Can someone please help me with the calculation of simple payback (breakeven point)?

my formula:
=-1*C8/(0.1*SUM(D8:M8))

info on cells
=-1*Investment /(.1 * sum(10yrscashflowFromInvestment)

I'm afraid to say...
More information needed!

I think What you're saying is:

One cell contains the total Investment.

There is a column containing the amount returned from the investement every unit of time (year?)...

So I don't really follow what you want to find out?
Amount of gain - amount invested?

Georgev, Thanks lot for your attention:

I need to know the answer of simple payback months.

Here is the whole question:

9. Calculate the Simple Payback for the investment in cell D15 (what month will the investment breakeven, excluding cost of money)


Year Investment 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Revenue $100.0 $130.0 $169.0 $219.7 $285.6 $371.3 $482.7 $627.5 $815.7 $1,060.4
Expense 50.0 51.5 53.0 54.6 56.3 58.0 59.7 61.5 63.3 65.2
Cash Flow -$300.0 $50.0 $78.5 $116.0 $165.1 $229.3 $313.3 $423.0 $566.0 $752.4 $995.2
Margin % 50.0% 60.4% 68.6% 75.1% 80.3% 84.4% 87.6% 90.2% 92.2% 93.8%
Growth 57.0% 47.7% 42.4% 38.9% 36.6% 35.0% 33.8% 32.9% 32.3%


Cash Flow CAGR 47.5%
IRR 47.6% $0.81
Simple Payback (months)

Is this for an Excel Class or some type of finance/accounting class?