Calculation of monthly payments per employee

[Deborah]

I am looking for a formula that gives me the amount to be paid at the end of
each month per employee knowing that:

- If the month starts on 16th or ends on 15th, half the allowance should be
paid (1/2)
- The first month, the travel costs inbound have to be added to the allowance
- Travel costs outbound should be paid in the month that is inserted in
column J
- Contracts can be extended (the end dates are inserted in columns C, D, E)
the calculation should also include these dates if there are any

Column A: Start date contract (16/03/2010)
Column B: End date contract (30/06/2010)
Column C: End date extension 1 (15/09/2010)
Column D: End date extension 2 (empty)
Column E: End date extension 3 (empty)
Column F: Monthly allowance (600€)
Column G: Travel cost inbound (500€)
Column H: Travel cost outbound (450€)
Column I: Month payment outbound travel (October 2010)

SOLUTION
Column J: March 2010 (800€)
Column K: April 2010 (600€)
Column L: May 2010 (600€)
Column M: June 2010 (600€)
Column N: July 2010 (600€)
Column O: August 2010 (600€)
Column P: September 2010 (300€)
Column Q: October 2010 (450€)

I hope someone can help.

Thank you,

Deborah