Summer is fast approaching. And with it, the promise of another Fourth of July holiday and (if you’re traveling) another expensive plane ticket. In case you haven’t noticed in the past, July 4th is without a doubt one of the busiest travel holidays of the year – if not the busiest.

And the worst part is – we’re busy as well. Too busy to plan all of our travel ahead of time . Fortunately, that’s where the travel website, Hipmunk, comes in. Hipmunk evaluated “historical data” and discovered the best time to buy your July 4th airplane ticket, according to the Huffington Post.

According to their findings, “the best time to book your July 4th flights is during the week of Memorial Day.” That means there’s still time (plenty of time) left to book those tickets. The site also found that “those who book their flights between May 26 and June 1 could save $150 by not waiting until a later date.”

The Huffington Post also pointed out that those who booked during the Memorial Day holiday only spent about $417 on airplane tickets. But “those who booked three weeks later spent an average of $547.”

In other words, it’s worth it to book your airplane ticket early. Check out this helpful chart below to save on your vacation airfare this summer.

[h/t Huffington Post]