Planning to take a much-needed vacation this summer? Fly out on a Tuesday and you'll save a chunk of cash.

Passengers who schedule flights that depart on summer Tuesdays will pay an average of $77, or 17%, less for a ticket than they would if they fly out on a Sunday, the most expensive day of the week to fly, according to a survey by Cheapair.com.

The booking site compared fares for 900,000 round-trip flights scheduled between June and September and found that the average fare for a Tuesday was $367. That compares with $444 on Sundays, $412 on Fridays and $402 on Saturdays. Wednesdays were also cheap at an average of $368.

It's also much better to book in advance. The scheduling sweet spot is a window of one to three months before your trip, with booking 54 days in advance yielding the lowest prices, Cheapair found.

Related: For sale: Dream beach homes

Currently, late August airfares are an average of $100 lower than those for July.

Jeff Klee, Cheapair's CEO, said the company's survey also busted a couple of myths. One was that booking just before your scheduled trip could save you a lot of money.

"That's left over from the years when airlines were less healthy," said Klee. "They would often find themselves with lots of empty seats and would have fire sales to fill them."

Related: 10 vacation experiences of a lifetime

Now that so many airlines have merged, airplanes are running at or close to capacity most of the time.

"You just don't see a slashing of fares anymore," said Klee.

Another thing Cheapair found was that it no longer pays to buy your ticket on a certain day of the week. Average fares were within a dollar of one another no matter which day a person booked.