​​

The average fare for a flight from the US to Europe will vary by $256 from when a ticket is first offered to the day the plane takes off. A flight from the US to South America will fluctuate in a $262 range over the same period. This is according to Kayak, a travel website, which analyzed millions of searches made by US travelers over the past year.

Kayak found that the cheapest fares from the US to Africa were just 33 days before departure, while the cheapest to Europe were 53 days before departure, and the cheapest to South America were 162 days out. The cheapest flights to Asia were booked 270 days—a full nine months—in advance.

Challenging the conventional wisdom, the most expensive fares typically appear when purchased far in advance of a flight. For example, the average ticket to South America was more than 20% higher than the subsequent cheapest fare when booked more than 300 days before departure.

Only flights to Europe were more expensive when bought on the day of departure instead of 350 days in advance.

In general, the price of flights to all regions jump significantly during the week of departure. Fares from the US to Europe rise by 15% in the seven days before departure. However, even with this big price increase, a ticket to Europe is almost always cheaper than one to Asia or Africa, no matter when you book.

Read This Next: The most valuable keywords to have on a tech resume