Calculating contribution of sales by month with given amount, start date, and end date

Hi all, I am a little hung up on the following: I have a column with sales numbers and two more with a start date and end date.
I am trying to figure out the monthly contribution of each sales amount. For example, if there is $100,000 in sales with a start date of 10/1/12 and end date of 11/30/12 there will be a total of 61 days (31 in oct. and 30 in nov.) and $50,820 and $49,180 recognized in each month. I also need to think about partial contribution if the start/end date is after the first of the month. The sales will immediately contribute on the start date and extend through the end date.
Ultimately, I would like to have a column with several total sales numbers, months extending across the spreadsheet with total sales amounts being allocated according to their contribution.
I attached the file (I had a max/min formula I used in the past for something similar but it's not working in this sheet)Example.xlsx.

Thank you!

Hi,

Probably a slightly easier way to do this however my solution still works.....

You need to do the following on your spreadsheet...

1. Insert a column to the left of column E so that your Jan Column is now in column F.
2. Add in new date to column E cell E2 being 31/12/2012
3. Change your cell at F1 to be Jan-12, then hover over the bottom right of the cell to get the + sign and drag right to fill right - this will fill the first day of each month in each cell right.
4. enter the following forumla into cell F3 and then drag it down and right to fill the table

=IF(AND($C3<F$2,$C3>E$2),(F$2-$C3+1)/($D3-$C3+1)*$B3,IF(AND($C3<F$1,$D3>F$2),(F$2-F$1+1)/($D3-$C3+1)*$B3,IF(AND($D3<G$1,$D3>E$2),($D3-F$1+1)/($D3-$C3+1)*$B3,0)))

You are done!

Hope that helps - let me know if you need any more assistance..

Cheers

This works perfectly! Thanks so much for the Help!!!