In 2017, the amount you can deduct (called an "exemption") for a dependent on your tax return is $4,050. This amount usually increases each year.
If you have two dependents, you can deduct $4,050 per dependent, for a total deduction of $8,100. If you have three dependents, the total deduction is $12,150, and so on.
There is a limit, though. If you're a high-income taxpayer, your deductions for exemptions may be phased out. This means that at a certain income, you can't take the full deduction of $4,050 per dependent in 2017. At even higher incomes, the deduction amount for your dependents is zero.