December is generally one of the most expensive months to fly, but it contains a "hidden" window of affordability during the first two weeks. From December 1st to roughly December 12th, fares are often quite low as demand dips between the Thanksgiving and Christmas rushes. However, once schools break for the holidays (typically around December 18th), prices spike dramatically, often doubling or tripling for popular routes. The most expensive days to fly are usually December 22nd, 23rd, and the days immediately following Christmas. If you are looking for a deal in late December, flying on Christmas Day or New Year's Eve can often save you 20-30% compared to the peak dates around them. To get the best rates for a December trip, travel experts in 2026 suggest booking international flights 3–4 months in advance (by August/September) and domestic flights at least 6–8 weeks out, specifically targeting mid-week departures to avoid the heavy weekend "festive" premiums.