There is no date yet for 2018 TurboTax to be updated, but you should expect that it will take a while. The software doesn't get updated the instant that a new law is passed. The law that the president signed last Friday makes hundreds of changes. It's not just the PMI deduction. TurboTax has to wait for the IRS to publish procedures and revised forms for all the changes, and then it takes a while to make all the changes in the software, test them, and get IRS approval for the updates. Also, right now the IRS and TurboTax are devoting all available resources to getting ready for filing 2019 tax returns. I'm sure that retroactive changes for 2018 will not be the top priority.
