formula - each month add $ amt to total

[SDKBRK]

I have a spreadsheet in cell A1 is 7/1/07(as text), cell B1 is $1200.
In cell C1 is =B1 and I need the formula to increase the $amt to $2,400 when its more than 30 days from the date in cell A1, and increase the $amt to $3600 if its more than 90 days from cell A1.

Thanks,
Di

 

[Dan Waterloo]

C1:

= B1 + if(today() - A1 > 30, 1200, 0) + if(today() - A1 > 90, 1200, 0)