IČO + DIČ — legal company identifiers

Every Czech company has two distinct identifiers: IČO (Identifikační číslo organizace, 8 digits) for the legal identity at the Justice.cz registry via ARES, and DIČ (Daňové identifikační číslo, prefixed CZ + digits) for VAT when the entity is registered. PEPPOL directory code ICD 0151. Checksum algorithm publicly documented by ČSÚ.

History — from Czechoslovakia to ARES 2026

IČO has existed since 1989 — it was created under socialist Czechoslovakia by the Federální statistický úřad. At the 1993 split, the Czech Republic kept the 8-digit format and transferred it to ČSÚ. The DIČ was added at EU accession in 2004 for intra-EU VIES needs. The ARES portal, launched in 2010 then overhauled in 2014 and 2023, made the Czech Republic one of the EU's most advanced countries on company open data.

1989       | Creation of IČO in Czechoslovakia — 8 digits, managed by
           | the Federální statistický úřad (FSÚ).
           |
1993       | 1 January: Czechoslovakia split. Czech Republic keeps the
           | 8-digit IČO. ČSÚ (Czech Statistical Office) takes over
           | attribution.
           |
2004       | EU accession. Czech DIČ aligns with the VAT directive:
           | format CZ + digits (ISO prefix + IČO most often).
           |
2010       | Launch of ARES (Administrativní registr ekonomických
           | subjektů) — unified administrative registry on
           | wwwinfo.mfcr.cz.
           |
2014       | ARES overhaul — public REST API, JSON and XML, free
           | access without authentication.
           |
2018       | PEPPOL registry inscription — IČO gets ICD 0151
           | (Czech Republic IČO). PEPPOL OPC addresses in
           | 0151:NNNNNNNN.
           |
2023       | ARES v2 upgrade — GraphQL API, WebSocket for near-real-time
           | notifications. Retroactive coverage back to 1990.
           |
2024-2026  | ARES v2 reaches 3.3M registered entities (companies,
           | OSVČ self-employed, associations, foundations).

Governance — Justice.cz + ČSÚ + GFŘ

Three distinct actors manage the identifiers:

• ČSÚ (Czech Statistical Office) — attributes IČO, maintains and revokes it. Authoritative source of the identifier.
• Justice.cz (Obchodní rejstřík, commercial register) — legal registry of companies (s.r.o., a.s., k.s., v.o.s.). Publishes statutes, directors, annual accounts.
• GFŘ (General Financial Directorate) — attributes DIČ at VAT registration, maintains it via the DPH portal.

The ARES portal (Administrativní registr ekonomických subjektů) consolidates data from all three sources: MF ČR, ČSÚ and Justice.cz. It is hosted on wwwinfo.mfcr.cz and publicly accessible without authentication.

Schema — IČO checksum algorithm

IČO is an 8-digit number whose 8th position is a check digit computed from the first 7 by a mod-11 algorithm:

# IČO — Check digit calculation algorithm
# Specification: ČSÚ Methodology 2010, public on statistickyurad.cz

# Format: 8 digits total (7 significant + 1 check digit)
# Example: IČO = 12345678 (where 8 is the check digit)

def calculate_ico_check(seven_digits: str) -> int:
    """Compute the 8th position (check) from the first 7."""
    weights = [8, 7, 6, 5, 4, 3, 2]
    sum_weighted = sum(int(d) * w for d, w in zip(seven_digits, weights))
    rest = sum_weighted % 11

    if rest == 0:
        return 1
    if rest == 1:
        return 0
    return 11 - rest

# Real examples (Czech public entities)
# ČEZ a.s.            : IČO 45274649
# Škoda Auto a.s.     : IČO 00177041
# Komerční banka a.s. : IČO 45317054
# Česká spořitelna    : IČO 45244782

# Validation
assert calculate_ico_check("4527464") == 9   # ČEZ
assert calculate_ico_check("0017704") == 1   # Škoda Auto
assert calculate_ico_check("4531705") == 4   # Komerční banka
assert calculate_ico_check("4524478") == 2   # Česká spořitelna

The algorithm is public and documented by ČSÚ. Every business library in the Czech Republic implements it — every Czech ERP rejects on input an IČO with a wrong check digit. Old IČO with 7 digits (companies created before 1989) are prefixed with a zero to reach 8 positions (e.g. Škoda Auto: 00177041).

IČO/DIČ vs V4 identifiers

Adoption — ARES + ICD 0151 PEPPOL

• ARES v2 API — REST endpoint https://ares.gov.cz/ekonomicke-subjekty/rest/, JSON + XML, ~50M requests/year. No authentication, no reasonable quota.
• Justice.cz / OR API — dedicated endpoint for the commercial register, annual accounts, directors, statutes. Accessible via or.justice.cz.
• VIES check — intra-EU DIČ verification on ec.europa.eu/taxation_customs/vies/. Every Czech DIČ appears with CZ prefix.
• PEPPOL SMP — addresses in format 0151:12345678 in UBL Buyer/Seller. Automated routing via PEPPOL SML.
• EN 16931 (BT-29 / BT-46 / BT-44) — IČO and DIČ map respectively to BT-29 (Seller legal registration ID) with scheme ID 0151, and BT-46 (Seller VAT identifier).

Common pitfalls

• Confusing IČO and DIČ. IČO exists for every company. DIČ only exists if VAT-registered. Many OSVČ under threshold have only an IČO, no DIČ.
• IČO without leading zero. IČO created before 1989 are 7 digits + 1 check. Entered without leading zero, they look like 7 digits and trigger validation errors on ARES side.
• Prefixing DIČ without CZ. Czech DIČ must have the ISO prefix CZ for intra-EU flows (VIES). Without prefix, DIČ is considered "national" without EU recognition.
• Wrong PEPPOL ICD. For PEPPOL flows, the ICD is 0151 for IČO on the entity side, not 9931 (which designates Czech OPC for financial banking transactions, different context).
• Individual VAT number (rodné číslo). If the OSVČ has its DIČ based on rodné číslo (10 digits), it is personal data — ÚOOÚ (Czech DPA) has published guidance: do not display publicly.

Cross-links

• Czech Republic hub — full overview
• ISDOC — national XML standard
• DPH — VAT regimes
• Datová schránka — legal inbox
• ePodatelna — B2G inbox
• PEPPOL — European standard
• ARES — administrative registry
• Justice.cz — Obchodní rejstřík
• ČSÚ — national statistical office