Proverbs 3:9 says, “Honour the Lord with thy substance, and the firstfruits of all thine increase.” That means tithes are to be given from the first fruits, from the top, the gross, not the net (Deuteronomy 26).
When you tithe on the income you receive before taxes, you’re acknowledging Jesus as LORD over all your money—even that which goes to the government. That way the money you use to pay taxes with becomes more than just dollars and cents, it becomes blessed seed that you invest in your government.
Tithing off the gross also opens the door for Jesus Himself to help meet your tax needs. Since Gloria and I began tithing that way many years ago, we have never failed to have more than enough to pay our taxes when due.