It’s no secret that airfares fluctuate a lot. To play safe, you should always book cheap international airfare on Tuesdays, and that too early in the morning. You will also find many airlines launching sales late Monday night, forcing other airlines to drop their rates to come back into the reckoning. As a rule, Tuesdays, Wednesdays, and Saturdays are the least popular days to fly, so tickets are often less expensive. On the other hand, Fridays and Sundays are the most desirable days, so obviously they will be expensive.