Assume that you input daily revenue into the cells B2 through B32 (one cell
for each day).
Enter the formula =sum(B2:B32) in cell B33. That gives you month-to-date
revenue.
Enter the formula =countif(B2:B32,"<0") in cell B34. That gives you the
number of days for which you have recorded revenue.
Enter the formula =B33/B34*31 (number of revenue days in the month). That
gives you projected revenue for the month based on the average daily revenue
month-to-date.
From there, the complexity of you calculations is based on your appetite for
detail.

Tom