Booking airline round trip without knowing return date?

I have a relative who plans to fly from NJ to CA and stay for an as yet undetermined number of months. Can he buy a round-trip ticket without providing an exact return date? If not, won't the cost of two one-way tickets be much more expensive? Would he be better off buying the round-trip and then paying to change the return date (assuming that can be done)?

Depends on the airline/timing. I've often purchased one way fares and it turns out to be the same (or less, if you book far enough in advance). JetBlue in particular prices all fares as one-ways.

One ways to CA are usually half of a round trip. In this case it makes no sense to buy a return ticket.

I've found one-ways to be about half recently as well. Plus it gives you the flexibility to look at other airlines for times.

If you buy a round-trip ticket, the typical airline will charge a change fee plus any difference in the airfare.
Check the rules for changing flights first.

If Southwest goes to wherever you are flying, I recommend them as their fares are not different for one-way vs round-trip. Also, they do not charge change fees (just fare difference) if you make a reservation and then change it later. So, for situations like yours, they are a great choice.

Remember also that if you're booking one way trips, you're not stuck with a single carrier. You can fly whoever has the best fare at the time of booking.

Almost all airlines now have "segment" option. When I book E-W coast, there is never a difference for booking together or separately. Go with the one-way.

Change fees are now $150 plus cost of difference.

Thanks, all, for the useful information.

In the "old days", the one way was cost prohibitive. Today, it's more often just about 1/2 the cost of the ticket. This is for most airlines. The only one I have found to be poor with this has been AA-often seems higher to do one-ways.

I think it's called an open ended ticket.

"Unlike a regular return ticket, an open-ended airline ticket sends you to a destination on a specific date, with a flexible return date -- usually within one year of your departure date. Although the ticket may be more expensive than a set return or one-way ticket, not all airlines offer open-ended tickets, so you should ask to speak to a customer service representative about this option."

+1 for Southwest. Can't beat them for flexibility and transparent pricing.

Related question: Is there an optimal time to buy that California ticket fare-wise? I know that last-minute purchases are very expensive, but how far in advance is wise? A month? Two months?

Exactly 21 days in advance, according to a HuffPo article.

I've also heard Tuesday.

Some booking sites will show you the price depending on the day you fly. That should also give you an idea of the best time to buy.

Thanks!

Also check Jet Blue.