You can deduct all mortgage interest that was paid on funds used to buy, build, or improve your home. This is true as long as your mortgage does not exceed $750,000. You can only deduct mortgage interest on the first $750,000.
On the bright side, itemized deductions were limited through tax year 2017 when a taxpayer's AGI exceeded certain limits based on his filing status.
The total amount of the itemized deductions you could claim was reduced by either 3 percent of the amount by which your AGI exceeded the threshold or 80 percent of your total itemized deductions, whichever was less. This is no longer the case. The TCJA has repealed limitations through at least 2025 when the law sunsets or expires unless Congress acts to renew it.