Section 86.31 - How does the Service know how much money will be available for BIG grants each year?(a) We estimate funds available for BIG grants each year based on the revenue projected for the Trust Fund. We include this estimate when we issue a NOFO at http://www.grants.gov.(b) We calculate the actual amount of funds available for BIG grants based on tax collections, any funds carried over from previous fiscal years, and available unobligated BIG funds.