What are the chances of being denied re-entry to Thailand with a history of long stays and short trips?

@John *******

They absolutely do calculate dates. Entry history is electronic and visible instantly, there is no reliance on “calendar years” or on explanations at the counter. Immigration looks at your total time spent in Thailand within a rolling period and whether your pattern still fits ordinary tourism. Being polite always helps, but it does not override entry history or discretion exercised on that basis.

@Michael *******

as said…

@Jan *****************

where is this total time in Thailand within a rolling cycle listed?

@Dennis ********

It isn’t listed anywhere as a fixed rule. There is no published regulation that defines a specific number of days allowed within a rolling cycle. This is simply how Thai Immigration has applied discretion in practice for many years. When assessing entry, the IO looks at your overall travel pattern, including how long you have spent in Thailand over time, how frequently you enter, and whether your stays resemble genuine tourism or de facto long term residence without the appropriate visa. The concept of total time spent within a rolling cycle comes from observed practice and case handling, not from a written statute or formal limit.

If you prefer simpler wording, it is generally the case that if you maximise two visa exemptions within a period and spend around 180 days in Thailand without a visa, your third entry attempt becomes a gamble and can just as easily go wrong as go through without issues.