💡 Executive summary
Thai company tax filing catches out most first-time founders in the same way: they assume a company pays tax once a year, the way an individual does. In reality, Thai revenue law requires a company to report and remit tax every month. Being even one day late starts accumulating penalties and surcharges that can reach six figures. This article sets out everything a director needs to know so the business grows without leaks.
SiamAccount provides corporate accounting as a one-stop service — monthly and annual filings, year-end closing, and lawful tax planning.
Why a registered company must keep accounts
Moving from sole trader to limited company is a real step up. The first thing to internalise is that your legal identity is now completely separate from the company's: company money is no longer your personal money.
That is why the Department of Business Development (DBD) and the Revenue Department require every company to keep proper books, for three reasons:
- Transparency: to evidence real income and expenditure, and prevent money laundering and tax evasion.
- Correct tax: the state calculates the company's tax base from these records.
- Assessing capability: financial statements are the company's report card. A bank reads them to judge whether you can service debt when you apply for an SME loan.
Does a company really file every month?
Yes — every month. A juristic person carries monthly obligations even in a month with no revenue at all, or before trading has begun. In those months you file a nil return so the Revenue Department knows your status.
Ignore the monthly filings and you are treated as having failed to file, and a criminal fine follows immediately.
Monthly company taxes
Monthly obligations arise whenever money moves. There are two main parts.
1. Withholding tax
When a company pays an individual or another company, it has a duty to withhold part of the payment and remit it to the Revenue Department, using these forms:
Who it covers: permanent employees (salary, bonus)
*Filed every month, even where employees earn below the taxable threshold.
Who it covers: individuals (freelancers, rent paid to a person)
*Example: hiring an individual designer — withhold 3%.
Who it covers: other companies (services, transport)
*Example: paying an advertising agency — withhold 2% or 3%.
2. Value added tax (VAT)
A VAT-registered company files P.P.30 every month, summarising input tax paid and output tax collected. In a month with zero sales, a nil P.P.30 is still required.
Also monthly: beyond tax, the company must remit employees' social security contributions to the Social Security Office by the 15th of the following month.
Half-year tax (P.N.D.51)
Paying one large tax bill at year end can strain liquidity, so companies pay an instalment mid-year on form P.N.D.51.
- How it works: you estimate the full-year net profit, then pay tax on half of it in advance — effectively a deposit.
- Watch out: the estimate must be accurate. If you understate projected profit by more than 25% without reasonable cause, the Revenue Department adds a 20% surcharge on the shortfall.
Annual tax (P.N.D.50)
At the end of the accounting year, the company calculates its actual 12-month result and files the annual corporate income tax return, P.N.D.50.
- How it works: tax is computed on taxable net profit, with any half-year tax already paid (P.N.D.51) credited against it.
- SME rates: the law is generous to SMEs. Where paid-up capital does not exceed THB 5 million and revenue does not exceed THB 30 million, the first THB 300,000 of net profit is exempt, and amounts above that are taxed on a rising scale up to 20%.
Financial statements and the auditor (CPA)
The largest piece of year-end work is preparing the financial statements. A company cannot self-file the way an individual can: the statements must be prepared by a registered bookkeeper and then audited and signed by a Certified Public Accountant (CPA).
Once the CPA has signed, the company files those statements with the Department of Business Development (DBD) through e-Filing, alongside the P.N.D.50 to the Revenue Department.
What if the company has no income?
This is where many dormant companies come unstuck. Even with zero revenue, the filings are still required.
A VAT-registered company that fails to file nil returns is fined THB 500 a month. Leave it a year and that is THB 6,000 in fines with no revenue whatsoever.
Failing to prepare and file annual financial statements with the DBD and the Revenue Department brings a summons and fines in the tens of thousands — and can leave a lasting mark on the directors' record.
What if the company is not VAT registered?
If your business is VAT-exempt, or annual revenue is still below THB 1.8 million and you have not registered voluntarily, one obligation falls away: no monthly P.P.30.
Everything else remains — withholding tax (P.N.D.1, 3, 53), the half-year and annual returns (P.N.D.51 and P.N.D.50), and full bookkeeping.
The annual tax calendar
Based on a standard accounting year of 1 January to 31 December:
| Tax / form | Deadline (e-Filing) |
|---|---|
| P.N.D.1, 3, 53 (monthly) | By the 15th of the following month |
| P.P.30 (monthly, if VAT registered) | By the 23rd of the following month |
| Social security contributions (monthly) | By the 15th of the following month |
| P.N.D.51 (half-year tax) | By 8 September |
| P.N.D.50 (annual tax) | Within 150 days of the year end, plus the e-Filing extension |
| Financial statements to the DBD | Within 1 month of the shareholders' meeting approving them |
Frequently asked questions
What does monthly company bookkeeping cost, and what is included?+
At SiamAccount, SME packages start in the low thousands of baht per month. Our corporate accounting package covers all monthly filings (P.N.D.1, 3, 53 and P.P.30) plus social security, closing off your penalty risk entirely.
How much does filing late cost?+
Two charges apply: a criminal fine (for example THB 200–500 per form once you are more than seven days late), and a surcharge of 1.5% per month on the tax due. The longer it is left, the more the surcharge compounds.
We are based in Lamphun or Lampang. Can we still work with SiamAccount?+
Absolutely. Our cloud accounting setup lets us serve clients across Chiang Mai, Lamphun and Lampang, with documents reviewable online around the clock.
Hand tax to the specialists and get your time back for the business
Set the accounting up correctly from the day the company is registered. We handle the paperwork, file on time, and produce financial statements that are ready for a bank.