If this question is “Why should I pay tithing when the stock market is down”—meaning when times are economically tough—we would quote President Kimball:
“The poor have special need to tithe. There are people who say they cannot afford to pay tithing, because their incomes are small. They are the people who need the blessings of the Lord! No one is ever too poor to pay tithing, and the Lord has promised that he will open the windows of heaven when we are obedient to his law. He can give us better salaries, he can give us more judgment in the spending of our money. He can give us better health, he can give us greater understanding so that we can get better positions. He can help us so that we can do the things we want to do. However, if we like luxuries or even necessities more than we like obedience, we will miss the blessings which he would like to give us” (Spencer W. Kimball, The Teachings of Spencer W. Kimball, , 212).
If, however, this question is simply “Should I pay tithing if the market is down and I am losing money?” we would teach the following: Tithing is defined in the scriptures as “one-tenth of all their interest annually” (D&C 119:4). President Faust explained that verse this way:
“The law of tithing is simple: we pay one-tenth of our individual increase annually. Increase has been interpreted by the First Presidency to mean income. What amounts to 10 percent of our individual income is between each of us and our Maker. There are no legalistic rules” (James E. Faust, “Opening the Windows of Heaven,” Ensign, Nov. 1998, 59).