What Documents Your Thai Accountant Needs Each Month

Working with a Thai accountant goes smoothly when both sides know what is expected. Many business owners in Thailand, particularly those running foreign-owned companies or small operations on Koh Samui, lose time and money simply because documents arrive late, incomplete, or in the wrong format. This guide walks you through exactly what your accountant needs from you each month, why each item matters, and how to make the handover as straightforward as possible.

Understand Why the Monthly Deadline Exists

Thailand's Revenue Department sets firm deadlines for VAT returns, withholding tax filings, and social security contributions. Most of these fall between the 7th and 15th of the following month, depending on whether you file online or in person. Your accountant needs time before those deadlines to review figures, reconcile accounts, and prepare the submission. If your documents arrive on the 12th and the filing is due on the 15th, there is very little room for errors or missing information. Getting into a rhythm of sending documents in the first few days of each month protects you from penalties and keeps your compliance record clean.

Sales Records and Tax Invoices Issued

Your accountant needs a complete record of every sale your business made during the month. For VAT-registered businesses, this means copies of all tax invoices you issued to customers. Each invoice must show your company's tax ID number, the customer's details if they are a business, the amount before VAT, the VAT amount, and the total. If you use accounting software or a point-of-sale system, export the sales report for the month and include it alongside the individual invoices. If you issued any credit notes or made any adjustments to previous invoices, include those too. Gaps in your sales records will directly affect your VAT output tax calculation and can trigger questions from the Revenue Department.

Purchase Invoices and Expense Receipts

Every expense your business incurred during the month needs documentation. This includes supplier invoices, utility bills, rent receipts, professional service fees, and any other costs related to running the business. For VAT-registered businesses, only tax invoices from VAT-registered suppliers can be used to claim input VAT, so it is worth getting into the habit of always asking suppliers for a proper tax invoice rather than a simple receipt. Keep originals where possible, or high-quality scans if you are submitting digitally. Your accountant will use these to calculate your VAT input tax, record your expenses accurately, and ensure your profit figures reflect the true cost of running the business.

Bank Statements for All Business Accounts

Provide a full bank statement for every business account for the month in question. This includes any savings accounts linked to the business, not just your main operating account. Bank statements allow your accountant to reconcile payments and receipts against your invoices, spot any transactions that have not been documented separately, and flag anything unusual. If you made transfers between accounts, paid a supplier directly from a personal card, or received a payment into the wrong account, note these separately when you send the statements. Unexplained transactions take time to investigate and can delay your filing. If your bank offers downloadable PDF or CSV statements, these work well and reduce the chance of figures being misread from a photograph.

Payroll Information and Employee Records

If you have employees, your accountant will need payroll data each month to handle withholding tax on salaries and social security contributions. This typically means a breakdown of each employee's gross salary, any bonuses or additional payments made that month, and any deductions. If you manage payroll yourself, send a simple spreadsheet with this information. If your headcount changed during the month, for example someone joined or left, flag this clearly because it affects both the withholding tax and social security calculations. Social security filings in Thailand are due by the 15th of the following month, so this information is time-sensitive in the same way as your VAT documents.

Anything That Changed or Was Out of the Ordinary

Beyond the routine documents, your accountant needs to know about anything that happened during the month that falls outside normal business activity. This could include a large one-off purchase such as equipment or a vehicle, a loan received or repaid, a foreign currency transaction, a refund issued to a customer, or a payment made in cash rather than by bank transfer. You do not need to know the accounting treatment for these things yourself. You just need to mention them and provide supporting documents. A short note or voice message describing what happened and why is often enough for your accountant to handle it correctly. Surprises discovered during year-end audits are far more expensive to resolve than issues flagged at the time they occur.

How to Send Documents in a Way That Actually Helps

The format and organisation of what you send matters almost as much as the content. Create a simple folder for each month, either physically or in a cloud storage service, and separate documents into clear categories such as sales, purchases, bank, and payroll. Name files in a way that makes them easy to identify, for example using the supplier name and invoice date rather than a generic filename like scan001. If you are sending physical documents, keep originals in order and avoid folding or stapling items that need to be stamped by the Revenue Department. Many accountants in Thailand now accept and prefer digital submissions, which also gives you a backup copy of everything. Agree on your accountant's preferred method early in the relationship and stick to it consistently. A predictable monthly routine, where documents arrive in good order at roughly the same time each month, is genuinely one of the most useful things you can do to keep your accounting costs manageable and your compliance straightforward.