Mikrorachunek Generator

How a Mikrorachunek Number Is Built

A mikrorachunek follows the 26-digit Polish NRB (Numer Rachunku Bankowego) format ²:

PL + check digits + 10100071222 + PESEL or NIP

Positions 1–26 are the NRB. The full IBAN form prepends the country code: PL + the 26-digit NRB = 28 characters total.

The Check Digit Algorithm

The two check digits use the ISO 7064 MOD 97-10 scheme, the same algorithm IBAN uses worldwide:

1. Take the 24-digit body: sort code 10100071 + account type 222 + the 13-digit padded identifier.
2. Append the country code as digits (P → 25, L → 21, giving 2521) and a 00 placeholder for the check digits.
3. Compute the remainder of that number modulo 97.
4. The check digits are 98 − remainder, left-padded to two digits.

Worked example with the synthetic PESEL 92070812345:

identifier (padded to 13):  0092070812345
body (24 digits):           101000712220092070812345
+ country code + "00":      101000712220092070812345252100
mod 97:                     36
check digits = 98 − 36:     62
final NRB (26 digits):      62101000712220092070812345
IBAN form:                  PL62101000712220092070812345

Code Examples

Copy-pasteable implementations. Both pad the identifier to 13 digits, build the body, and compute the check digits with MOD 97-10.

Python:

def generate_mikrorachunek(identifier: str) -> str:
    """
    Build a valid mikrorachunek from a PESEL (11 digits) or NIP (10 digits).
    For testing only — use podatki.gov.pl for real tax payments.
    """
    padded = identifier.zfill(13)                     # PESEL -> 2 zeros, NIP -> 3
    body = "10100071222" + padded                     # NBP sort code + 222 + id
    check_digits = 98 - (int(body + "252100") % 97)   # PL -> 2521, 00 placeholder
    return f"{check_digits:02d}{body}"

JavaScript / TypeScript:

function generateMikrorachunek(identifier: string): string {
  const padded = identifier.padStart(13, "0");
  const body = `10100071222${padded}`;
  // BigInt required — the 30-digit intermediate exceeds Number.MAX_SAFE_INTEGER
  const checkDigits = 98n - (BigInt(`${body}252100`) % 97n);
  return `${checkDigits.toString().padStart(2, "0")}${body}`;
}

Format check (regex):

^\d{2}10100071222\d{13}$

This matches the 26-digit NRB structure. It does not verify the check digits or the embedded identifier. Run the full calculation (or our Mikrorachunek Checker) for real validation.

Testing Scenarios

When you need synthetic mikrorachunek numbers:

• Automated test suites: populate test databases with account numbers that pass format and check-digit validation, without using real taxpayer data.
• Payment form development: test przelew podatkowy (tax transfer) fields that validate mikrorachunek structure.
• Accounting software integration: build or test integrations with Polish tax systems (JPK, e-Deklaracje) where payment-routing fields need valid sample data.
• Data anonymization: replace real mikrorachunek numbers in production database copies with structurally valid synthetic ones.

PESEL or NIP: Identifier Rules

The final 13 digits embed either a PESEL or a NIP, zero-padded:

To generate the embedded identifiers themselves, use our PESEL Generator or NIP Generator. To validate an extracted identifier, use the PESEL Checker or NIP Checker. For other Polish identifiers, see the REGON Generator.

Detecting which type is embedded:

• Positions 14–15 = 00 with position 16 non-zero → likely a PESEL.
• Positions 14–16 = 000 → likely a NIP.
• Confirm by running the identifier through its own checksum.

Common Questions

Is this the same as the government generator?

No. The official tool at podatki.gov.pl ³ retrieves your real mikrorachunek from the tax database. This tool generates random valid numbers for testing. Never use this tool’s output for an actual tax payment.

Can I use these numbers in production?

No. They are for development and testing only. The embedded PESELs and NIPs are synthetic and do not belong to real taxpayers.

How do I validate a mikrorachunek number?

Use our Mikrorachunek Checker, which runs structure validation, check-digit verification, and identifier extraction.

What’s the difference between NRB and IBAN format?

NRB is the 26-digit domestic format. IBAN prepends PL for international use (28 characters). The check digits are identical in both. The same NRB/IBAN standard governs every Polish bank account. See our IBAN Generator for the general format.