The CA mortgage deductible interest cap I believe is 1M.
The problem is that TT is miscalculating by around a 1.5x factor your average mortgage balance, so unless your home is under $666k (where it miscalculated to $1M), you will be losing money on your refund if you refinanced.
For example if your home is worth 1M... your new refi loan balance is correct, but your original loan which has a ~$1M start and $0 end (because it's closed) will be incorrectly averaged as $500k ($1M-$0 / 2) and so it sums that with the new loan to come out with an incorrect balance of $1.5M (amazing) for your $1M home. The result is that you go from having 100% of your mortgage deductible (because it was at the 1M cap), to now only having 67% of it deductible (because it thinks you are over the cap by $500k). You would lose out tens of thousands of dollars of truly deductible interest... for example in this scenario if you had paid $45k in mortgage interest paid in the year, you would be losing out on deducting $15k of it (because it sees only 67% of it as being deductable)... which could translate into a refund loss of somewhere around $3-5k.
