---
name: thai-invoice
description: Use this skill for any task involving Thai tax invoices, receipts, quotations, or withholding-tax certificates. Trigger whenever the user asks to: draft a Thai tax invoice (ใบกำกับภาษี), receipt (ใบเสร็จ), quotation (ใบเสนอราคา), credit/debit note (ใบลดหนี้/ใบเพิ่มหนี้), or WHT certificate (ภ.ง.ด.3/53). Also trigger for requests like "ออกใบกำกับภาษี", "ใบเสร็จ", "ใบเสนอราคา", "Thai tax invoice", "VAT 7%", "ภาษีหัก ณ ที่จ่าย", or any variation. If the context involves Thai accounting documents under Revenue Code §86/4, use this skill.
---

# Thai Tax Documents (ใบกำกับภาษี / ใบเสร็จ / ใบเสนอราคา / WHT)

## Overview
This skill drafts Thai tax invoices compliant with Revenue Code §86/4, plus quotations, receipts, credit/debit notes, and withholding-tax certificates (ภ.ง.ด.3/53). It applies the correct VAT 7% and WHT rates per category and matches Revenue Department wording. Use it whenever you need bookkeeping-grade Thai accounting documents — never improvise the legal phrasing or VAT/WHT math; pull from this skill.

## When to use
- ออกใบกำกับภาษีให้ลูกค้านิติบุคคล / individual buyers
- บันทึก ภ.ง.ด.3 (หัก ณ ที่จ่ายบุคคลธรรมดา) or ภ.ง.ด.53 (นิติบุคคล)
- เขียนใบเสนอราคา / ใบลดหนี้ / ใบเพิ่มหนี้
- Drafting English-Thai bilingual invoices for foreign buyers
- Calculating VAT-inclusive vs VAT-exclusive totals
- Computing withholding tax to deduct from a supplier payment

## Required fields — full tax invoice (Revenue Code §86/4)
A full ใบกำกับภาษี MUST contain all seven elements. Quote the Thai exactly:

1. คำว่า "ใบกำกับภาษี" ในที่ที่เห็นได้ชัดเจน
2. ชื่อ ที่อยู่ และเลขประจำตัวผู้เสียภาษีอากรของผู้ออก
3. ชื่อ ที่อยู่ ของผู้ซื้อ (+TIN ถ้ามี)
4. หมายเลขลำดับและเล่ม (ถ้ามี)
5. ชื่อ ชนิด ประเภท ปริมาณ และมูลค่าของสินค้า/บริการ
6. จำนวนภาษีมูลค่าเพิ่มที่คำนวณจากมูลค่าของสินค้าหรือบริการ แยกออกจากมูลค่าให้ชัดเจน
7. วัน เดือน ปี ที่ออกใบกำกับภาษี

Note: a short-form (อย่างย่อ) invoice can omit buyer TIN and address when issued by a retailer at the point of sale — but the seller must be approved by Revenue.

## VAT
- Standard rate: 7% (statutory rate 10%, reduced by Royal Decree — make rate a parameter; don't hardcode forever)
- VAT-exempt items (Sec 81): basic agricultural products, education, healthcare, books, public transport — DO NOT add VAT, and DO NOT issue ใบกำกับภาษี for these (use ใบส่งของ instead)
- Only VAT-registered sellers (ผู้ประกอบการจดทะเบียน VAT) may issue ใบกำกับภาษี

## Withholding tax (ภาษีหัก ณ ที่จ่าย)

| Service | Form | Rate (resident) |
|---|---|---|
| บริการทั่วไป (services) | ภ.ง.ด.3 / 53 | 3% |
| ค่าเช่าอสังหาริมทรัพย์ | ภ.ง.ด.3 / 53 | 5% |
| ค่าโฆษณา | ภ.ง.ด.3 / 53 | 2% |
| ค่าขนส่ง | ภ.ง.ด.3 / 53 | 1% |
| ค่าวิชาชีพอิสระ (lawyer, accountant, etc.) | ภ.ง.ด.3 | 3% |
| ดอกเบี้ย/เงินปันผล | ภ.ง.ด.2 | 10%/15% |

ภ.ง.ด.3 = WHT cert for individuals receiving payment. ภ.ง.ด.53 = WHT cert for juristic entities (บริษัท/ห้างหุ้นส่วน). WHT base = pre-VAT amount.

