The Bureau of Transportation Statistics tracks average domestic airfare quarterly; in Q3 2023, the average US domestic round trip cost $388, up from $280 in 2020 but still below the inflation-adjusted 2014 peak of $420. International airfares are harder to average, but the tools for finding anomalous low prices have matured substantially since 2015 — and the gap between a traveler who uses them and one who books directly through airline sites has widened.

Error Fares and Mistake Fares: Going (Formerly Scott's Cheap Flights)

Going (going.com) monitors airline pricing systems for fares that fall significantly below normal — either genuine error fares (pricing mistakes) or sales not widely advertised. The free tier provides alerts with a 1–3 day delay; the Premium tier ($49/year) delivers alerts in real time, which matters because mistake fares are corrected within hours. The service launched as Scott's Cheap Flights in 2015; the rebrand to Going happened in 2022.

A realistic expectation for a Going subscriber: 4–8 genuinely useful fare alerts per year for a typical US departure city, of which 1–2 will be actionable based on dates and destinations. Premium members in major hub cities (New York, Chicago, Los Angeles, Miami) see more alerts than those departing secondary markets. Notable historical alerts have included round trips from the US East Coast to Europe for $350–$400 (normal price $700–$900) and transpacific fares to Southeast Asia for $500 (normal $900–$1,200). Airlines occasionally honor error fares and occasionally cancel bookings; the Department of Transportation does not currently require enforcement of mistaken prices.

Google Flights: The Baseline Tool

Google Flights (flights.google.com) is the most useful free tool for flexible-date fare searching. The "Explore" map view shows fares from your departure city to all destinations on a world map, updated in near-real-time. The "Price Graph" for a specific route shows 2-month fare trends. The "Cheapest Month" view identifies the lowest-cost month to fly a given route.

Key technique: search with "Flexible Dates" (+/- 3 days) for routes where scheduling flexibility exists. On a New York–London search, the price difference between the cheapest day in a given month and the most expensive can easily be $200–$400 on the same airline. Google Flights also tracks prices and sends email alerts when prices change — set this for routes you're considering and check back in 2–4 weeks before booking.

Hopper: Predictive Pricing

Hopper's core claim is a price prediction algorithm with approximately 95% accuracy (per the company's own published accuracy figures). The app analyzes historical fare data and advises whether to "buy now" or "wait." In practice, the "watch" function is most valuable: add a trip to the watch list and Hopper notifies you when the price hits a threshold it predicts is near the local minimum. The app also sells "price freeze" options ($10–$30 to lock a fare for 14 days) that can be worth the fee on volatile routes.

Hopper's model has expanded to include hotel and car rental pricing with similar predictive framing. The primary criticism is that the algorithm performs better on domestic routes with rich historical data than on newer international routes or low-cost carriers that change pricing less predictably.

Budget Breakdown: A Real Example

A week in Lisbon from New York, booked 6 weeks in advance with TAP Air Portugal during shoulder season (May):

  • Round-trip airfare: $620 (booked via Google Flights alert, TAP Economy)
  • Accommodation: Home Lisbon Hostel (dorm) $28/night x 7 = $196; or Casa do Principe guesthouse $85/night x 7 = $595
  • Local transport: 7-day Viva Viagem card (unlimited metro/bus/tram) $18
  • Food: Lunch at tascas (neighborhood restaurants) averaging €9–€12/meal; dinner €15–€22 at mid-level restaurants
  • Total budget traveler (hostel): approximately $1,200–$1,400 for 7 days including airfare
  • Total mid-range (guesthouse): approximately $1,600–$1,900 for 7 days including airfare

By comparison, BTS data shows the average American spends $1,300 on a domestic round trip plus accommodation per person for a 5-night trip — meaning Lisbon in shoulder season is cost-competitive with a domestic US trip.

Booking Windows and Timing

Skyscanner publishes booking window data annually. For transatlantic flights, the average sweet spot for lowest prices is 1–3 months before departure, with prices typically lowest on Tuesdays and Wednesdays. For Asia, 2–4 months ahead. For peak holiday periods (Christmas, Thanksgiving), the low-price window opens 5–6 months out. Booking on the day of travel produces fares 20–40% above the route average in most markets. The "avoid Monday morning" rule for transatlantic booking (when business travelers reset weekly schedules and demand spikes) has degraded as pricing algorithms become more real-time, but Tuesday–Thursday booking still shows slightly lower average prices in Skyscanner data.

Sources & Further Reading