Mormon scripture states that members should be tithed, that they “shall pay one-tenth of all their interest annually” to the church. In order for members to qualify as worthy of god’s stamp of approval, i.e., to receive a recommend to enter a Mormon temple, they must indicate in a private interview with their ecclesiastical leaders that they pay “a full tithe.”
But what is a full tithe? Unfortunately, the church doesn’t give very much more clarification than what is stated in the scriptures. The word “interest” has been defined to mean “income,” but beyond that, the members are left to themselves to determine exactly how to calculate what counts as income and what doesn’t. It’s hard to blame the church authorities for not wanting to create a tome equivalent to the US tax code to clarify the tithing code. For one thing, it would encourage pharisaic dedication along with its attendant loopholes. But perhaps even more convincingly, by making a statement that determining the amount to be paid as tithing by each member is a decision to be arrived at by the member in consultation with god, my guess is that the amount donated is, on average, higher than it would be if they published a set of guidelines.