Haven’t booked your Thanksgiving or end of year holiday travel yet? Fear not, procrastinators. According to online booking data, the best days to book are still ahead of us.

The cheapest airfares for Thanksgiving travel will be available between October 29 and November 13, online booking giant Expedia revealed this week, based on historical data analyzed by the company. Booking two weeks to a month in advance of Thanksgiving can save travelers more than 5 percent. But if you wait too long (read, until the week before), you could pay more than 20 percent above the average rate.

For Christmas, the cheapest time to purchase flights will be between November 23 and December 9, Expedia reported. Booking during that window can save travelers around 15 percent. Interestingly, those who wait until the very last minute might get dinged less than early birds.

Last-minute bookers pay about 2 percent more than is typical, while early birds who booked three months or more in advance of their flight paid around 15 percent more than the average holiday traveler, according to Expedia.

For those who are nervous about the prospect of waiting until the end of October or November to book their holiday trips, online travel site Hipmunk offers slightly more conservative guidance. According to the folks at Hipmunk, booking flights for Thanksgiving and Christmas during the first week of September can save travelers an average of 12 percent on Thanksgiving flights and 19 percent on Christmastime flights.

Similar to Expedia, Hipmunk found that Thanksgiving flights will peak around mid-October and then start to dip down again toward Halloween and into early November. They will then rise sharply in the two weeks prior to the holiday, Hipmunk reported. Similarly, Christmastime booking prices see a drop in the two-week window before the holiday and then a sharp increase the week of. 

The online booking sites had additional tips on how to get the best deals when booking holiday travel. According to Expedia, traveling on the holiday itself will often yield the cheapest rates, for those willing to fly day of. Also, avoid starting your trip on the Saturday before the holiday, which is consistently the most expensive day to fly.

Last year, travelers who flew out on Thanksgiving proper paid on average $100 less than those who departed the Saturday prior to the holiday, according to Hipmunk. The site noted that the second cheapest option will be starting your trip on the Monday or Tuesday of Thanksgiving week. The busiest travel day leading up to Thanksgiving is the day before Thanksgiving.

As for around Christmas, Hipmunk revealed that the cheapest day to fly is traditionally Christmas Eve, followed by December 23.

There are a lot of factors that influence the rise and fall of airfares during any given day, week, or month. Expedia advises travelers to set up price alerts for flights, which you can do through booking engines such as Expedia and Google Flights.

Expedia also noted that you are likely to find better savings if you bundle your flight and hotel—whether you book your flight and hotel at the same time or come back and add a hotel later, you can save a few hundred bucks.