Czech Republic IČO validator
How the IČO format works
- Format
- 8 digits with a weighted mod-11 check digit
- Example
- 45274649
Things to watch for
- Older IČOs issued with fewer digits are written with leading zeros — enter all 8 digits, including the zeros
- For most Czech legal entities the VAT number (DIČ) is simply CZ followed by the IČO
- Checksum only — a pass doesn't confirm the business is registered in ARES or still trading
^[0-9]{8}$IČO (identifikační číslo osoby, formerly identifikační číslo organizace) is the 8-digit identification number assigned to companies, self-employed traders, public institutions and other organisations in the Czech Republic. Czech invoices, contracts and public registers use it to identify a business precisely, because names change and can be shared but the IČO is unique to its holder.
How the check digit works
Multiply the first seven digits by 8, 7, 6, 5, 4, 3 and 2 and add up the products. Divide the sum by 11 and subtract the remainder from 11. The result is the check digit, with two special cases: a remainder of 0 gives a check digit of 1, and a remainder of 1 gives 0.
Here it is for the example 45274649:
- 4×8 + 5×7 + 2×6 + 7×5 + 4×4 + 6×3 + 4×2 = 156
- 156 mod 11 = 2
- 11 − 2 = 9, which matches the final digit
IČO and the Czech VAT number
For most Czech legal entities, the VAT number (DIČ) is CZ followed by the IČO. That makes a valid IČO a useful first test of a company’s Czech VAT number. Individuals are the main exception. A self-employed person’s DIČ is usually based on their birth number (rodné číslo), not their IČO.
What a pass doesn’t tell you
A pass confirms the digits fit the check formula. It doesn’t prove that the IČO has been assigned, that the business appears in ARES (the Ministry of Finance’s system that draws on the official registers), or that it’s still trading. Slovakia uses the identical scheme, so a pass doesn’t tell you which country issued the number either.
Scope: Czech IČO format and checksum validation only. It doesn’t cover ARES registration or VAT status.
Content last reviewed 2026-10-11.
IČO FAQ
What should I do if an IČO has fewer than 8 digits?
Add leading zeros until it's 8 digits long. Some older IČOs are written without them, but the check-digit formula works on all eight positions, so this tool expects the full padded form. A 6-digit IČO needs two leading zeros before you check it.
Do Czech sole traders have an IČO?
Yes. A self-employed person (OSVČ) receives an IČO when they register a trade, just as a company does when it's registered, and it typically appears on their invoices. The check-digit formula is the same for every kind of holder.
Will a Slovak IČO pass this Czech check?
Yes, if it's well-formed. Czech and Slovak IČOs share the same pre-1993 Czechoslovak algorithm, so the checksum can't tell you which country issued a number. Confirm it in the business register of the right country.