When planning a vacation, the less you spend on flights, the more you can put toward exploring your destination.
The ideal time for domestic flights: 70 days in advance. That's within what CheapAir.com calls the "prime booking window," which stretches from 21 to 121 days early to lock in the best prices. "Fares bounce around but frequently are available for within 5 percent of the lowest price," the study says.
The time of year you're aiming for matters as well. Here's how far out is ideal for each season: