I'm trying to write an Excel function that will help me find the earliest
possible date that I could deliver a product based on my current delivery
schedule and a user-entered order date. The hope is that I'd type an order
date in one cell and have Excel identify the earliest possible delivery date
in another.

I have a list of currently scheduled deliveries in column G and in column H
the number of days between a currently scheduled delivery and the next
subsequent delivery as shown below.

G H
Delivery Dates Days Between Deliveries
1/5/2010 45
2/20/2010 33

My criteria a

1) I need a certain # of days between current deliveries in order to squeeze
an additional delivery in (i.e. if I can deliver every 20 days I need a 40
day gap)
2) The date Excel identifies must be long enough after the inputted order
date to meet my supplier lead times.

I'm trying to write a function that will first look down the list of
delivery gaps in column H and have it pick the first gap that is sufficiently
large for me to squeeze an extra delivery into and then look at the date next
to the identified cell in column G to verify that it is far enough from the
order date to meet my lead times. A coworker and I have exhausted our
knowledge as well as anything we've found online and are still stumped. Any
suggestions would be very much appreciated.