data projections limited by IF formula using dates

[indigost]

Hello.

Column A lists annual bills to be paid (insurance, room hire, fees etc). Row 1 contains dates by fortnight, while following rows contain amounts to be paid into a holding account each fortnight for each bill (ie row 2: annual amount of bill1/26). Each bill has a different due date but the date is fixed annually (bill1 is always 18 jan, bill2 is always 15 april etc). For each bill, the fortnightly payment is the same through the billing year, and bills are forecasted to rise 10% pa. A linked worksheet includes the annual billing amounts as well as the fortnightly amounts (pa amt/26) (a column for each year's pa amount and a column for each year's per fortnight amount).

In any one fortnight, some bills are in 2010 (those with due dates later than the Row 1fortnight date) and some bills are in 2011 (those with due dates already past).

I use the following formula:
=IF(fortnight date < 2010 due date, 2010 data, 2011 data)


This works well but now I'm stuck because I want to project the data forward to 2012 and beyond, but my if formula only lets me use "if not 2010 then 2011". I tried taking the year off the due date but then it didn't work at all. I also tried deleting 2010 data (moving 2011 data over to column e in formula above), but this resulted in errors.

I'd love a formula that read "if earlier than x date 2011, use 2010 data, if later than x date 2010 but earlier than 2011, use 2011 data, if later than x date 2011 but earlier than x date 2012 use 2012 data" etc Is this possible?? Or any work around? thanks for any help.

Hope the explanation of the spreadsheet is clear - I can't post it because of confidentiality and trying to create a mini version resulted in way too many errors to be useful.