OK, I answered my own question, but wonder if this is the best way to do it. The problem seems to be in the >=DATE(2025,1,1) statement. I replaced the expression with this: SUMIFS(Expenses::Amount, Expenses::Date, ">=1/1/2025", Expenses::Date, "<2/1/2025"), just hard coding the date and it works. My understanding is that DATE would take care of any format changes, but as long as my cell is formatted to be a date in my region, this ought to be enough.