About BillsOS
BillsOS is a Thai invoicing and tax-compliance web app operated by Cavastir, built for freelancers and micro-businesses in Thailand. It issues tax invoices, receipts, quotations, and Section 50 Bis withholding-tax certificates (50 ทวิ) in the Revenue Department format, and generates PromptPay QR codes pre-filled with the exact amount — your client scans and pays straight into your own bank account. BillsOS never holds funds and charges no per-bill fee, and works in both Thai and English. BillsOS formats and computes documents only; it does not file returns for you and is not tax advice.
What does BillsOS do?
- Generates exact-amount PromptPay QR codes paid straight to your bank account
- Issues tax invoices and receipts in the Revenue Department format
- Creates 50 Bis withholding-tax certificates and computes VAT / withholding for you
- Quotations, and bilingual Thai/English documents
What does BillsOS NOT do?
- It is not a payment processor or e-wallet — it does not hold or move your money
- It is not a full accounting suite, and it does not file tax returns for you
- It does not provide tax advice — it only formats and computes documents
Why we built BillsOS
Most Thai freelancers and small shops do not have an accounting department, yet they still need to issue documents in the format the Revenue Department expects — tax invoices, receipts, and a 50 Bis certificate every time tax is withheld. We found existing tools were either full accounting suites (more than most people need) or did not support PromptPay and English for overseas clients. BillsOS is built to do one thing well: create correctly formatted, correctly calculated documents fast, straight from a browser, with nothing to install.
How BillsOS documents map to Revenue Department formats
For transparency, here is what BillsOS generates, mapped to the name and form the Revenue Department uses:
| Document in BillsOS | Maps to | Used when |
|---|---|---|
| Tax invoice | Tax invoice under section 86/4, Revenue Code | A VAT-registered seller sells goods or services |
| Receipt | General receipt of payment | Confirms payment was received, VAT-registered or not |
| Withholding-tax certificate (50 Bis) | Certificate under section 50 bis, Revenue Code | A payer withholds tax on a service fee, rent, etc. |
| Quotation | Not a tax document — a pre-sale price quote before the invoice/receipt | Before a client confirms a job |
BillsOS formats and calculates the numbers (VAT, withholding) to match the Revenue Department’s rules, but choosing the right document type and filing your returns remain your responsibility. If unsure, check with the Revenue Department (rd.go.th) or your accountant.
Trust & disclaimer
BillsOS is operated by the Cavastir team. We build our guides and tools from the Thai Revenue Department’s published rules and keep them current. The information on this site is general information to make Thai tax easier to understand — it is not individual tax, legal, or accounting advice. Please confirm with the Revenue Department (rd.go.th) or your accountant before making any decision with tax consequences.
See the full breakdown of costs on our pricing page, and browse our Thai tax answers hub.
How to contact us
Email: support@billsos.com · Contact page