From Croydon, hop on Southern or Thameslink from East Croydon station

https://rylanfdkl454.theglensecret.com/brighton-to-gatwick-airport-train-times-fares-and-tips-2

From Croydon, hop on Southern or Thameslink from East Croydon station. Trains to Gatwick are frequent and fast, often taking less than 20 minutes platform to platform.