An estimated profit shortfall of more than 25% is the situation in which a company or juristic partnership files its half-year corporate income tax return (P.N.D.51) showing an estimated full-year net profit that is more than 25 percent below the actual net profit at the end of the accounting period, under Section 67 ter of the Revenue Code. If the business does not qualify for the "reasonable cause" exemption, the Revenue Department immediately assesses a surcharge of 20% of the tax underpaid. This is an additional tax burden that directly affects the business's liquidity.
For the 2026 accounting period, many operators, especially service, retail and tourism businesses, find that revenue in the final quarter rises far above what they forecast in the first half. This article summarizes the legal rules, how to calculate the shortfall, the exemptions under the Revenue Department's instructions, and how to correct the situation before the end of the accounting period, so that your business can plan its taxes correctly and safely.
Why an Estimated Profit Shortfall of More Than 25% Affects Your Business
Section 67 bis of the Revenue Code requires a juristic person that pays income tax on net profit to prepare an estimate of its net profit or net loss for that accounting period, calculate the tax, and pay half of the tax on the estimated net profit within 2 months of the last day of the first 6 months of the accounting period (for a normal calendar-year period, by 31 August).
If the actual result at the year-end close (P.N.D.50) shows that the estimated net profit fell short by more than 25 percent of the actual net profit, the business is affected under Section 67 ter as follows:
- A 20% surcharge: the business must pay a flat surcharge of 20% of the amount of tax underpaid, or of half the tax payable for that year. This is a fixed rate that applies immediately, with no pro-rating by time as with the usual monthly surcharge.
- It is a non-deductible expense: a surcharge paid to the Revenue Department is a non-deductible expense under Section 65 ter (6) and cannot be deducted when calculating net profit for tax.
- Risk of a retrospective tax audit: an estimated profit shortfall of more than 25% without reasonable cause is one of the screening criteria for irregularities in the tax supervision system, which may lead to a detailed document inspection and stock count.
How to Calculate the 25% Shortfall, with a Real-World Example
To check whether the estimated net profit filed in P.N.D.51 falls below the threshold the law allows, use the comparison formula set out in the Revenue Department's guidelines:
Shortfall ratio formula:Shortfall percentage = [(actual full-year net profit - estimated net profit filed in P.N.D.51) ÷ actual full-year net profit] × 100
Worked Example: A Café and Coffee Roastery in the Nimman Area, Chiang Mai
Nimman Roastery Co., Ltd. sells beverages and processed coffee beans in Chiang Mai. Its accounting period runs from 1 January to 31 December 2026, its paid-up registered capital is 2 million baht and its total annual revenue does not exceed 30 million baht, so it qualifies as an SME juristic person (tax rates: the first 300,000 baht of profit is exempt; profit above 300,000 up to 3,000,000 baht is taxed at 15%). Its tax figures are as follows:
- Mid-year P.N.D.51 filing:
- Estimated full-year net profit for 2026 = 800,000 baht
- Full-year tax on the SME basis = (800,000 - 300,000) × 15% = 75,000 baht
- Half of the tax paid with P.N.D.51 = 75,000 ÷ 2 = 37,500 baht
- Actual result at the end of the accounting period (P.N.D.50):
- Actual full-year net profit after tax adjustments = 1,500,000 baht
- Actual full-year tax on the SME basis = (1,500,000 - 300,000) × 15% = 180,000 baht
- Half of the tax that should have been paid for the half-year = 180,000 ÷ 2 = 90,000 baht
- Calculate the shortfall ratio:
- [(1,500,000 - 800,000) ÷ 1,500,000] × 100 = 46.67% (over the 25% threshold)
- Calculate the 20% surcharge under Section 67 ter:
- Half-year tax underpaid = 90,000 - 37,500 = 52,500 baht
- 20% surcharge = 52,500 × 20% = 10,500 baht
Year-end tax summary: the company must pay the remaining tax of 142,500 baht (180,000 - 37,500) with its P.N.D.50 return, plus a surcharge of 10,500 baht, for a total payment of 153,000 baht.
Legal Exemptions: What Counts as "Reasonable Cause" So No Surcharge Is Due
Under Revenue Department Instruction Por. 50/2537 and the Department's rulings, if a juristic person meets the conditions for "reasonable cause", it is exempt from the 20% surcharge even though its estimated net profit fell short by more than 25 percent. The key criteria are:
| Criterion | Details of the legal condition | Tax result (20% surcharge) |
|---|---|---|
| Safe harbor (half of the previous year's tax) | The estimate and half-year tax payment are not less than half of the corporate income tax payable for the previous accounting period (the previous period must have been a full 12 months) | Treated as reasonable cause: exempt from the 20% surcharge, with no condition on the profit difference |
| Shortfall of not more than 25% | The estimated net profit falls short by not more than 25 percent of the actual net profit at the end of the accounting period | Meets the normal rule: no surcharge is due |
| Economic force majeure or extraordinary income | Extraordinary income arises in the second half of the year that could not have been foreseen, such as dividends received, the sale of a major asset, interest received or severe exchange-rate swings (clear evidence is required) | Can be used to prove reasonable cause and request exemption from the 20% surcharge |
Limitation on using the safe harbor: if the business had a net tax loss in the previous accounting period (so that the previous year's tax was 0 baht), the company cannot rely on paying half of the previous year's tax as 0 baht. In that case the business must prepare its 2026 net profit estimate based on the facts and keep the shortfall within 25%.
