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

https://rivervypa048.huicopper.com/st-pancras-to-gatwick-airport-direct-thameslink-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.