Personal Tax: Common Mistakes to Avoid

Personal income tax filing mistakes can cost you money—either through penalties or missed refunds. Here are the most common errors and how to avoid them.

 

Mistake #1: Not Filing When Required

The Error: Thinking you don't need to file when you actually do.

Common scenarios:

• "I only worked 6 months" (still must file)
• "My employer withheld tax" (should file to confirm/get refund)
• "I'm not Thai" (irrelevant—180-day rule applies)

Consequences:

• Late filing penalty: 1,000-2,000 THB
• Late payment penalty: 1.5% per month
• Potential criminal charges for intentional evasion

 

How to Avoid:

• Review "Who Must File" criteria
• When in doubt, file anyway
• Cost of filing (even if not required): Minimal
• Cost of not filing (when required): Significant

 

Mistake #2: Missing Deductions

The Error: Not claiming all eligible deductions, resulting in overpayment.

Commonly missed:

• Life insurance premiums (100K limit)
• Health insurance (25K limit)
• Provident fund contributions
• Home loan interest (100K limit)
• Parent allowances (30K each)
• Donations (10% of net income)

Lost money:

• Missing 200K in deductions
• = 30,000-50,000 THB overpaid tax

 

How to Avoid:

• Review full deduction checklist
• Keep all receipts year-round
• Consult with accountant
• Use tax planning software

 

Mistake #3: Incorrect Income Reporting

The Error: Not reporting all income sources.

Commonly unreported:

• Freelance income
• Rental income
• Investment income
• Foreign income (if remitted to Thailand)
• Side business income

Risk:

• Revenue Department has data from:
  • Banks (interest, dividends)
  • Employers (salary)
  • Property records (rental)
• Cross-checking is automated
• Discrepancies trigger audits

 

How to Avoid:

• Report ALL income sources
• Keep records of all earnings
• Declare foreign income if remitted
• Better to over-report than under-report

 

Mistake #4: Wrong Tax Residency Status

The Error: Claiming non-resident status when you're actually a resident (or vice versa).

180-day rule:

• Spent 180+ days in Thailand = Resident
• Must report worldwide income (if remitted)
• Different tax treatment

Example:

• Spent 185 days in Thailand
• Claimed non-resident status
• Didn't report foreign income remitted to Thailand
• Result: Tax evasion charge

 

How to Avoid:

• Count your days carefully
• Include partial days
• Keep travel records
• When close to 180, consult advisor

 

Mistake #5: Forgetting Spouse/Child Allowances

The Error: Not claiming allowances for dependents.

Lost deductions:

• Spouse: 60,000 THB
• 2 children: 60,000 THB (30K each)
• Total: 120,000 THB
• Tax savings: 18,000-30,000 THB

 

How to Avoid:

• Review all allowance categories
• Gather required documents:
  • Marriage certificate
  • Birth certificates
  • Parent ID cards (if claiming)

 

Mistake #6: Double-Claiming with Spouse

The Error: Both spouses claiming the same deduction.

Example:

• Both claim child allowance for same child
• Both claim parent allowance for same parent
• Both claim home loan interest

Result:

• System flags duplicate claims
• Both returns rejected
• Must amend and resubmit

 

How to Avoid:

• Coordinate with spouse before filing
• Decide who claims what
• File jointly if beneficial
• Keep records of allocation

 

Mistake #7: Missing the Deadline

The Error: Filing after March 31 (or May 31 for e-filing).

Penalties:

• Late filing: 1,000-2,000 THB
• Late payment: 1.5% per month on unpaid tax

Example:

• Tax owed: 50,000 THB
• 3 months late
• Penalty: 50,000 × 1.5% × 3 = 2,250 THB
• Plus: Late filing fee 2,000 THB
• Total: 4,250 THB extra

 

How to Avoid:

• Mark deadline on calendar
• Set reminders (60, 30, 7 days before)
• File early (March-April)
• Use e-filing for extended deadline

 

Mistake #8: Poor Documentation

The Error: Claiming deductions without proper supporting documents.

Audit scenario:

• Claimed 100K life insurance deduction
• Revenue Department requests proof
• Can't provide receipts
• Result: Deduction disallowed, tax recalculated + penalties

 

How to Avoid:

• Keep ALL receipts
• Scan and store digitally
• Organize by category
• Retain for 5 years

 

Mistake #9: Incorrect Bank Account for Refund

The Error: Providing wrong bank account number for refund.

Result:

• Refund can't be deposited
• Must visit Revenue Department to correct
• Delays refund by months

 

How to Avoid:

• Double-check account number
• Verify bank name and branch
• Use account in your name
• Confirm before submitting

 

Mistake #10: Not Keeping Filed Return

The Error: Losing confirmation of filed return.

Problems:

• Can't prove you filed
• No record for future reference
• Difficult to amend if needed
• Issues with visa extensions, loans

 

How to Avoid:

• Download filed return (PDF)
• Save confirmation number
• Print and file physically
• Store digital copy in cloud

 

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