When is the best time to book international flights?

For US-to-Europe routes, the general sweet spot is booking 2-4 months before departure. Booking too early (6+ months out) rarely gets you the lowest fare since airlines haven't released their cheapest seat tiers yet; booking too late (under 3 weeks) usually means only the most expensive fare classes remain.

Fares also shift with the season: flying in shoulder months (spring and fall) is both cheaper and less crowded than peak summer. If your dates are flexible, comparing a few nearby departure days can sometimes save a meaningful amount, since prices can vary day to day even for the same route.