How is the Thai tax ID check digit calculated?

Multiply each of the first 12 digits by descending weights 13, 12, ... 2 and sum them. The check digit is (11 minus (sum mod 11)) mod 10, and it must equal the 13th digit.

Is the Thai tax ID the same as the national ID?

For individuals, yes — the taxpayer identification number is identical to the 13-digit national ID card number. Juristic persons (companies and partnerships) use a separate 13-digit registration number that typically starts with 0.

What does the first digit mean?

The leading digit signals the category: 1 through 8 indicate an individual record, 0 indicates a juristic person or newer registration, and 9 indicates an older juristic registration.

Does a valid check digit mean the taxpayer is registered?

No. A valid check digit only confirms the number is internally consistent. It does not confirm active registration with the Revenue Department; verify that through the official RD e-Tax system.

Is my tax ID sent anywhere?

No. The check-digit calculation runs entirely in your browser, so the number never leaves your device.

Thailand Tax ID Validator

A Thai taxpayer identification number (TIN) is the 13-digit identifier issued by Thailand’s Revenue Department. For individuals it is the same number printed on the national ID card (บัตรประชาชน), while juristic persons such as companies and registered partnerships are assigned a separate 13-digit registration number. Before relying on a tax ID on a Thai e-Tax invoice, payroll record or supplier file, you can confirm it is internally well-formed with the Revenue Department’s check-digit rule. This free validator runs that exact check in your browser.

How it works

The 13th digit is a check digit derived from the first 12 digits:

Strip any dashes and spaces so you have 13 digits.
Multiply each of the first 12 digits by a descending weight: 13, 12, 11, … down to 2.
Add the 12 products together to get the weighted sum.
Compute the check digit as (11 - (sum mod 11)) mod 10.
The number is valid if that result equals the 13th digit.

The leading digit also encodes the record type: 1-8 for individuals, 0 for juristic persons or newer registrations, and 9 for older juristic registrations.

Example

Take a number whose first 12 digits give a weighted sum of, say, 309. Then 309 mod 11 = 1, so the expected check digit is (11 - 1) mod 10 = 0. If the actual 13th digit is 0, the number passes; any other 13th digit fails.

A valid check digit confirms the number is well-formed, not that it is registered or active. To confirm registration for e-Tax invoicing, use the official Revenue Department system. Everything here runs locally — your tax ID never leaves your device.