Personal income tax is not always calculated from a single bank deposit total or salary figure. Start by classifying each kind of income and the rules that apply to it, then calculate eligible expenses, allowances, tax rates and tax already paid.
The linked video introduces how personal income tax is calculated. This article outlines an information-checking sequence and points to Thai Revenue Department guidance for the relevant tax forms. Allowances, deadlines and rules for different income types can change.
Start by Classifying Information; Do Not Apply a Tax Rate to All Receipts
List income for the full year using available records, such as withholding tax certificates, business income reports, interest or other income statements. Check which amounts are exempt, which must be included and how each is classified under the Revenue Code. Do not estimate tax from bank transfers before classifying them.
Core Calculation Steps
- Add income that must be included: Classify it by income type and the tax year in which it was received.
- Deduct expenses as allowed by law: The method and amount depend on the income type; the same deduction does not apply to everyone.
- Apply eligible allowances: Check the requirements and supporting documents for each allowance under the rules for that tax year.
- Calculate tax on net taxable income: Use the progressive rates in the Revenue Department’s table rather than applying the top rate to all income.
- Subtract tax credits: Account for withholding tax, interim tax payments or other eligible credits to estimate any additional payment or refund.
The Revenue Department summarizes this process in its year-end personal income tax calculation guide and publishes the income tax rate schedule. Check the rates and rules that apply to your own tax year.
Multiple Income Types May Have Additional Rules
People with business or other income beyond salary may need to check interim filing requirements or additional calculation methods based on the income type and legal thresholds. The Revenue Department describes comparing calculation methods in qualifying cases; the same method does not apply to everyone. Read its personal income tax guidance and the instructions for the form you will file.
If you sell goods online, separate sales, refunds, costs and expenses before calculating. See this guide to organizing tax information for online sellers. This article cannot determine whether a specific receipt is taxable in an individual case.
Documents to Gather Before Filing
- Salary and withholding tax certificates.
- Business or platform income summaries, with evidence of costs and expenses.
- Certificates for interest, dividends or other income.
- Evidence for allowances permitted under the law for that tax year.
- Information about tax paid during the year and previously filed returns.
Before entering information, check that names, amounts and tax years match across your documents. If a document is missing or you are unsure how income is classified, consult the Revenue Department’s guidance or a tax professional. Do not fill in amounts by guessing.
Before Submitting Your Return
- Check that you have gathered income from all sources that must be included.
- Confirm the expense and allowance rules for the relevant tax year.
- Compare the calculated tax with tax withheld or paid during the year.
- Check the current filing deadline and the form you need to use.
- Keep copies of your return, receipts and supporting documents for future reference.
File through the Revenue Department’s e-Filing system and follow the latest guidance for the relevant tax year. Do not rely on screen instructions or calendars from an older video.
Official sources: Revenue Department — year-end tax calculation · Revenue Department — tax rate schedule · Revenue Department — personal income tax · Revenue Department — e-Filing
Read next: Tax for online sellers · Accounting and tax documents for business owners