There have been lots of arguments about whether people should tithe on their gross income or their net income. I think it is best to let the individual decide, but after doing a lot of research, I have decided to tithe on the net income.
1) It is more affordable and possible to do even if a person is in a high tax bracket. But gross tithing is not practical or even possible if a person is in a high tax bracket. Middle-class Americans might be able to tithe on their gross, but what about the European who is taxed at a much higher rate? What about the person who lives in a country where he might be taxed as high as 90% of his income? What about the person who earns a gross pay of $50,000 but is taxed half of his income and has a net pay of only $25,000? In a case like that, giving 10% of gross pay would be equivalent to giving 20% of your net pay! That's way too cost prohibited. Gross tithing is not practical or possible in these cases, but net tithing is always possible regardless of how much a person is taxed.
2) There is at least some evidence in the Bible of net tithing on crops. For example, the farmer would tithe on what he harvested from his crop, not the entire field. He didn't include the crops that were left in the field, or the ones that got spoiled, eaten by insects or wild animals, or damaged by bad weather.
3) While most Christians believe that they should tithe, many do not tithe in actual practice. Many people would be willing to tithe on a regular basis if the tithing amount is reasonable and not cost prohibited. Net tithing qualifies in that category. A lot of church leaders advocate gross tithing because they think that they are getting more money. However, they are actually getting less money that they would have gotten. If church leaders insist that gross tithing is the only acceptable way to tithe and that net tithing is not good enough, then people will give up on tithing altogether and not bother to tithe at all; especially if they find gross tithing too cost prohibited.
Whether you agree or disagree with me, I encourage you to respond and tell me what you think. (Please do not write if you believe that tithing is not for Christians. That is a different topic and I won't allow it to be posted here).