## Numbering, credit/debit notes, quotation
- Sequential invoice numbers required; reset annually optional (e.g. `INV-2026-0001`)
- ใบลดหนี้ (credit note): reference original invoice number, show reduction reason
- ใบเพิ่มหนี้ (debit note): same but for upward adjustment
- ใบเสนอราคา: not a tax document; include "ราคานี้ไม่รวมภาษีมูลค่าเพิ่ม" or "ราคารวม VAT 7% แล้ว" clearly; specify validity period (ยืนราคา 30 วัน)
- Common payment terms: "ชำระเงินภายใน 30 วันนับจากวันที่วางบิล" / "Net 30" / "เครดิตเทอม 45 วัน"
- Combined form "ใบเสร็จรับเงิน/ใบกำกับภาษี" is allowed for cash sales by VAT-registered sellers

## e-Tax Invoice & e-Receipt (ใบกำกับภาษีอิเล็กทรอนิกส์)
Revenue Department's electronic tax-document program. As of 2026 still **optional** — no mandatory rollout has been announced — but adopters got VAT/WHT deductibility incentives that ran through 31 Dec 2025. Two tracks; pick by annual revenue:

**Track 1 — e-Tax Invoice by Email** (small business, revenue ≤ 30M baht/year)
- Issue PDF/A-3 (or XML) by email to the buyer, CC the ETDA timestamp address (`csemail@etda.or.th`)
- ETDA returns a time-stamped copy to both parties — that timestamp is the legal proof of issuance
- No CA certificate required; signup via etax.rd.go.th
- Suitable for SMEs / freelancers / small ห้างหุ้นส่วน

**Track 2 — e-Tax Invoice & e-Receipt** (full system, any size; mandatory path for large firms)
- XML per RD schema, signed with a **digital signature** using a certificate from an RD-approved Certification Authority (CA)
- Submit XML to RD via Host-to-Host, Service Provider, or web upload on etax.rd.go.th — by the 15th of the following month
- Each document gets an RD-assigned reference; sequence numbers must be unique and unbroken

**Data elements** = same seven items as Sec 86/4 (above) **plus** a valid digital signature (Track 2) or ETDA time stamp (Track 1) and the seller's e-Tax registration ID. No paper original is required once issued electronically.

**Archival**: keep XML/PDF + signature/timestamp for **5 years** (Revenue Code §87/3); 7 years if under audit. Buyer may claim input VAT from the electronic copy — no paper needed.

**What changes vs paper invoice**: signing step, XML schema validation, RD upload (Track 2 only), and electronic archival. Numbering rules, content rules, and credit/debit-note rules are unchanged.

## Filing returns — ภ.พ.30 (VAT) and ภ.ง.ด.1/3/53 (WHT)
These are the monthly แบบแสดงรายการ that aggregate the invoices and WHT certificates issued during the period. From 1 Jan 2025 the Revenue Department requires WHT returns to be filed via e-Filing.

| Form | Purpose | Who/what | Filed by | Paper due | e-File due |
|---|---|---|---|---|---|
| **ภ.พ.30** | Monthly VAT return | VAT-registered seller; output VAT − input VAT | VAT registrant | 15th of next month | 23rd of next month |
| **ภ.ง.ด.1** | WHT on salary (Revenue Code §50(1)) | Employer → employees | Employer | 7th of next month | 15th of next month |
| **ภ.ง.ด.1ก** | Annual salary-WHT reconciliation | Same as ภ.ง.ด.1, full-year roll-up | Employer | end of February | end of February |
| **ภ.ง.ด.3** | WHT on payments to **individuals** (§3 ter, §50(2)) | Payer → บุคคลธรรมดา | Payer | 7th of next month | 15th of next month |
| **ภ.ง.ด.53** | WHT on payments to **juristic persons** | Payer → บริษัท/ห้างหุ้นส่วน | Payer | 7th of next month | 15th of next month |
| **ภ.ง.ด.2** | WHT on interest/dividends | Payer of interest/dividends | Payer | 7th of next month | 15th of next month |

