CORPORATE INCOME TAX PLANNING · THAILAND · JUNE 2026
Thailand’s BOI promotion is one of the most powerful corporate income tax planning tools available to foreign-owned businesses. But the rules governing loss carry forward a critical element of post-BOI tax planning operate differently depending on when losses arise. Companies that misread the timing forfeit tax relief permanently.
Thailand’s two loss carry forward regimes and why the difference matters
Thailand does not have a single loss carry forward rule. It has two, and they operate on entirely different clocks. Which one applies to a given loss is determined by one factor alone: whether that loss arose before the BOI CIT exemption began, or during it.
Under the Revenue Code (Section 65 Ter 12), losses may be offset against profits for up to five years from the year they arose. The clock starts immediately. This rule covers all pre-BOI losses and any losses from non-promoted activities.
Under the Investment Promotion Act (Section 31), losses that arise during the BOI CIT exempt period are treated differently. The five-year carry forward window does not begin until the exemption expires. The loss pool waits, however long the exemption runs. Once the exemption ends and corporate income tax applies again, the company has five full years to absorb those losses against taxable profit.
This is a statutory right. No application to the Board of Investment is required. The deduction is claimed directly in the annual PND.50 tax return.
The five-year window for pre-BOI losses runs regardless of BOI status and it will expire during the exempt period if no taxable income is available to absorb it.
Scheme one the pre-BOI loss carry forward trap
A company that incurs losses before receiving BOI promotion faces an underappreciated structural risk. Once BOI promotion begins and the CIT exemption takes effect, all profits from promoted activities become tax-free. There is no taxable income base against which to offset earlier losses. The Revenue Code clock, however, continues to run.
By the time the exemption ends, the pre-BOI losses have expired. They cannot be revived. The company then pays full corporate income tax on its post-exempt profits with no available relief.
The loss is not apparent at the time it happens. No notification is issued. Companies often discover the problem only when preparing their first post-exempt tax return, at which point nothing can be done.
| The practical consequence A company that loses money in the two years before BOI approval, then enters an eight-year exemption, will pay full CIT on its first profitable post-exempt year with no carry forward available. The losses simply expire during the exempt years, unused. |
Scheme two the BOI loss carry forward advantage
Losses that arise during the BOI exempt period itself are governed by the Investment Promotion Act rather than the Revenue Code. The fundamental difference is timing: the five-year carry forward window does not start until the exemption ends.
This means a company that records losses in the early years of a five-year BOI exemption retains the full right to use those losses beginning from the first year in which it becomes taxable again. The loss pool does not diminish during the exempt years regardless of how profitable the promoted activities become. It simply waits.
When the post-exempt period begins, the company deducts the accumulated losses from its taxable income in PND.50. No prior approval is required. The mechanism is clean, the right is absolute, and the timing advantage over the Revenue Code regime is substantial.
Three factors that determine whether the BOI loss carry forward advantage is realised
1. Whether losses are correctly declared
Losses that are not properly reported in PND.50 for the year they arose cannot be carried forward. Filing compliance during the exempt period even when no tax is owed is a prerequisite for using the loss pool post-exemption.
2. Whether promoted and non-promoted activities are segregated
Companies with both BOI-promoted and non-promoted revenues must maintain separate profit and loss accounts. The BOI loss pool applies only to promoted activities. Without proper segregation, the Revenue Department may disallow the carry forward deduction.
3. Whether post-exempt earnings can absorb the pool within five years
The five-year post-exempt window is fixed. If profits are lower than expected in the years following the exemption, part of the loss pool may expire before it is fully utilised. Modelling the earnings trajectory before the exemption ends is essential to avoid a second forfeiture.
Conclusion: timing your BOI loss carry forward in Thailand
The BOI loss carry forward is one of the most underutilised elements of corporate income tax planning in Thailand. The regime is more favourable than the standard Revenue Code but only for losses that arise in the right period. Pre-BOI losses are subject to a clock that does not wait. BOI period losses have the benefit of time.
The companies that extract the most value from BOI promotion are those that understand this distinction before losses arise not after. Proactive planning around the timing of losses, the segregation of activities, and the modelling of post-exempt earnings can represent a material difference in the effective tax rate over the full investment cycle.
Contact us for tax planning Tax planning is time-sensitive. If your company has accumulated losses during a BOI exempt period, or if your exemption is approaching its end, the window to act is limited. We advise foreign-owned companies in Thailand on BOI tax structuring, loss carry forward positions, and post-exempt CIT planning. Contact us to assess your position and quantify the tax saving available before it expires.
This article is for general informational purposes only and does not constitute legal or tax advice. Companies should seek qualified professional advice specific to their circumstances.