This is how much you can expect to save by booking a Hacker Fare, based on how many weeks in advance you book your trip.
From United States
You should book a flight when...
For the most part, it looks like you can save the most by booking a Hacker Fare the closer you are to your travel dates. So, if you don't have a lot of time to plan, combining 2 one-way tickets will help you cut costs when compared to finding a round-trip fare. But as we always say, if you see a good deal -- book it.