When can you include rental expense in 2018 if check is written in Jan 2019?

[Carl]

You can't include it as a 2018 expense, since you didn't pay it in 2018 (whatever "it" is).

[SweetieJean]

You are asking from TT Live, for which you are paying extra:

https://ttlc.intuit.com/questions/4124827-how-do-i-connect-with-a-tax-expert-in-turbotax-live

[Carl]

It really doesn't matter. If you didn't pay the expense in 2018, then you can't legally claim it as a 2018 expense on your 2018 tax return.