Maaser Deductibles

Question

Are there any expenses that one is allowed to "deduct" from his income before calculating the amount of Maaser one must give?

For example, if one makes a hundred thousand dollars a year, but his living expenses, food, taxes and school tuition take up ninety percent of his income, must he pay ten thousand dollars for Maaser or one thousand?

Answer 1

Dayan Raskin says that the following are deductibles:

1. Any overheads that one must pay to earn one's money. For example, if one earned $100,000 but must pay rent, workers, wholesaler, insurance, etc., he doesn't really earn the full $100,000. Therefore, he can pay less Maaser.
2. Taxes. If one earned $100,000 dollars, but pays $10,000 in taxes, he doesn't really earn $100,000 but $90,000.
3. Transportation costs. If it takes $5,000 dollars to get to work, he doesn't really earn $100,000 but $95,000.
4. Cost of childcare to supervise children during working hours. If it costs $5,000 for a babysitter, he doesn't really earn $100,000 but $95,000.

Mortgage is not deductible.

Though if one can't afford to give Tzedaka (meaning, if he was to give Tzedaka he would so poor he would be elegible for Tzedaka himself), he can make a "buddy system" with another such individual with which they can exchange Maaser.

Answer 2

Although not commonly practiced (that I know of), it is worthwhile to mention the approach of the Chofetz Chaim in Ahavas Chesed (2:18:3) is to deduct all non-discretionary household expenses and to give maaser on the net income.

I don't know if non-discretionary expenses only includes basic necessities, or would also include expenses which are culturally accepted (telephone, insurance, etc.)