Methodology
Every number on DayMath comes from the same small set of rules. This page lists them, with the official sources behind the holiday dates.
What counts as a business day
A business day is a Monday, Tuesday, Wednesday, Thursday or Friday that is not a holiday in the selected holiday set. Saturdays and Sundays are never business days unless you change the weekend days under Advanced options. Dates you add as extra exclusions are skipped like holidays.
Holiday sets
The calculators offer four holiday sets. The default is US Federal.
| Set | Holidays | Saturday holiday | 2026 |
|---|---|---|---|
| US Federal | The 11 federal holidays in 5 U.S.C. 6103 | Observed Friday | 250 |
| Banks (Federal Reserve) | The same 11 holidays | Not moved; Reserve Banks open Friday | 251 |
| Stock market (NYSE) | New Year’s Day, Martin Luther King, Jr. Day, Washington’s Birthday, Good Friday, Memorial Day, Juneteenth, Independence Day, Labor Day, Thanksgiving, Christmas | Observed Friday, except New Year’s Day | 251 |
| None (weekends only) | No holidays; weekends only | — | 261 |
The 11 federal holidays are New Year’s Day (January 1), Birthday of Martin Luther King, Jr. (third Monday in January), Washington’s Birthday (third Monday in February), Memorial Day (last Monday in May), Juneteenth National Independence Day (June 19, from 2021), Independence Day (July 4), Labor Day (first Monday in September), Columbus Day (second Monday in October), Veterans Day (November 11), Thanksgiving Day (fourth Thursday in November) and Christmas Day (December 25). Names follow the Office of Personnel Management.
Observed dates
- Saturday → Friday, Sunday → Monday. For the federal set, a holiday on a Saturday is observed the Friday before and one on a Sunday the Monday after (5 U.S.C. 6103(b) and Executive Order 11582).
- New Year’s Day on a Saturday is observed on Friday, December 31 of the year before. New Year’s Day 2028 is observed on Friday, December 31, 2027, so it appears in the 2027 count.
- Federal Reserve: a Saturday holiday is not moved. Federal Reserve Banks are open the Friday before (the Board of Governors closes). A Sunday holiday moves to Monday. In 2026, Independence Day falls on Saturday, July 4, so Friday, July 3 is a business day for banks but not for federal offices.
- NYSE: follows Saturday → Friday and Sunday → Monday, except that a New Year’s Day on a Saturday is not observed at all; the market is open on Friday, December 31, 2027. Good Friday is a market holiday. Juneteenth has been a market holiday since 2022.
Counting conventions
- Between two dates: the start date is excluded and the end date is included. Monday, November 16 to Friday, November 20, 2026 is 4 business days. With “Count the start date” on, both ends count: 5, like Excel’s NETWORKDAYS.
- Adding and subtracting: the calculator steps one day at a time in the chosen direction and counts each business day it lands on, like Excel’s WORKDAY. The start date is never counted. Friday, November 13, 2026 plus one business day is Monday, November 16, 2026.
- Starting on a weekend or holiday: the count begins with the next business day in that direction. Saturday, November 7, 2026 plus one is Monday, November 9, 2026; minus one is Friday, November 6, 2026. Veterans Day, Wednesday, November 11, 2026, minus one is Tuesday, November 10, 2026.
- Countdowns count the days after today up to and including the target date, and also show the figure with today included.
One-off closures
Presidents sometimes close federal offices for an extra day by executive order, and markets close for national days of mourning. These closures are not in the default count, because they are announced at short notice and many businesses stay open. They are recorded only when an official source confirms them:
- Tuesday, December 24, 2024: Federal offices closed (Executive Order 14129). Federal Register
- Thursday, January 9, 2025: National Day of Mourning for President Jimmy Carter: federal offices closed (Executive Order 14133); NYSE markets closed. Federal Register · NYSE announcement
- Wednesday, December 24, 2025: Federal offices closed (Executive Order 14371). Federal Register
- Friday, December 26, 2025: Federal offices closed (Executive Order 14371). Federal Register
The NYSE closure on January 9, 2025 is part of the Stock market set. On each of these dates the Federal Reserve Board’s offices closed, but Reserve Bank payment services operated normally, so they are not in the Banks set.
Time zones and “today”
Dates are handled as plain calendar dates, so a time zone or a daylight-saving change can never shift an answer. The only time-zone question is what “today” is. Pages are built with today’s date in New York (Eastern Time), then your browser recalculates with your own time zone when the page loads. A visitor in Auckland and one in New York can see different answers on the same evening, and both are right for their own date.
Test it yourself
Today (Saturday, November 7, 2026) plus 10 business days is Monday, November 23, 2026. Try any date:
Result
Monday, November 23, 2026
10 business days after Saturday, November 7, 2026 · spans 16 calendar days · skips Veterans Day (Wed, Nov 11).
Sources
- U.S. Office of Personnel Management: Federal Holidays (2024–2030 checked)
- Federal Reserve Board: K.8 Holidays Observed by the Federal Reserve System (2026–2030 checked)
- NYSE: Holidays and Trading Hours (2026–2028 checked)
- Intercontinental Exchange: NYSE Group 2025–2027 holiday calendar and the 2024–2026 calendar
- Federal Register for executive orders closing federal offices
The holiday rules are written as code and tested against every date in these sources, plus 10,000 random checks against a simple day-by-day count.
How often it is updated
Pages are rebuilt every night so that answers based on “today” are current, and your browser refreshes them for your own date. The holiday lists are checked against the official sources once a year, when OPM, the Federal Reserve and the NYSE publish new calendars, and whenever a one-off closure is announced.
Limitations
- State, local and school holidays are not included. Add them as extra dates under Advanced options.
- Inauguration Day, a holiday only for federal employees in the Washington, DC area, is not included.
- Cut-off times are not modeled. Banks, carriers and agencies each set their own daily cut-offs, so a request made late in the day may start counting a day later.
- Dates from 2000 to 2099 are supported. One-off closures before 2024 are not recorded.
- Answers are for planning. For legal, financial or employment deadlines, confirm with the organization that sets the deadline.
Changelog
- November 7, 2026: first version of the date engine and holiday data (OPM 2024–2030, Federal Reserve 2026–2030, NYSE 2024–2028, four confirmed one-off closures). Subtracting from a weekend or holiday steps back to the previous business day (Saturday minus one is Friday).
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