Assume:

$9,877 = Mortgage interest paid (a loan of $150,000 for 30 years, at 7 percent, using year-five interest)
$1,440 = Property taxes (at 4.0 percent on $180,000 assessed value)
______

$11,317 = Total deduction

Then, multiply your total deduction by your tax rate.

For example, at a 28 percent tax rate: 11,317 x 0.28 = $3,168.76

$3,168.76 = Amount you have lowered your federal income tax (at 28 percent tax rate)

Note: Mortgage interest may not be deductible on loans over $1.1 million. In addition, deductions are decreased when total income reaches a certain level.