Openoffice calc - Find out monthly growth based on yearly growth [closed]

I know there is a built-in function for that but can't remember what it is.

Let's say I have a number, `10`, and over a period of a year that number has increased by `100%` to `20`. I would like to figure out what the monthly increase should be for `10` to reach `20` over `12` months.

If I convert `100%` to a coefficient I get `2`. Now by trying several numbers manually I figured the monthly coefficient should be around `1.065`:

``````M.  NUMBER          COEFF
1   10              1.065
2   10.65           1.065
3   11.34225        1.065
4   12.07949625     1.065
5   12.8646635063   1.065
6   13.7008666342   1.065
7   14.5914229654   1.065
8   15.5398654581   1.065
9   16.5499567129   1.065
10  17.6257038992   1.065
11  18.7713746527   1.065
12  19.9915140051   1.065
``````

Q: How can I obtain the monthly coefficient (something around `1.065`) from `2` and `12`?

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## closed as off topic by Bruno Pereira, Jorge Castro, htorque, jokerdino♦, Nitin VenkateshAug 17 '12 at 9:17

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You may want to ask this over at math.stackexchange.com instead. – Christopher Kyle Horton Feb 1 '12 at 9:00

its more a mathematical question:

so over m months you want to multiply your value x by factor f. This can be written as follows (c = coefficient per month):

``````f * x = c*c*...*c*x
f * x = c^m * x
f     = c^m
c     = m-based root of f
``````

so in your example you can calculate it as:

``````c     = 11-based root of 2
``````

But - this is not a mathematical Q & A, i guess this topic will be closed soon ;)

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Thanks. do you happen to know the name of the function that corresponds to `m-based root of` ? – Max Feb 1 '12 at 9:01
"m-based root of x" = x ^ (1/m) - if i remember correctly it would be POW(x, (1/m)) – Michael K Feb 1 '12 at 9:03
Actually `calc` allows me to enter `x ^ (1/m)` directly. However if I do `2 ^ (1/12)` I get `1.0595...` which doesn't seem correct as after applying that coefficient I get `18.88` instead of `20` after a period of `12` months. – Max Feb 1 '12 at 9:09
you are right - there are only 11 increases - so it should be corrected to factor 11 ;) so use 11-th root – Michael K Feb 1 '12 at 9:12
You're the man :) – Max Feb 1 '12 at 9:19