- Late ภ.พ.30: surcharge **1.5% per month** (or fraction) on unpaid VAT, plus a fixed fine (200 baht if >7 days late)
- Late ภ.ง.ด.1/3/53: 100 baht fine if ≤7 days late, 200 baht if more; 1.5%/month surcharge on unpaid WHT
- RD has historically granted standing e-filing extensions of ~8 days past these dates — confirm the current notice before filing on the wire
- **ภ.พ.30** must be filed even in zero-sale months (nil return)

**Practical link**: every ใบกำกับภาษี you **issue** feeds the output-VAT side of ภ.พ.30; every ใบกำกับภาษี you **receive** feeds input VAT. Every WHT certificate you issue (ภ.ง.ด.3 / 53 booklet) feeds the corresponding monthly return; ภ.ง.ด.1 aggregates the WHT line on payroll slips. The skill produces the source documents — the periodic returns are a separate accounting step.

## Common mistakes
1. Forgetting to separate VAT line ("ราคารวม 1,070 บาท (รวม VAT)") — Revenue Code requires showing VAT amount distinctly on a full tax invoice.
2. Using "ใบเสร็จ/ใบกำกับภาษี" combined form when seller is not VAT-registered — only VAT-registered sellers can issue ใบกำกับภาษี.
3. Issuing ใบกำกับภาษี for VAT-exempt goods (books, fresh agricultural products) — use ใบส่งของ/บิลเงินสด instead.
4. Wrong WHT rate (e.g., 3% on rent — should be 5%; 2% on advertising — frequently confused).
5. Not issuing WHT certificate to payee within 7 days of submitting ภ.ง.ด.3/53.
6. Missing TIN on buyer side for B2B — Revenue may reject input-VAT claim.
7. Bilingual invoices that translate "Tax Invoice" but omit the Thai "ใบกำกับภาษี" — Thai law requires the Thai phrase explicitly.
8. Computing WHT on the VAT-inclusive amount — base must be pre-VAT.
9. Issuing e-Tax Invoice (Track 2) without a valid digital signature from an RD-approved CA — RD will reject the XML, and the buyer cannot claim input VAT.
10. Filing ภ.พ.30 on the 16th (or e-filing on the 24th) and triggering the 1.5%/month surcharge — the deadline is hard, not "around the middle of the month".
11. Mixing up ภ.ง.ด.3 and ภ.ง.ด.53 — ภ.ง.ด.3 is for payments to **บุคคลธรรมดา (individuals)**, ภ.ง.ด.53 is for payments to **นิติบุคคล (juristic persons)**. Wrong form = re-file.
12. Forgetting **ภ.ง.ด.1ก** (annual salary-WHT reconciliation, due end of February) — the monthly ภ.ง.ด.1 filings don't substitute for it.

## Templates
See:
- `templates/tax-invoice-full.md` — full ใบกำกับภาษี (Tax Invoice)
- `templates/quotation.md` — ใบเสนอราคา (Quotation)
- `templates/wht-certificate.md` — หนังสือรับรองการหักภาษี ณ ที่จ่าย (ภ.ง.ด.3/53)

## Calculator
`calc.py` — Decimal-based helpers:
- `calculate_vat(subtotal, rate=Decimal("0.07"))` → `{subtotal, vat, total}`
- `calculate_vat_inclusive(total, rate=Decimal("0.07"))` → backs out VAT from a VAT-inclusive total
- `calculate_wht(amount, rate)` → `{amount, wht, net_payable}`
- `WHT_RATES` constant for the common categories
- Run `python calc.py` for a self-test

Known limit: `calc.py` operates on a single transaction. It does not model return-level aggregation — e.g. summing many invoices' output VAT minus input VAT into a ภ.พ.30 total, or rolling WHT certificates into ภ.ง.ด.3/53 monthly totals. That belongs in the user's bookkeeping system, not this skill.