In Turkey, every business uses multiple identification numbers, each issued by a different authority.
These numbers are often confused but serve completely different purposes.

1) Tax Number (Vergi Numarası)

Issued by the Revenue Administration (GİB).
Used for invoicing, banking, POS applications and all financial operations.

For sole proprietors, the tax number is usually the citizen ID number.

2) Trade Registry Number (Ticaret Sicil No)

Issued by the Trade Registry Office.

Only required for:

• Limited companies

• Joint-stock companies

• Cooperatives

Not required for sole proprietorships.

Used for contracts, bank applications, official documents.

3) MERSIS Number

A digital registration number in the Central Registration System (MERSİS).

Required for:

• Company formation

• Amendments (name, capital, address)

• Digital filings

Every company has a MERSIS number, including sole proprietorships.

4) SGK Workplace Number

Issued by the Social Security Institution (SGK).
Required for any employer who hires personnel.

Used for:

• Employee registration

• Premium reporting

• Social security inspections

If a business has no employees, this number is not required.

5) Summary Table

6) Key Differences Between Sole Proprietorship and Limited

(See Turkish table — same logic applies.)

7) Conclusion

Each identification number belongs to a different authority and serves a unique function.
Understanding them helps ensure legal compliance, smooth banking operations and financial transparency.