The Biblical explanation of the tithe speaks of a tenth of one’s “increase.” We don’t get too nitpicky about all the variables a person can probe like whether an investment nixes or adjusts the percentages or whether an amount has already been tithed upon because of extenuating circumstances. There is no end to that kind of thing if one were trying to get out of paying the tithe. We view the tithe as a starting point on which one is free to add more. It is the willingness of the heart to do what Yahweh expects which is the overriding concern.
Read “The Poor Widows Challenge- A Lesson on Tithing” for in-depth study on this subject.