How to use
Two modes share the same form. **Count** mode takes a start and end date and reports the number of business days between them, excluding weekends (Saturday + Sunday) and any country-specific public holidays on the selected calendar. **Add** mode takes a start date and a number `N`, and reports the date that is exactly `N` business days later — Monday + 5 business days = next Monday (assuming no holidays fall in between).
Reach for this when calculating an SLA, an invoice due date, a contract deadline, a payroll cutoff, or a "delivery within 5 business days" promise. Choose the country (Korea, Japan, US, UK, etc.) to apply that jurisdiction's public holiday list — Korean Chuseok and Seollal block 3–4 days of working time, Japanese Golden Week takes a full week off, US Thanksgiving is a 4-day stretch. The calendar data is bundled with the tool; nothing is uploaded or fetched.
FAQ
What counts as a "business day"?
Monday through Friday, excluding public holidays in the selected jurisdiction. Saturdays are *not* business days in this tool, even though many businesses (banks, retail) actually operate then. The "Monday–Friday only" convention is the contractual default — phrases like "delivery within 3 business days" almost always mean weekday days. For industry-specific calendars (financial markets close on additional days, retail counts Saturday but not Sunday), pick the closest country match and add or subtract days manually.
Which countries does the holiday calendar cover?
The bundled calendars include Korea (`KR`), Japan (`JP`), USA federal (`US`), UK England-and-Wales (`GB-ENG`), and a handful of other major markets. Each is the *public* holiday list — banks closed, government offices closed — which usually aligns with the business-day calendar but not always (post offices and some retail stay open on minor holidays). The data is sourced from each country's official calendar (Korea Public Holidays Act, Japan 国民の祝日に関する法律, US OPM federal holidays). Holiday observation occasionally moves between calendar years (substitute holidays in Korea, observed-on-Monday holidays in the US); the tool tracks those rules.
Should the start date count?
There are two reasonable conventions and contracts differ. **Inclusive of start**: 2 business days from Monday = Tuesday (counting Monday as day 1). **Exclusive of start**: 2 business days from Monday = Wednesday (counting Tuesday as day 1). This tool uses inclusive — what most people mean casually. Legal contracts often specify "2 business days after the date of this notice" which is exclusive of the notice day. Check the contract language; if it says "from", that is usually inclusive; if it says "after", usually exclusive.
How do Korean substitute holidays work?
Korea's **대체공휴일** (substitute holiday, formalized 2014) makes the next non-weekend day a paid holiday when a major public holiday falls on a Sunday — and since 2021, also for some holidays falling on Saturday. So Independence Movement Day (March 1) on a Sunday means March 2 (Monday) is a substitute holiday. Lunar New Year and Chuseok have always carried their three-day blocks (eve + day + day after) and now also get substitutes when any part falls on a Sunday. The tool encodes the current rule (2021 expansion). Pre-2014 dates do not get substitutes.
What if my business operates on Saturdays?
The tool treats Saturday as non-business. For a Saturday-operating business (retail, hospitality, some banks), the calculated "business days" will undercount by however many Saturdays fall in the range. The simplest workaround: count using the tool, then add the number of Saturdays in the same range (which equals the calendar days divided by 7, rounded according to which day the range starts on). For complex industry calendars (markets, religious observances, regional differences within a country), a country-level tool will always be imprecise; consider a dedicated industry calendar or a bespoke ruleset.
Why is "5 business days" different in different countries?
Because the holiday density differs. France has 11 national holidays, Korea ~15 (including the 3-day Lunar New Year and Chuseok blocks), Japan 16 (heavily concentrated in Golden Week and Silver Week), the US 11 federal holidays, the UK England/Wales 8. Concentrated holiday clusters (Korea's holidays + bridge days, Japan's Golden Week, US Thanksgiving stretch) can lengthen a "5 business days" promise by a week or more around the cluster. International contracts often specify the relevant country's calendar to avoid ambiguity: "5 business days as observed in Frankfurt" pins it to the German banking calendar.
Related concepts
A "business day" or "working day" is a calendar convention rather than a physical reality — it encodes which days a typical business is expected to operate. The default Monday-through-Friday plus public holidays is the de facto international standard for contracts, government deadlines, and shipping promises. Different industries layer their own variants: financial markets close on additional days (US Christmas Eve early close, Tokyo Stock Exchange has separate trading calendar), banks observe non-uniform local holidays, religious workplaces follow their own calendar (Saturday Sabbath in Israel, Friday prayer in Saudi Arabia).
The **public holiday list** is itself a moving target. Korea's Public Holidays Act has been amended four times since 2010, expanding substitute holidays. Japan added Mountain Day (山の日) in 2016. The US has not added a federal holiday since Juneteenth in 2021. Each amendment changes the calendar prospectively, so a holiday calculator needs versioned data — what was the Korean public holiday count in 2014 differs from 2026, and tools tracking historical dates need historical rules. The IANA-equivalent for holidays is the `nager.at` API and the `python-holidays` package, both updated whenever a government announces changes.
Three adjacent concepts shape contractual time. **T+N settlement** is the financial-industry version: stock trades settled at T+2 in the US until 2024, then T+1; bond markets often still T+2; futures and FX have their own. **SLA "next business day"** appears in customer support contracts and is the loosest version of the same idea — usually inclusive of weekends if you opened the ticket on Sunday afternoon. **Statute of limitations** is the legal-system version with even more variation: counted in calendar days, business days, or court days depending on jurisdiction and case type. The unifying observation is that "day" looks simple until you write a contract about it.
