How to Buy an Open Ended Airline Ticket
Once upon a time, you could buy an open-ended round trip airline ticket, with a set departure date but no set return; in effect, you were paying ahead of time to reserve a seat for whenever you decided you wanted to come back. Nowadays, most airlines don't offer this option – but you can get something similar if you're willing to pay to fly on a flexible or refundable fare.
Enter the Flexible Fare
Most airlines will happily sell you the same seat, whether it's in coach class or first-class/business class, at multiple price points. Each different fare class comes with its own set of perks. Buy the cheapest seat, and you'll have to pay hefty change fees for rebooking your flight. Buy the same seat at the full fare or highest price point, and you might earn extra frequent flier miles, be in line for free upgrades, skip change fees entirely, or even get your money refunded if you change your mind about traveling.
So while you do have to choose a return date when you book that pricey full fare ticket, you can just rebook it if your plans change. Look for key words like "flexible," "unrestricted" or "fully refundable" as clues that you're looking at a ticket that can be easily changed. Make sure to read the fine print, because each carrier's terminology differs somewhat, and some of them are very good at still sneaking in hidden rebooking fees or limiting the time period in which you can rebook your flight.
Often, corporations that require a lot of travel will strike a deal with airlines for discounted flexible fares. Unless you're the one writing the corporate checks, this works out to a flexible, open-ended fare for you without any of the accompanying pain in your wallet.
The Gift Card Workaround
If you want to gift an open-ended ticket to someone else, try this clever workaround: Buy them a one-way fare for the outbound trip; then give them gift cards for booking a return flight at their convenience. Some airlines sell gift cards or gift certificates directly, while others will accept prepaid gift cards with the Visa or Mastercard logo. Obviously, this works best if they'll book the return trip early enough to get an inexpensive seat; otherwise, they might end up paying full fare prices anyway. This also puts the other person in control of – and makes them accountable for – any extra fees they incur on the return trip, such as checking a bag if their souvenirs wouldn't fit in a carry-on.
Here's another idea if you or whoever you're buying the ticket for will be booking the return date well in advance: If you're on a tight budget and a cheap seat plus the airline's change fee cost significantly less than a full-fare flexible ticket, it might be worth taking the calculated risk of buying a cheap seat and rebooking it later if need be.
Special Options for Students and Teachers
The last bastion of the open-ended fare structure is a multi-destination travel pass, such as through a travel club like STA Travel, which caters to students and teachers. If you qualify, you could get a great deal on flexible passes to travel around the world or internationally – but as always, pay close attention to the restrictions in the fine print. You may be allowed only a certain number of fare changes, or you may need to redeem them within a set period of time; and if you end up in a more expensive seat than the one you originally booked, you'll usually pay the difference in price.