Almost every open-source business-day library assumes a universal invariant: Monday through Friday are working days unless they are a fixed/Easter public holiday, and Saturday and Sunday are always weekends.
If you run payroll, NAV e-invoicing, SEPA/Giro settlement, or B2B SLA timers in Hungary (HU), that assumption breaks multiple times every single year.
How Hungarian Statutory Workday Swaps (Munkarend-áthelyezés) Work
Each year, the Hungarian Ministry for National Economy publishes an official decree announcing which Thursdays or Mondays adjacent to a Tuesday/Thursday public holiday become statutory bridge rest days (pihenőnap)—and which Saturdays must be worked in exchange (ledolgozós szombat / munkanap).
Take August 2026 around Hungary's State Foundation Day (Szent István ünnepe, Thursday, 20 August 2026):
- Saturday, 8 August 2026: Declared an official working day (
workday_swap) to make up for Friday, 21 August. - Thursday, 20 August 2026: Statutory public holiday (
State Foundation Day). - Friday, 21 August 2026: Declared a statutory bridge rest day (
bridge_rest), creating a 4-day long weekend.
// Calling POST /v1/workday-holiday/between for 2026-08-17..2026-08-24 (country: "HU"):
{
"start_date": "2026-08-17",
"end_date": "2026-08-24",
"country": "HU",
"total_days": 8,
"working_days": 4,
"weekend_days": 2,
"holiday_days": 2,
"workday_adjustments": [
{
"date": "2026-08-21",
"kind": "bridge_rest",
"name": "Bridge rest day (St. Stephen's Day)"
}
]
}Why This Matters for B2B Fintech & Compliance
When a B2B invoice or tax filing deadline is defined as "5 working days from issue date", ignoring a Saturday workday swap or a Friday bridge rest day shifts the legal deadline by 1 to 3 calendar days.
In Workday & Holiday Calculator API (/v1/workday-holiday), we maintain both the Gauss/Meeus Easter computus across 13 jurisdictions (HU, DE, AT, FR, ES, IT, NL, PL, CZ, SK, RO, GB, US) and the full 2025–2027 Hungarian ministerial bridge-rest and Saturday-workday schedule.
Pair it with Hungarian Business & Tax ID Validator (/v1/hu-business-validator) to validate 11-digit NAV Adószám, 10-digit Adóazonosító jel, Cégjegyzékszám court codes, and Hungarian 8-8-8 Giro ↔ 28-char HU IBAN conversion in under 0.2 ms.