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

https://martinrdkc501.tearosediner.net/gatwick-airport-public-transport-your-complete-options-guide

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.