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

https://finneiyp754.bearsfanteamshop.com/how-to-get-to-gatwick-by-taxi-costs-travel-time-and-tips-1

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.