Every year-end, "tax deductions" become urgent matters for working individuals. Many believe that simply purchasing funds on time or completing insurance payments suffices. However, small overlooked details can cause one to lose significant tax benefits altogether.
Thairath Money has compiled the 10 most commonly forgotten tax deduction issues for the 2025 tax year, especially during the final stretch before year-end, to help taxpayers review and checklist before filing their taxes in early 2026.
1. Purchased funds on time but money transfer delayed
To claim tax deductions for purchasing RMF, Thai ESG, and Thai ESGX funds, the transactions must be completed by 30 Dec 2025 before the asset management company's cut-off time (usually no later than 14:00). Many place orders on time, but if the money is transferred after the deadline, the transaction counts for the next tax year. Therefore, ensure the order status is "Completed," not just "Submitted."
2. Forgetting the combined retirement fund ceiling
Tax deductions are not simply proportional to how much you buy. For the 2025 tax year, many are unaware that SSF funds no longer qualify for deductions. RMF funds must be combined with
The total combined limit must not exceed 500,000 baht per year. Many people maximize individual limits but exceed the overall ceiling, resulting in partial deduction loss.
For "non-retirement fund" rights, such as Thai Sustainability Funds or Thai ESG funds, the deduction is 30% of income (capped at 300,000 baht). Similarly, Thai ESGX special sustainability funds also allow 30% of income deductions, capped at 300,000 baht.
3. Insurance premiums "paid in the wrong year"
The law considers the actual payment year, not the policy issuance year. For example, if installments are paid late in the year but deducted early next year, or if money transfer misses the year-end, deductions cannot be applied for the 2025 tax year.
4. Parental health insurance: one missed condition results in losing the entire benefit
Conditions for tax deductions on parents' health insurance include...
Any single error disqualifies the entire deduction.
5. Mortgage interest: remember to request documents from the bank
Many banks do not automatically send interest statements, especially for those who refinance or hold multiple contracts.
Therefore, you must request these important documents. Without them, you cannot fill in the details, and retroactive corrections are quite difficult.
6. Donated but not registered in the e-Donation system
Donations made via online platforms do not automatically appear in the Revenue Department's system. You must verify whether the organization is registered in the e-Donation system and has confirmation documents. Without proof, donations do not provide tax benefits.
7. Claiming deductions for parents but forgetting to check their income
Parents may have small income sources such as
and if exceeding 30,000 baht per year, the deduction is disallowed. Many only realize this after being audited.
8. Child deduction: educational status must be clear
If a child studies at university, abroad, or suspends studies, it directly affects deduction eligibility. Incorrect or unclear information and incomplete documents risk retrospective clarification requests.
Key conditions:
The legal definition of “child” includes biological children or spouse's children and legally adopted children of the taxpayer.
9. Multiple income sources but incorrect expense deductions
This error is common among freelancers, creators, or those with side incomes. The choice between standard deductions or actual expense deductions
affects the tax base significantly. The final stretch is when calculations must maximize benefits, not just input numbers.
10. Tax planning is not about last-minute deduction shopping
The reality some avoid accepting is that some people do not need to buy anything extra. If purchasing deductions causes
the tax savings may not outweigh the personal cost.
Furthermore, 2025 narrows deduction options. Missing out leads to greater tax payments, but careful planning can increase savings and personal cash retention.
Source: Revenue Department, Tokio Marine Life Insurance, setinvestnow
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