not a good one but you could try following:
A1: Total Amount
A2: Installment
A3: First Payment (first Friday you put)
A4: Today date() (or use NOW())

Formula in A4 (Left Amount)
=IF((A1 - INT((A4-A3) / 14) * A2) < 0, 0, (A1 - INT((A4-A3) / 14) * A2))


"jdmagoo" wrote:

Hi all, basically what im trying to create is a spreadsheet showing how many
payments i have left on an item i purchased. Now i pay $100 on this item on
every 2nd friday. So my question is, what is a formula that will look at
todays date and reconise that it is the second friday when payment is due and
reduce a given figure in a cell by $100. For example, Total cost is $1000,
payments = $100, payments are due on 07/10/05, 21/10/05, 04/11/05 etc So when
the 07/10/05 arrives total cost will = $900, when 21/10/05 arrives total cost
will = 800 etc. Obviously when the date is other than specified the total
cost dosnt change.

Hopefully i have made my self clear and somebody can help out with ths dilema

Many thanks
James