Half-year tax return (PND 51) in Thailand.
Thai companies file a half-year corporate-tax estimate (PND 51) by the end of the eighth month of the financial year. We forecast accurately, file on time, and avoid the penalty for under-estimation.
What is the half-year report (PND 51)?
Companies subject to corporate income tax on net profit must make a mid-year prepayment of tax on form PND 51. The return falls due within two months of the end of the first six months of the accounting period. In most cases the company estimates its net profit for the full year, calculates tax on half of that figure, and pays it in advance.
That prepayment is not an extra charge — it is credited against the annual tax bill settled on the PND 50. A company expecting to make a loss for the year is not excused: the half-year return must still be filed. PND 51 is included in the monthly accounting fee — it is not billed separately.
The mechanics of the mid-year prepayment.
A handful of rules decide how much you pay, when you are exempt, and where the penalty risk lies.
Estimate method
Most companies forecast their full-year net profit and pay tax on half of that estimate at the mid-year point.
Actual method
Listed companies, banks and financial institutions pay on their actual first-half profit rather than on an estimate.
The credit
Whatever you pay on the PND 51 is offset against the annual PND 50 liability — it reduces, not adds to, the year-end bill.
First-period exemption
No half-year return is required in a company's first accounting period, or in any first period that runs for less than twelve months.
The 25% rule
Understating full-year net profit by more than 25% without reasonable cause triggers a 20% surcharge on the shortfall.
Safe harbour
Estimating at least half of the prior year's actual net profit is treated as a reasonable basis for the forecast.
When it is due, and what happens if the estimate is short.
The filing window is fixed, and the surcharge for under-estimating is avoidable with a defensible forecast.
Deadlines
- Filed within two months of the end of the first six months of the accounting period.
- For a 31 December year-end, that means by 31 August.
- E-filing adds roughly eight days — pushing the deadline to around 8 September.
- For the current cycle, the 8-day e-filing grace scheme runs until 31 January 2027 — the end date of the scheme itself, not the PND 51 filing deadline.
Penalties & safe harbours
- A 20% surcharge applies to the shortfall where full-year net profit is understated by more than 25% without reasonable cause.
- Estimating at least half of the prior year's actual net profit is a recognised reasonable basis.
- Paying at least half of the prior year's tax is likewise accepted as a reasonable basis.
Different companies, different methods.
- Ordinary companies file on an estimate of their full-year profit.
- Listed companies, banks and financial institutions file on their actual first-half profit.
- Newly formed companies skip their first accounting period where it is shorter than twelve months.
- Loss-making companies must still file a PND 51.
Filing the half-year return, step by step.
From reviewing the first-half numbers to crediting the prepayment, the process runs in five clear stages.
Review the first-half results
Close the half-year accounts and confirm the first-half actuals as the starting point.
Estimate full-year net profit
Project the full-year position — or compute the actual first-half figure, for listed companies and financial institutions.
Calculate the tax
Apply the corporate tax rate to half of the estimated full-year net profit.
File and pay
Submit the PND 51 and pay within two months of the half-year end — plus eight days if e-filed.
Credit the prepayment
Offset the amount paid against the annual PND 50 liability at year-end.
The PND 51 is the mid-year tax checkpoint. Under-estimate it by more than 25% and there's a penalty.
Thai law requires companies to estimate their full-year taxable profit at the half-year point and to file half of the estimated tax in advance. The Revenue Department compares the estimate to the year-end actual — and if the estimate understated full-year profit by more than 25% without reasonable cause, a 20% surcharge applies to the difference.
The estimate is therefore not a casual number — it needs to be defensible against the year-end outturn. We use first-half actuals, second-half forecasts, and consistent tax assumptions to build the estimate, document the working in a memo, and file the PND 51 in good time.
If circumstances change later in the year, the estimate cannot be retroactively reset — but the memo provides the audit trail showing the estimate was reasonable when made.
What we do
- Half-year close and management accounts
- Full-year profit forecast based on H1 actuals and H2 pipeline
- Tax estimate calculation including provision adjustments
- PND 51 form preparation
- Filing with the Revenue Department within deadline
- Supporting working memo for audit trail
What you get
- Estimate documented so it's defensible if challenged
- Coordinated with monthly bookkeeping for accurate H1 base
- Filed within the statutory window
How we work
Mid-year close
Half-year accounts closed; H1 actuals confirmed.
Forecasting
We work with you on H2 forecasts: pipeline, capex, hiring plans.
Estimate build
Full-year tax estimate calculated; working documented in a memo.
Filing
PND 51 filed with the Revenue Department; payment instructions issued.
Speak with our team
Send a message — typical response within one hour during office hours.
WhatsApp +66 95 332 2447 Send an Enquiry Call +66 2 026 0600Frequently asked
When is the PND 51 deadline?
Within two months of the end of the first six months of the accounting period — typically end of August for a December year-end.
What if my forecast turns out to be too low?
If the year-end actual understated the eventual full-year profit by more than 25% without reasonable cause, a 20% surcharge applies to the shortfall. The defensibility of the original estimate matters.
Can I revise the estimate later in the year?
No. The PND 51 is a single filing. Forecast accuracy at the half-year mark is therefore important.
Is this included in the accounting & tax package?
Yes.
Reviewed by the Khonsu Legal team · 1 July 2026
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