Distribute specific amount to months

Hello everyone
I have specific amount (200) and I need UDF function that enables me to distribute this amount according to the following
For example:
If start date is 25 / 3 / 2016 (March) & End date is 3 / 7 / 2016 ( July)

So the number of days in March is 7 and the number of days in July is 3
and other months [April - May - June] are full days

Now I calculated the expected for the first month (March) with this formula

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and for the last month (July) with this formula

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As for the rest of full months : (200 - sum(the first month , the last month)) / the number of full months

Can it be done using UDF function which refers to Start date & End Date & The amount (Cost)
These are the three parameters

Hope it is clear
Thanks advanced for help

if your dates inclusive? or exclusive of start and finish?

also may has 31 days...your example shows 30

see my attempt of UDF
note i changed the headers to be actual dates in order to recognise months
i added additional UDF endofmonth to mimic EOMONTH in VBA
which i took from
http://answers.microsoft.com/en-us/o...2-0594c350ade2

Thank you very much for this great solution
But it depends on the number of days I think and this caused incorrect results ( not as expected)
Just we depend on the number of days for the start and end dates only
but the rest of month in between would be distributed equally (as in example there are three months in between so the rest of the cost (200 - (14 + 6)) = 180 and 180 / 3 = 60

Another point i don't need the fourth parameter .. the formula of UDF would be put in twelve cells (months of the year) so no need for this parameter (I hope it can be hard-coded instead)
Hope this make any sense for you
Best regards

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i have replicated your outputs based on your information

the fourth parameter is the anchor point
it needs to know where in the 12 cells to start ....

Thanks a lot for this wonderful solution
You are great

Just one point as for the fourth parameter .. Can you skip it and depend on the months numbers (1 for January, 2 for February ... as I am afraid of regional settings to affect the UDF ..) so I think numbers will not affect it
Thank you very much

it would require a little of rework but yes you could use 1,2,3,etc
the issue is because it is a UDF people can put the wrong month in the wrong cell

if it was a simple macro then you can of course just hard code the cell itself

i am not sure how to extract the address for UDF based on where the formula is placed..... i am not sure if it is possible
will do some research

Thanks a lot for reply
If it is possible to be done by macro not UDF , It is ok ..do it using subroutine not UDF

@Mr. Karedog
Thank you very very much for this wonderful and fascinating solution and analysis ..Now I have the choice between both of them
Best and kind regards