We moved out of a home during the time that we owned it (rented it out), moved back in, refinanced, then sold in 2018, which settlement docs do I use for the cost basis?

[toddfern]

Your basis is your basis, i.e., the purchase price when you bought the property before you rented it.  Refinancing and rentals don't change the basis.  Those transactions may, however, change the mortgage interest you can take, and can convert money you took in as rent to income.  Money you spent on the house may also count as a business expense.