For companies operating in Thailand, tax compliance is a year-round responsibility, not just a year-end task. One critical milestone is the half-year corporate income tax (CIT) filing, which ensures the Revenue Department collects tax revenues evenly across the year and that companies plan their tax liabilities effectively.
If your company has a financial year ending on 31 December, you must file its half-year CIT return (Form Por Ngor Dor 51) by 31 August 2025. For e-filing, you will get a short extension until 8 September 2025. Missing either deadline may cause penalties and surcharges. Here’s what you need to know, and how to prepare.
Note: If your company’s accounting period began on 1 December 2024, you must file your half-year CIT return by 31 July 2025 and the e-filing deadline is 8 August 2025.
What is half-year Corporate Income Tax (CIT)?
Under Section 67 bis of the Revenue Code, companies are required to file a half-year corporate income tax return (Form PND 51) and pay tax on a preliminary estimate of the year’s net profit. This estimate must be based on actual operational results for the first six months of the accounting year.
Unlike the year-end CIT (Form PND 50), the half-year return is more like a tax forecast, but with real financial data up to the halfway point of your fiscal year.
Who Must File?
The following entities must file half-year CIT:
- Companies and juristic partnerships established under Thai law
- Foreign companies carrying on business in Thailand
- Branches and representative offices of foreign entities
Exceptions include companies exempt from corporate tax or inactive/dormant companies with zero activity.
Key Dates to Remember
| Filing Type | Form | Due Date |
| Half-Year CIT Filing | PND 51 | 31 August 2025 (paper filing) |
| E-Filing | PND 51 | 8 September 2025 (extended online deadline) |
✅ Note: This applies to companies whose accounting period ends on 31 December 2024.
How Is Half-Year CIT Calculated?
The half-year tax payable is based on:
- Estimated full-year net profit, derived from the actual profit of the first 6 months
- 50% of the full-year tax liability, calculated using the 20% corporate tax rate
Formula:
(Net profit from first 6 months × 2) × 20% × 50% = Half-Year CIT payable
Example:
- First 6-month profit = THB 1,000,000
- Estimated annual profit = THB 2,000,000
- Estimated full-year tax = THB 400,000
- Half-year tax = THB 200,000
What Happens If You Underestimate?
If your actual year-end tax (PND 50) exceeds your half-year tax payment by over 25%, your company may be subject to a surcharge of 20% on the shortfall.
Tip: Be realistic with your profit estimates. Underestimating the need to conserve cash could cost you later.
What to Prepare Before Filing
To meet the deadline and avoid costly penalties, make sure to:
✅ Close your books for the first 6 months of the fiscal year
✅ Prepare management accounts and financial statements
✅ Estimate your full-year profit based on current trends
✅ Calculate the half-year tax liability (use a tax consultant if needed)
✅ File Form PND 51 and pay the tax—online or at the District Office
✅ Keep documentation to support your estimates
How to File and Pay
You can submit PND 51 and make payment:
- Online via the Revenue Department’s e-filing portal (https://efiling.rd.go.th/)
- In person at the District Revenue Office
E-payment options include bank transfers, credit cards (subject to limits), and payment at designated banks.
Penalties for Non-Compliance
| Issue | Penalty |
| Late Filing | THB 2,000–THB 5,000 fine |
| Late Payment | 1.5% interest per month (max 100%) |
| Underestimation (over 25% shortfall) | 20% surcharge on the difference |
Final Thoughts
Filing your half-year corporate income tax is more than just ticking a compliance box; it’s part of sound financial planning. By estimating your annual profit early, you get better visibility into cash flow and reduce the risk of a large year-end tax bill.
At AO Accounting & Advisory, we help both foreign and Thai companies stay compliant with Thailand’s tax laws, ensuring timely filings and mitigating risks. If you’re unsure how to approach this year’s PND 51 filing, don’t wait until the last minute.
📩 Contact our advisory team today and let us help you manage your mid-year tax filing smoothly.