WHT 3% (ภงด.53): Withholding Tax Guide for Thai Calibration Labs
What Is Withholding Tax (WHT) in Thailand?
Thailand's Withholding Tax (WHT) system requires the payer to deduct a percentage of the payment at source and remit it directly to the Revenue Department on behalf of the recipient. It is effectively a prepayment of the recipient's income tax.
For calibration and testing laboratories, WHT affects you in two directions:
- As a service recipient (payer): When your lab hires external consultants, reference labs, or contractors, you must withhold tax before paying them.
- As a service provider (recipient): When a corporate client hires your lab for calibration work, they must withhold 3% and issue a WHT certificate (ภงด.53) to you.
The ภงด.53 Certificate in Practice
When clients must withhold and issue ภงด.53
When a juristic person (company or government agency) hires your calibration lab, they are required to:
- Deduct 3% from the service fee (not including VAT) before payment
- Remit the withheld amount to the Revenue Department by the 7th of the following month
- Issue a Withholding Tax Certificate (ภงด.53) to your lab as proof of deduction
Example: Client orders ฿10,000 calibration service (ex-VAT). They deduct ฿300 (3%), transfer ฿9,700 + ฿700 VAT = ฿10,400 to your bank, and give you a ภงด.53 for ฿300.
Common WHT rates
| Service type | Rate |
|---|---|
| Calibration / testing services (contracted) | 3% |
| Professional / consulting fees (individual) | 3% |
| Equipment / property rental | 5% |
| Advertising services | 2% |
How Labs Use WHT Certificates They Receive
Every ภงด.53 your lab receives from clients throughout the year is a tax credit that reduces your final corporate income tax (CIT) liability when you file your annual return.
- Collect all ภงด.53 certificates received during the year
- Reconcile against invoice records (the withheld amounts must match)
- Apply as prepaid tax credits on your annual CIT filing (ภงด.50)
When Labs Must Withhold and File
If your lab pays external parties — for example, hiring a reference lab to calibrate your working standards, or engaging an ISO 17025 consultant — you become the withholding agent. Your obligations are:
- Deduct the applicable rate on the payment date
- File ภงด.53 with the Revenue Department by the 7th of the following month (15th for e-Filing)
- Issue a WHT certificate to the payee
How LabSync Handles WHT
LabSync automatically generates a sequentially numbered WHT Certificate PDF when a payment is recorded against an invoice, and produces a monthly WHT Summary report exportable as CSV — ready for your accountant or e-Filing with the Revenue Department.
- Auto-assigns WHT certificate numbers in a gapless register
- Monthly WHT summary broken down by month and service type
- PDF certificates downloadable immediately upon payment recording
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