For my specific itinerary with United Airlines, one-way flight from A->B is 900$, and a return flight A->B->A is 1350$. They are offering free changes right now https://www.united.com/ual/en/us/fly/travel/notices.html#ChangeFeeTerms
I am pretty sure I will need to change the return leg because I don't have fixed plans for the return yet.
My question is - How is the price for new ticket calculated if changing only the return leg of a flight? Should I a return flight since it's cheaper (for a 2-way flight) or book only 1-way because the difference in airfare when rescheduling the return leg could be substantial?