In most cases, this will be the amount in box 1 on Form 1098, Mortgage Interest Statement, or on a similar statement you received from your mortgage holder.
To enter your Mortgage Credit Certificate in TurboTax is a 2 step process. Enter the mortgage interest then enter the Mortgage Interest Credit Certificate.
Step 1 Enter the Mortgage Interest
Select the Federal Taxes tab
Select Deductions and Credits
Select I’ll choose what I work on button
Scroll down to Your Home section and
Select Mortgage Interest
Enter Mortgage Lender and continue through the screens answering the mortgage interest questions.
When you return to the Home Loan Deduction Summary you will have the option to add additional loans if needed, with the blue Add Another Lender button. Enter all mortgage interest.
Done
Step 2 Enter the Mortgage Credit Certificate
In Federal, Deductions and Credits
Scroll down to the Your Home section
Select Mortgage Interest Credit Certificate start/ update
Answer Yes to “Do You Have a Mortgage Credit Certificate”
Continue to the “Enter Mortgage Interest Credit Info” screen
Enter the information from your certificate. For the mortgage interest field, only enter mortgage interest that was for the loan covered by your certificate (do not use interest from other loans) and press Continue
If you have a carryover of this credit from previous years, answer Yes on the “Mortgage Credit Carryover” screen, then enter your carryover information from the last three years
If you itemize your deductions on Schedule A, you must reduce the amount of home mortgage interest you would otherwise deduct on Schedule A by the amount on Form 8396 - TurboTax will deduct the proper amount for you.
See About Form 8396, Mortgage Interest Credit | IRS for more.