How to Fix It When You Realize the Estimate Is Short by More Than 25% Before the Period Ends
If you are in the third or fourth quarter and your internal financial statements show revenue and profit growing well beyond the estimate in P.N.D.51, you can take corrective action in advance to limit the financial damage, as follows:
- File an additional P.N.D.51 before the end of the accounting period: a juristic person can file an additional P.N.D.51 to raise the estimated net profit and pay the additional tax difference before the last day of the accounting period (before 31 December for a normal period)
- An additional filing before the period ends attracts a surcharge under Section 27 of only 1.5% per month (or part of a month) of the additional tax paid, counted from the day after the P.N.D.51 filing deadline until the date of payment
- Comparing the surcharge: in the example above, if the tax underpaid is 52,500 baht and the additional return is filed in November (counting 3 months: Sep, Oct, Nov), the surcharge under Section 27 is only 2,362.50 baht (52,500 × 1.5% × 3), saving as much as 8,137.50 baht compared with the 20% surcharge (10,500 baht) at year end
- Check tax incentives and year-end investments: review the tax incentives under government promotion measures for 2026, such as investment in machinery, automation, research and development, or staff training that qualifies for extra expense deductions, and use them in tax planning so that taxable net profit stays in line with the estimate
- Analyze the trial balance and forecast profit ahead of time: consult a professional accountant to close the monthly trial balance continuously and review the tax reconciliation figures. See the corporate tax planning service page for practical guidance
Common Mistakes and How Chiang Mai Accounting Experts Prevent Them
From our experience handling corporate taxes in northern Thailand and Chiang Mai, the main mistakes that lead to a surcharge for underestimated profit are:
- Ignoring seasonality: tourism businesses, hotels, restaurants and souvenir shops in Chiang Mai usually earn moderate revenue in the first half of the year but peak in the fourth quarter (high season). Doubling the first 6 months' revenue and profit to file P.N.D.51 therefore almost always produces an estimate that is more than 25% below reality
- Confusing accounting profit with taxable profit: businesses often enter the accounting net profit in P.N.D.51 without adding back tax adjustments, such as entertainment expenses above the 0.3% ceiling under Ministerial Regulation No. 143, depreciation on passenger cars above the 1 million baht cost cap, penalties and surcharges, or non-deductible expenses under Section 65 ter. As a result, taxable profit at year end is far higher than estimated
- No monthly management accounts: a business that does not keep its books and financial reports up to date does not know its true financial position until the year-end close, and so loses the chance to file an additional P.N.D.51 and avoid the 20% surcharge
Frequently Asked Questions About an Estimated Profit Shortfall of More Than 25%
What can you do if you discover the estimate is short by more than 25% after the accounting period has closed?
Once the accounting period has ended (after 31 December for a normal period), the law does not allow an additional P.N.D.51 to be filed to reduce the surcharge. The business must file P.N.D.50 within 150 days of the period end, pay the remaining tax and calculate the 20% surcharge under Section 67 ter on the half-year tax underpaid. Before doing so, check whether the business qualifies for the exemption of having paid not less than half of the previous year's tax (safe harbor), or has documents proving reasonable cause.
A company in its first year earns a large profit at year end. Will it be hit with the shortfall surcharge?
If the company's first accounting period is shorter than 12 months, Section 67 bis paragraph two exempts it from filing P.N.D.51, so there is no shortfall surcharge. But if the first accounting period is exactly 12 months, the business must file P.N.D.51 as normal. Because there is no previous year's tax base for the safe harbor, it must estimate its net profit as close to reality as possible and keep the shortfall within 25%; otherwise the 20% surcharge applies.
Can the 20% surcharge under Section 67 ter be reduced or waived?
The surcharge under Section 67 ter is a fixed-rate surcharge set by statute, not a penalty, so the assessment officer has no discretion to waive or reduce it under Section 22. The only way to avoid it is for the business to meet the safe harbor (half of the previous year's tax) or to have clear evidence proving reasonable cause under Revenue Department Instruction Por. 50/2537.
How many extra days do you get for filing P.N.D.51 online (e-Filing)?
Filing and paying P.N.D.51 through the Revenue Department's e-Filing system extends the deadline by 8 days from the statutory due date. For example, if the accounting period ends on 31 December, the normal filing deadline is 31 August; filing online, you can file and pay up to 8 September.
Summary: Managing Half-Year Tax Safely
You can guard against an estimated profit shortfall of more than 25% by estimating revenue and expenses realistically, especially in businesses with seasonal revenue swings. If tax was payable the previous year, use the rule of paying not less than half of the previous year's tax as your safe harbor shield. If your financial statements show growth beyond target, file an additional P.N.D.51 before the end of the accounting period to turn the 20% surcharge into only 1.5% per month.
If you are looking for help with accounting and tax, choose a Chiang Mai accounting service that understands the local business context, works through a convenient and fast online accounting system, and provides close advice. See the details at full-service accounting so that your business can grow steadily and in full compliance with tax law.
Contact YMTD Accounting Partner Chiang Mai
Tel: 081-542-3019
LINE: @premwittawat
