Frank Marion noted: >>I want to whip up a quick database, where one of the **fields** has a default >>that is a calculation, or that the calculation is automatically triggered when >>data is entered. >>Balance =Sum(['RentRoll.Due']-['RentRoll.Discount']-['RentRoll.Paid']) Hi Frank, I've not used Access much, but I would suspect it's getting confused because "SUM" is generally an aggregate function working with data from all of the rows (that meet the 'where' clause). It might choke on assigning that to a field in each individual row. Maybe you could distribute an Access 'Report' along with the DB, where the 'Report' thingie does the sums and calculations you want? HTH, RonL.