The deductible mortgage interest is not limited based on the amount of interest. It is instead limited by the outstanding mortgage principal on all your deductible home loans. For homes purchased prior to December 15, 2017 the limit is $1 million of outstanding mortgage principal and is $750,000 for homes purchased after that date.
If you are not seeing your taxes move much when you enter your interest, it is likely that you were receiving the standard deduction prior to entering the interest. Once your itemized deductions exceed your standard deduction, you start seeing a reduction in taxes but it will not have any effect until then. If you are married filing jointly, your standard deduction is $25,100, so you will not see any benefit from the first $25,100 of itemized deductions you enter.
In addition to mortgage interest, itemized deductions include state and local taxes, gifts to charity, and medical expenses that exceed 7.5% of your gross income.
