What Thai law actually requires
Every Thai juristic person — limited companies, partnerships, branch offices — must maintain books of account in Thai language, in baht, on the accrual basis, and submit them to an annual audit. The Accounting Act 2000 sets a minimum 5-year retention period for source documents and journals.
Sole proprietors don't have the same statutory bookkeeping obligation but still need clean records to file accurate personal tax returns and to support any VAT registration.
Monthly close cycle
- Collect all sales invoices, purchase invoices, receipts and bank statements within the first 5 working days of the following month.
- Reconcile each bank account against the cash ledger.
- Post payroll, social security and withholding tax journals.
- File PND.1 (payroll WHT), PND.3 / PND.53 (services WHT), PP.30 (VAT) and SPS 1-10 (SSO) by their respective due dates.
- Issue a month-end P&L and balance sheet for management review.
Source documents the Revenue Department will ask for
In a Revenue audit, the burden of proof is on the taxpayer. The auditor will compare your bank deposits to declared revenue, your supplier payments to claimed expenses, and your stated headcount to social-security filings. Any unsupported gap becomes assessed income with a 100% surcharge.
Keep tax invoices (not just receipts) for every input VAT claim — the Revenue Department disallows input VAT supported only by a receipt and not a full tax invoice.
Chart of accounts that works for SMEs
Use the standard Thai SME chart of accounts as your base — it maps directly to the year-end DBD financial statements and saves several days of audit work. Most accounting software sold in Thailand (FlowAccount, PEAK, Express) ships with a compliant chart preloaded.
When to bring it in-house
Below about 100 transactions per month, outsourced monthly bookkeeping at 3,500–8,000 THB per month is cheaper than hiring a full-time Thai bookkeeper. Above that volume, or when management needs daily cash visibility, a part-time in-house bookkeeper paired with an outsourced tax-filing service usually wins.