Which Thailand BOI tier can a project reach, and how to go higher

01Category A carries the income tax exemption; Category B mostly does not

BOI splits promoted projects into two categories. Category A carries the corporate income tax (CIT) exemption and is subdivided further — A1+, A1, A2, A3, A4 — with the exemption period and the cap changing tier by tier. Category B normally carries no CIT exemption, and offers mainly import duty relief and non-tax entitlements, with the terms of the promotion certificate governing in each case. The number of years attached to each tier moves whenever BOI revises its incentive list, so this page prints no figures; use the current official list (sources 1, 3).

The gap between tiers is not only length of period. There is a less visible dividing line: capped or uncapped. The top two tiers (A1+ and A1) have no ceiling on the amount exempted. From A2 down, the cumulative tax exempted may not exceed 100% of approved investment, excluding land and working capital, as approved by the Board. Once that allowance is used up, tax becomes payable again even if the exemption period is still running (source 2).

02The real gap between tiers: two ceilings, period and cap

The most common misreading in practice is treating two adjacent tiers with the same exemption period as much the same thing. A1 and A2 can run for the same number of years; the whole difference is uncapped versus capped. A project with strong profitability can save far more under an uncapped tier, because a capped one hits the 100%-of-investment wall first. Budget on the number of years alone and you will overstate the benefit.

One more point that feeds straight into the numbers: the exemption period and the exempted amount run from the date of first revenue from the promoted business, not the date the certificate is issued. If those two dates fall a few months apart, the window in which the exemption runs shifts by the same few months. On the timing side, see also how long a BOI application takes to reach the certificate.

How the ladder is structured:

• A1+ / A1 — longest period, no cap on the amount exempted. Aimed at upstream high-technology and R&D-driven activities.
• A2 — the period may be the same as A1, but the exempted amount is capped. This is the tier most often misread as "close enough to A1".
• A3 — shorter period, capped. High-technology activities important to national development, where some investment already exists in the country.
• A4 — the shortest period among the A tiers, capped. Lower technology content than A1 to A3, but adding value to local resources and supply chains.
• Category B — normally no corporate income tax exemption. Mainly import duty relief and non-tax entitlements.

Both ceilings tighten together as you go down the ladder. The specific periods and cap ratios move with the official list, so read the ladder as structure, not as figures. When you build long-term financial projections, put both ceilings — period and cap — into the projection and reconcile them year by year: once a capped tier's allowance is exhausted, normal tax resumes in that year.

03Three levers for reaching a higher tier

A tier is not won by how you argue it. Three things move it.

• Choice of activity item. One and the same business can often map to several promoted activity items, and a different landing point means a different tier. The first step in a tier assessment is to pin the item down precisely, not to force a business description onto whichever category looks closest. Pick the wrong item and the investment figures and the structure plan behind them may all have to be redone.
• Evidence of technology content. The stronger the technology, export, R&D and production-upgrading orientation, the more add-on incentives can be stacked. Qualifying spending on R&D, personnel training and local supplier development — measured as a proportion of sales over the preceding three years — can add exemption years on top of the base tier, and R&D spending that reaches the prescribed proportion can turn a capped tier into an uncapped one (source 1). All of this needs verifiable evidence of actual spending, not a statement of intent.
• Quality of the investment figures. BOI applies hard thresholds: a minimum investment, generally not below THB 1 million excluding land and working capital; value added generally not below 20% of revenue, 10% for some categories; a debt-to-equity ratio not above 3:1 for a new project; and the use of new machinery. A project above THB 2 billion must also submit a feasibility study (source 1). How you compute those figures decides both the base the cap is calculated on and how credible the file looks under review, so the numbers have to survive line-by-line questioning.

Location adds to this. A project in the Eastern Economic Corridor (EEC), a border special economic zone or a decentralisation target province can stack further incentives on most tiers. For a few of the highest tiers the addition takes an alternative form instead, such as a 50% reduction after the exemption period expires, and you take one or the other (source 1).

04A tier is assessed, not negotiated

One more thing worth saying plainly: the BOI incentive list is usually revised every two to three years, so the tier-to-period correspondence you look up today may already have changed by the time you file (source 3). Reaching a higher tier is not a negotiating technique. It is what the review assesses under the list in force, once the activity item, the technical evidence and the investment figures have been done properly.

Which tier your project can actually reach, how much can be stacked on top and how the cap base is computed have to be determined by our advisers after checking your actual operations, investment list, books and contract documents item by item. Get the tier assessment wrong and the whole investment projection and structure plan have to be rebuilt. Related reading: whether a wholly foreign-owned company can apply for BOI, and what our BOI service line covers.