When I arrived in Bangkok on the 21st January 2015, my passport (UK) was stamped "Admitted until 19th February 2015". I am not clear whether I have to leave Thailand on the 19th February, or can stay on the night of the 19th and fly out on the 20th February. Can anyone help clarify this? I was hoping that I get a 30 day stay on a tourist visa, and already have a flight booked on the 20th February. It will cost about 5000THB to change my air ticket. I think the stamp might be better if it stated "To depart Thailand not latter than 19th February".

You should leave on the 19th. The arithmetic is correct as parts of a day count as a day. However for 1900 Baht you can extend that permission to stay at an immigration office.

Edited January 26, 201511 yr by Briggsy

If leaving by air in BKK no overstay fine will be levied for 1 day overstay only. There will be a notation made in your passport that you

overstayed, but it will not prevent you getting a new visa and returning.

I was hoping that I get a 30 day stay on a tourist visa, and already have a flight booked on the 20th February.

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You count 30 days that you are in Thailand not 30 x 24 hours. You were in Thailand on Wednesday 21st Jan, no matter what time you arrived. That was day one, not day zero.

And you're not here on a Tourist Visa, but a visa exempt entry. If you want to be super safe, during the week before your permission to stay expires, go to an immigration office and apply for a 30 day extension of that permission to stay. If I counted right, that would extend your stay to 21 March. Costs 1900 baht.

Or just carry on as planned and leave on the 20th February. For one day, they'll let you slide when you depart from the airport.

Edited January 26, 201511 yr by Suradit69

Thank you all for taking the time to reply. My silly mistake for realising that January has 31 days.

JUST to be safe, I will bite the bullet and pay my airline 5000 Bt to change departure to 19th February. I have heard of horrific delays due to long queues at the immigration offices. ladamani. END OF DISCUSSION ON THIS TOPIC

is that your final word, admitted to 19th means just that, not the next day. an expensive maths lesson. but as others have said no problem with going on the 20th.