Gather the information while you are still outside the filing window. Submission is free on the official portal. Once the arrival arrangements are confirmed, check the entry against the flight information you received. Official TDAC portal
What should you prepare before departure?
Have the passport you will actually use, your arrival date, the flight information and the address of your first accommodation. The Immigration FAQ allows group submissions for up to ten travellers. One person can enter the details for a family, after which each traveller should check their name and document number. Thai Immigration TDAC FAQ
A villa address can be harder to find than a hotel. Ask your host for the full address, province and postal code before starting. If you stay one night in Bangkok before travelling to the coast, note both stops and follow the form’s instructions when entering your stay.
What if the aircraft lands on the following day?
Use the new arrival date in Thailand, then bring up the confirmation already issued. The official FAQ identifies four fields that cannot be changed on an existing submission: full name, passport number, nationality and date of birth. A mistake in one of them requires a new submission. Thai Immigration TDAC FAQ
A delay from 11 p.m. to 1 a.m. can move your arrival to the next date in Bangkok. Check the information again if the arrival airport changes, too. Keep the latest confirmation and QR code within reach, including offline. TDAC user guide
Which other travel documents should you check?
Check entry requirements for each traveller through the Thai consular portal. The TDAC and any visa application are separate. Travellers in the same delegation may have different passports and reasons for visiting. Check their circumstances individually before the three-day window opens. Thai e-Visa · Immigration FAQ
The Immigration guide provides an exemption for some connections that do not involve crossing the Thai border. If you need to enter Thailand to change airports or stay overnight at a hotel, confirm how your connection will work. TDAC user guide
When enquiring about a private jet to Bangkok, send the origin, preferred local date, passenger count and first address. Keep passport details for official procedures and the channels used for them.