The Taxpayer Identification Number (INN) is one of the key identifiers in the Russian tax system. It is assigned to every taxpayer — whether an individual or an organization — and is used in virtually all financial and legal documents. In this article, we'll examine the structure of the INN in detail, explain the check digit algorithm, and clarify why developers need test numbers.
What Is an INN
An INN is a unique numeric code assigned by the Federal Tax Service (FTS) to each taxpayer upon registration. The number uniquely identifies a taxpayer within Russia's tax system. Individuals are assigned an INN once, and it does not change throughout their lifetime, even if they change their surname or place of registration.
The INN is used when formalizing employment, filing tax returns, registering transactions, opening bank accounts, and in numerous other procedures. Without this number, it is impossible to fully operate within the legal framework of the Russian Federation.
INN Structure
The length of an INN depends on the type of taxpayer:
- 10 digits — for legal entities (organizations).
- 12 digits — for individuals and sole proprietors.
Organization INN (10 digits)
The structure of a ten-digit INN is as follows:
- Digits 1–2 — the code of the Russian Federation subject (region).
- Digits 3–4 — the code of the tax office that registered the organization.
- Digits 5–9 — the serial number of the entry in the territorial section of the Unified State Register of Taxpayers.
- Digit 10 — the check digit, calculated using a special algorithm.
Individual INN (12 digits)
The twelve-digit INN has a similar structure but contains more information:
- Digits 1–2 — the region code.
- Digits 3–4 — the tax office code.
- Digits 5–10 — the serial number of the entry.
- Digits 11–12 — two check digits, each calculated separately.
How Check Digits Work
Check digits serve as protection against accidental input errors. The calculation algorithm is based on a weighted sum using weight coefficients.
For a 10-digit INN, the check digit (10th) is calculated as follows: each of the first 9 digits is multiplied by its corresponding weight coefficient from the set [2, 4, 10, 3, 5, 9, 4, 6, 8], the results are summed, the sum is divided by 11, and the remainder gives the check digit. If the remainder equals 10, the check digit is set to 0.
For a 12-digit INN, the algorithm is applied twice: first to calculate the 11th digit (with coefficients [7, 2, 4, 10, 3, 5, 9, 4, 6, 8]), then for the 12th (with coefficients [3, 7, 2, 4, 10, 3, 5, 9, 4, 6, 8]).
Why Developers Need Test INNs
When developing information systems, accounting software, CRMs, and ERPs, there is often a need to test input fields, validation, and integrations. Using real INNs for testing is bad practice for several reasons:
- Personal data protection. Real INNs belong to actual people and organizations; using them in test environments violates Federal Law No. 152-FZ on personal data.
- Risk of collisions. Test data may accidentally leak into the production environment and cause problems.
- Need for a valid format. Proper testing requires numbers that pass check digit validation.
This is exactly why test INN generators exist. They create numbers with a correct checksum that don't belong to real taxpayers. Our INN generator lets you instantly generate valid test numbers for both individuals and organizations.
Legal Aspects of Test Data Generation
Generating random INNs with a valid checksum is not illegal, since the generated number is not tied to any specific person. However, such data may only be used for testing and development purposes. Using generated INNs in official documents or for fraudulent purposes is a legal offense.
INN Validation
If you need to verify the correctness of an existing INN, use our INN validator. It will instantly check the checksum and tell you whether the number conforms to the established format.
Conclusion
An INN is not just a sequence of digits — it's a structured identifier with a built-in error protection mechanism. Understanding its structure is useful for accountants, developers, and anyone working with Russian business requisites. You can generate a test INN with a valid checksum using our INN generator, and verify an existing number through the INN validator.
