How to get to Koh Tao
The closest airports to arrive from are in Surat Thani, Chumphon, Nakhon Si Thammarat and Koh Samui with AirAsia, LionAir, NokAir and ThaiSmile. On arrival, you can get the ferry ticket directly to Koh Tao in the airport, you can also check the timetables for the different ferries (Lomprayah, Seatran, Songserm) so you can still take it in the same day.
The alternative to flying is taking the train (overnight sleeper recommended, you can check the timetables and tickets) from Bangkok to Chumphon Southern line or even the bus - you can book your trip here or in any agency in Khaosan Road. For the train it's also possible to get the ticket in Hua Lamphong train station, but it's likely that it's required to do it at least one day before.
Don't hesitate on droping us a message if you have any questions!