We bought a new home on 12/18/18; loan = $784K. Sold our old home (avg mortgage bal was $514K in 2018) on 2/25/19. How do I compute the avg mortgage bal for the new home?

Turbo Tax Premier just sends you to IRS Publication 936, but that document doesn't give guidance on partial-year mortgages. I would imagine that a weighted average is needed, but there are numerous ways to calculate that (based on daily balance, or monthly balance, to name a couple).

Both homes were our primary residence, the mortgages just happened to overlap for a couple of months until we sold the first home. Please help! I will have the same problem next year, but with the first mortgage (since we had that one for only two months in 2019).