Hi Ken!
If your equipment cost $2000 and the annual saving was 50 per month
for 60 months
=(1+RATE(60,50,-2000,0,0))^12-1
Returns: 18.7091167089518% per annum effective
The key bit here is:
=RATE(60,50,-2000,0,0)
Which on it's own returns: 1.43947810009151%
This reflects money out (hence negative 2000) at the beginning. Money
comes in (hence positive 50) for 50 periods with a zero final value
and assuming you wait until the end of the first month for your
return.
Since I'm measuring time in months the RATE function returns the rate
per month. I therefore "nest" the function in the compound interest
formula (1+i)^n-1
It's all based upon assumptions. In your case there's an assumption
that the return will not increase or decrease over time, that the
equipment will last 60 months and not more or less, and that the
return each month will be the same. And then there's the inestimable
joys of seeing your spouse happy and being able to watch the cricket
in peace.
--
Regards
Norman Harker MVP (Excel)
Sydney, Australia
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