The 0%, 15%, 20% Question: How Capital Structure Decides Whether Your SME Client Qualifies for Reduced Corporate Tax

Most of the tax stories in this series concern the edges of a boutique firm’s client base: multinational groups facing the global minimum tax, foreign founders using BOI incentives, clients holding digital assets. This article is about the opposite end, the ordinary Thai limited company that makes up most of a boutique accountant’s book, and a rule that quietly shapes its tax bill every year.

Thailand’s standard corporate income tax rate is 20% of net profit. A qualifying SME does not pay that rate on all of its profit. It pays a graduated rate, and whether it qualifies depends on two tests that are easy to pass, easy to fail without noticing, and checked at the end of the accounting period. The decisions that fail them are often commercial rather than tax decisions, which is exactly why an accountant needs to be in the room before they are made.

The Bands and the Two Tests

A company or juristic partnership qualifies for the reduced rates only if it meets both tests. The first is a paid-in capital test: paid-in capital must not exceed THB 5 million at the end of the accounting period. The second is a revenue test: income from selling goods or providing services must not exceed THB 30 million.

A company that passes both pays tax on net profit as follows:

Net profit (THB)	Tax rate
Up to 300,000	0%
300,001 to 3,000,000	15%
Above 3,000,000	20%

A company that fails either test pays 20% on all of its net profit for that accounting period. There is no partial credit and no sliding scale at the edge. The qualification is tested period by period, so a company that qualified last year is not guaranteed to qualify this year.

What the Bands Are Worth

The benefit is easier to see with numbers. Consider a company with paid-in capital of THB 4 million and net profit of THB 2 million.

Under the reduced bands, the first THB 300,000 is taxed at 0% and the remaining THB 1.7 million at 15%, which gives THB 255,000. Under the standard rate, the same profit would attract THB 400,000. The reduced bands save THB 145,000 in that year.

The saving grows with profit until it reaches a ceiling. For any company with net profit of THB 3 million or more, the reduced bands are worth a maximum of THB 195,000 a year compared with the flat 20% rate: THB 60,000 on the first band and THB 135,000 on the second. Losing qualification therefore costs a profitable SME up to THB 195,000 in a single year.

For a client with modest profits, that figure may be a meaningful share of what the business earns. It is also a cost that arrives without any change in how the business actually operates.

Paid-In Capital Is Not Registered Capital

The capital test looks at paid-in capital, meaning the amount shareholders have actually paid in, not the registered capital stated on the company certificate. A company may have registered capital above THB 5 million and still qualify if the amount actually paid up stays within the limit.

This distinction matters in both directions. A client who assumes that a high registered capital disqualifies them may be wrong. A client who assumes that a capital increase on paper is harmless may also be wrong, because what counts is what has been paid up by the end of the period.

The Commercial Decision That Triggers the Problem

The most common way a client fails the capital test is not an accounting mistake. It is a commercial choice made for a sensible reason.

A business may increase its capital to appear more substantial to a bank considering a loan. It may do so to satisfy a large customer’s supplier requirements, to meet a tender condition, or to prepare for a new investor. A founder may inject additional funds as equity rather than as a shareholder loan because it feels more stable. Each of these is a reasonable decision. Each, if it takes paid-in capital above THB 5 million by the end of the accounting period, removes the reduced bands for that period.

The point for the firm is timing. The conversation has to happen before the capital is paid in, not when the return is being prepared. By then the decision is made, and the only remaining option is to explain what it cost.

This is also where the tax saving has to be weighed against the commercial benefit rather than assumed to win. A larger paid-in capital may be worth more to a client than THB 195,000 in tax if it secures a loan or a contract. Or it may not. The firm’s role is to put the number on the table so the client decides with full information.

The Revenue Test Is a Separate Threshold

The THB 30 million revenue test deserves a clear explanation, partly because a similar figure appears elsewhere. The simplified e-Tax Invoice by Email route, covered earlier in this series, is available to businesses with revenue up to THB 30 million. The two thresholds are unrelated. They are set by different rules for different purposes, and meeting one says nothing about the other.

A firm should be careful not to blur them in client conversations. A client who qualifies for the simplified e-invoicing route is not thereby entitled to the reduced corporate tax bands, and the reverse is also true.

For a growing client, the revenue test is a different kind of planning point. A business approaching THB 30 million in income needs to understand that crossing the line moves the whole company to the standard rate for that period. It is not a reason to restrain growth, but it is a reason to forecast the tax effect of a strong year before it happens.

The Half-Year Prepayment

Corporate income tax is not paid only once a year. Companies file a half-year prepayment return, PND.51, based on an estimate of full-year net profit, and the annual return, PND.50, completes the position.

The estimate is where clients and newcomers get caught. A firm that prepares the half-year return from a rough guess, rather than a documented method, risks underestimating profit, and underestimation can attract a surcharge. The exact rules should be confirmed against the Revenue Department’s current requirements before advising a client on how much margin for error they have.

The sound practice is to estimate the full-year profit from the actual first-half results and known trends, record how the estimate was reached, and revisit it if the business changes materially. A documented method protects both the client and the firm if the estimate is later questioned.

The estimate also interacts with qualification. A firm projecting full-year profit should be projecting the tax position under the correct bands, which means checking whether the client will still pass both tests at the end of the period.

BOI and Other Special Cases

The standard SME analysis does not cover every client. A company with BOI privileges may receive different treatment for income from the promoted activity, so a BOI-promoted client needs a separate analysis rather than an assumption that the standard bands apply. Companies that are part of a larger group, or with unusual capital arrangements, should also be reviewed individually.

The thresholds and rates themselves are set by Revenue Department rules and can be adjusted. The bands should be confirmed each tax year rather than carried forward from last year’s return. The figures in this article reflect the commonly published framework, and a firm should verify them against the current Revenue Department announcement before relying on them for a specific filing.

What a Boutique Firm Should Do

The practical step is a short review across the client list. Identify which clients are currently within the reduced bands. Note each one’s paid-in capital against the THB 5 million limit and its revenue against the THB 30 million limit. Flag any client whose capital is close to the limit or who has mentioned a funding round, a loan application, or a tender requirement.

Then build the conversation into the annual cycle. Ask clients to tell the firm before they change their capital structure. Explain the cost in the client’s own numbers. Agree the timing of any capital injection with the tax position in mind.

None of this requires sophisticated technique. It requires noticing a rule that most business owners do not know exists, and speaking up before the decision is made.

FirmFlow and the Planning Record

The tax planning conversation about capital structure and prepayment estimates draws on figures spread across the year’s records and prior filings. FirmFlow’s matter record keeps each client’s capital history, prior-year filings, and estimating notes together, so the advice is built on the actual record rather than reconstructed from memory when the half-year deadline arrives.

A saving of up to THB 195,000 a year is not trivial for an SME, and the rule that protects it is invisible to most owners. The firm that raises it before a capital increase, rather than explaining the lost saving afterwards, is doing the kind of work that clients remember at renewal time.