69 minutes quicker than the National Express coach to Luton (sold from £21.50), for up to £2.50 more. And no booking needed.
Thameslink to Luton Airport, via the Luton DART
ThameslinkLuton DART · Thameslink and Luton DARTPickup, hours & luggage
Boards at. Gatwick Airport station, in the South Terminal; change at Luton Airport Parkway for the Luton DART
Two purchases: £19.10 by contactless at Gatwick (£30.80 between 06:30 and 09:30 and 16:00 and 19:00 on a weekday), plus the £4.90 Luton DART single at its machine or online. A through ticket to "Luton Airport" includes the DART.
Luggage. Racks by the doors and overhead; the DART is built for suitcases.