Section 42 — Calculation of detention period
English translation
In calculating the period of detention, it shall be counted from the date of the court's judgment. If there is a term of imprisonment to be served before detention, the imprisonment shall be served first, and detention shall begin from the day following the day of release from imprisonment.
The provisions of Section 21 shall apply mutatis mutandis.
This English translation is provided for reference only and has not yet been firm-verified — always rely on the Thai original.
Firm annotation
Section 42 governs the timing of a detention order made under Section 41. As a rule the period runs from the date of judgment, but where the offender also has a prison term to serve, imprisonment comes first and detention starts the day after release, so the two do not overlap. The section borrows the time-counting method of Section 21 (the rule for computing terms of confinement) by analogy. It completes the habitual-offender scheme of Sections 40 and 41 by fixing when the three-to-ten-year detention period begins and how it is measured.
Why this matters in practice
For anyone facing both imprisonment and detention, the practical point is sequence: you serve the prison term first, and the three-to-ten-year detention only begins the day after you are released, so the total time in custody can be substantial. Because detention runs consecutively, not concurrently, with imprisonment, the real exposure of a habitual-offender case is the prison term plus the detention period. Section 21's counting rules apply, so the start and end dates should be checked precisely.
Frequently asked questions
When does the detention period start in Thailand?
Under Section 42 it runs from the date of judgment, but if the offender must serve imprisonment first, detention begins the day after release from prison.
Does detention run at the same time as a prison sentence?
No. Imprisonment is served first and detention begins the day after release, so they run consecutively, not concurrently.