How Thai Tax Years Work: Calendar vs. Fiscal Year

One of the first questions foreign business owners ask: "When is my tax year?" The answer depends on your entity type and how you've structured your business.

 

Personal Income Tax: Always Calendar Year

For individuals, Thailand uses a strict calendar year:

• Tax period: January 1 - December 31
• Filing deadline: March 31 of the following year
• No exceptions: You cannot choose a different period

If you earned income in Thailand during 2025, you file by March 31, 2026.

 

Corporate Income Tax: You Can Choose

Thai companies have more flexibility. You can select either:

Option 1: Calendar Year (Most Common)

• Tax period: January 1 - December 31
• Filing deadline: 150 days after year-end (typically May 31)
• Advantage: Aligns with personal tax, simpler coordination

Option 2: Fiscal Year

• Tax period: Any 12-month period you choose
• Example: April 1 - March 31
• Filing deadline: 150 days after your fiscal year-end
• Advantage: Can align with parent company or business cycles

 

How to Set Your Fiscal Year

You declare your fiscal year when registering your company. Once set, you generally cannot change it without Revenue Department approval.

Most foreign-owned companies choose calendar year for simplicity.

 

Half-Year Filing Requirement

Regardless of which year you choose, Thai companies must also file:

• Half-year return: Within 2 months of mid-year
• Purpose: Estimated tax payment
• Requirement: Mandatory even if no profit

 

BOI Companies: Special Rules

BOI-promoted companies follow the same calendar/fiscal year rules, but their tax exemption period is calculated from the date they start earning revenue from promoted activities—not necessarily aligned with their fiscal year.

 

Planning Tip

If you're just starting, choose calendar year unless you have a specific reason to do otherwise. It makes coordination with personal tax, accountants, and government agencies much simpler.

 

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Related Service: Accounting & Tax Compliance — We help you set up proper tax calendars and filing schedules.