On my 1098 there is no Mortgage origination date. What should i do?

The lender should have entered the date for you, however you can obtain the date in a couple of ways. You can enter a date as close to the origination of the loan as you can find, or contact your lender for the specific date, and/or your documents you received at the time of the loan.

As noted in the information shown by clicking on the '?' beside the Mortgage origination date (Box 3):

We need your mortgage origination date for a couple of reasons:

• If you took out your loan before 2007, then you can’t deduct any mortgage insurance premiums you paid.
• To figure out your deduction if you’re amortizing your points (that is, spreading your points across the life of your loan). To get this right, we need the date to be accurate.
• Depending on your loan balance and what you've used the loan for, we'll help you figure out how much interest you can deduct.