I have a budget spreadsheet with future pay dates for the next number
of years in row 1 (H1..BA1) across the top.

Down the left in col B (B2..B800) I have "Due Dates",and in col C
"Amount"

I have the formular =IF(AND($B2=H$1,$B2<I$1),$C2,"-") copied to about
150,000 cells that calculates when an amount is due, and puts that
amount under the appropriate pay date.

By inserting this formular, the spreadsheet had blown out quickly from
700Kb to 3.8Mb.

Can the above calculation be achieved with a macro that would update
those 150,000 cells (H1..BA1000) with the click of a button?

Regards, Kaye