PND 51: Thailand's half-year corporate tax and the 25% estimate rule

EXACCOUNTINGAccounting & tax

2 November 2026

PND 51 is Thailand's half-year corporate tax return. See who files, who is exempt, the deadline, the calculation and the 25% under-estimate rule.

PND 51 is the half-period corporate income tax return. Most companies and juristic partnerships file within 2 months of the last day of the 6-month period, and the tax paid is credited when filing PND 50. The biggest risk is estimating profit too low.

Who files, and who does not?

Companies and juristic partnerships taxed on net profit file under the form's conditions, and the Revenue Department's SME guide says a net loss or no income still requires filing.

A common exception is a new company whose first accounting period is shorter than 12 months, which does not file for that period. Check the actual start and end dates before concluding.

When is it due?

Under the law: within 2 months of the last day of the 6-month period
Online: extended to 2 months and 8 days, for deadlines through January 31, 2027

For the 2026 calendar-year period, the deadlines were August 31, 2026 on paper and September 8, 2026 online, and both have passed. The 2027 period falls outside the current notification, so check whether it is renewed.

How is PND 51 calculated?

The general case uses half of the estimated net profit for the full period, multiplied by the tax rate for your status.

Hypothetical example: a company at the general 20% rate estimates full-year profit of 800,000 baht.

Half of the estimate = 400,000 baht
400,000 × 20% = 80,000 baht

If you qualify as an SME, calculate the half-period tiered rates using the form's method rather than this example. Some businesses must use actual 6-month results instead of an estimate, so check the conditions before filing.

What if you estimate too low?

If estimated net profit falls short by more than 25% of actual net profit without reasonable cause, a 20% surcharge applies to the underpaid tax.

So entering a low profit figure is not a tax saving. It defers tax and adds the risk of paying a surcharge.

How can you estimate more accurately?

Keep monthly accounts up to date before month 6
Use actual 6-month figures as the base, then adjust for second-half work
Separate one-off income from recurring income
Record the reasoning behind your assumptions in case you need to explain them
Review again before filing if a major contract or expense appears

If documents are incomplete, start with the monthly accounting documents checklist, then estimate.

Does an auditor need to certify it?

A return calculated from an estimate does not need an auditor's name. A business that must calculate from actual 6-month profit includes the name under the form's conditions.

You can file yourself if your figures are clear. If revenue fluctuates or you are unsure about SME status, our tax team can review the figures before filing.