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calcthai.com · Thailand Late Tax Filing Calculator
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Thailand Late Tax Filing Calculator
Filed your Thai tax return late? Work out the 1.5% monthly surcharge and its legal cap under Section 27, straight from Revenue Department sources.
Surcharge by months late
| Late by | Surcharge | Total payable | Note |
|---|---|---|---|
| 1 months | 75.00 | 5,075.00 | — |
| 2 months | 150.00 | 5,150.00 | — |
| 3 months | 225.00 | 5,225.00 | — |
| 6 months | 450.00 | 5,450.00 | — |
| 12 months | 900.00 | 5,900.00 | — |
| 24 months | 1,800.00 | 6,800.00 | — |
| 36 months | 2,700.00 | 7,700.00 | — |
| 67 months | 5,000.00 | 10,000.00 | Reaches the cap here |
| 120 months | 5,000.00 | 10,000.00 | At the cap — no further growth |
Ask about this page
The AI assistant answers only questions about the calculator on this page.
Realising you never filed, then putting it off because you fear the number, is the loop that turns one missed deadline into several — including for foreigners who only later learn they were supposed to file in Thailand at all. This page shows the actual figure, which is usually far smaller than feared.
The surcharge runs at 1.5% of the tax per month, and the law caps it at the tax amount itself. Most importantly: if no tax was actually due, the surcharge is zero — and a large share of people who never filed fall into exactly that group.
How it works
The surcharge. Under Section 27 of the Revenue Code, tax not paid by the deadline accrues a surcharge of 1.5% per month of the tax due, with any fraction of a month counted as a full month, running from the day after the filing deadline until payment.
The cap almost nobody mentions. The total surcharge cannot exceed the tax amount itself. However late you are, the worst case is paying double the original tax — the cap is reached at 67 months. The fear of interest compounding without limit does not match the law. It is still no reason to wait: every month before the cap adds a real 1.5%.
It is calculated on the tax, not on income. Many people who never filed turn out, once the numbers are run, to owe nothing — or to be due a refund. In that case the surcharge is zero, leaving only the criminal fine for late filing, which the law caps at 2,000 baht.
About that criminal fine, plainly. The statute sets only a ceiling of 2,000 baht. The amount actually collected at the counter is settled at the officer’s discretion under internal rules. The precise figures circulating on other websites cannot be verified against any official announcement, so this page does not repeat them.
Coming forward beats being found. Everything here describes filing voluntarily. If instead the Revenue Department finds the omission and assesses you, a penalty of one to two times the tax is added on top — far larger than the surcharge. Filing yourself, promptly, is always the cheapest path.
Filing back years. The current year files online as normal. For older years, visit your area Revenue office with the income records and withholding certificates for those years; the officer calculates the surcharge and fine on the spot. Use this page to prepare the money and the nerves in advance.
One more point for foreigners: if tax was withheld from your income in those unfiled years, filing late may still produce a refund rather than a bill — refund claims stay open for three years from that year’s deadline.
Frequently asked questions
I am three months late with 5,000 baht due. What does it cost?
5,000 × 1.5% × 3 = 225 baht of surcharge, so 5,225 in total, plus the criminal fine for late filing, capped by law at 2,000 baht. If nothing was actually due, the surcharge is zero and only the fine remains.
No tax was due — does being late still cost anything?
No surcharge, since it is calculated on the tax amount, which is zero. The criminal fine for late filing still applies, capped at 2,000 baht. And if a refund was owed to you, not filing abandons it — the claim stays open three years from that year’s deadline.
I am years late. Has interest swallowed everything?
No — Section 27 caps the total surcharge at the tax amount, reached at 67 months. The worst case for voluntary filing is double the original tax. Being assessed after the Revenue Department finds the omission is a different matter: that adds a penalty of one to two times the tax on top.
Should I wait and sort it out next filing season?
No. The surcharge grows every month (fractions count as whole months), and filing voluntarily before being found avoids the one-to-two-times assessment penalty. Each year files separately anyway — waiting gains nothing.
Sources
Rates last verified 30 Aug 2026