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MEMPHIS, Tenn. — We’ve all probably been in that situation, wondering if you should buy your plane ticket now or wait.

CheapAir.com analyzes millions of fares each year, and here’s what they found about the best and worst times to buy for 2018.

For domestic flights, you’ll get the best price if you book 70 days before takeoff.

Keep in mind though, these are average numbers.

CheapAir found what it calls the prime booking window to be anywhere from three weeks to four months in advance. In general, this is where you’ll find your bargain. Booking too early will get you the best seat selection, but can cost on average $50 more.

On the flip side, booking too late, like within two weeks of departure, can be costly. Procrastinators pay, on average, $200 more for a ticket than those who bought earlier.

There’s also that question of what’s the cheapest day to book flights.

According to this study there isn’t one – at least that made that big of a difference. CheapAir did find Tuesday and Wednesday were the cheapest days to fly while Sunday was the most expensive.