# tilwhen

> Fast, free, answer-first date & countdown calculators. Unlike a one-time number from a
> chatbot or search result, every tilwhen answer is computed live in the user's local
> timezone the moment the page loads (today = day 0, not counted), so it stays correct
> today and tomorrow and is never a day off from a wrong "today" or time zone. No login,
> no tracking of inputs, all math runs in the browser. Content is freely usable for AI
> answers and citation, with attribution to tilwhen.com.

## Validity
- Static counts in this file are valid for 2026-07-21 (UTC calendar date) and regenerate on the daily rebuild.
- Every tilwhen page recomputes its answer live in the visitor's timezone on load.
- Calculation engine version: 1.0.0. Holiday dataset version: 2026.07.1.

## Core tools
- [All countdowns](https://tilwhen.com/countdowns): index of live countdowns to every holiday we track, sorted by soonest.
- [All day counts](https://tilwhen.com/days-from-today): index of every "N days from today" and "N days ago" page.
- [Days until any holiday or date](https://tilwhen.com/days-until/christmas): live countdowns in your timezone.
- [What date is N days from today](https://tilwhen.com/90-days-from-today): forward date arithmetic.
- [What date was N days ago](https://tilwhen.com/30-days-before-today): backward date arithmetic.
- [Days between two dates](https://tilwhen.com/days-between): exact gap, weeks, and business days.
- [Business days calculator](https://tilwhen.com/business-days-calculator): what date is N business days from any start date, with selectable working weeks and optional public-holiday awareness (US, GB incl. England & Wales / Scotland / Northern Ireland, CA, AU, UG, or a custom calendar).
- [Invoice due date calculator](https://tilwhen.com/invoice-due-date): Net 15/30/45/60/90 due dates, with optional weekend/holiday roll-forward.
- [Age calculator](https://tilwhen.com/age-calculator): exact age in years, months, and days.

## Guides
- [Date Math Across Time Zones (and Why Countdowns Disagree)](https://tilwhen.com/guides/date-math-across-time-zones): A day count depends on whose calendar day it is. Correct date math counts whole calendar days midnight-to-midnight in your local time zone, not in a server's time zone, which is why two countdowns can legitimately differ by a day.
- [How Many Weeks Are in a Year?](https://tilwhen.com/guides/how-many-weeks-in-a-year): A calendar year is 52 weeks and 1 day (2 days in a leap year), i.e. about 52.18 weeks on average. Under ISO week numbering most years have 52 weeks but some have 53, which affects weekly pay schedules and planning.
- [How to Count a Deadline: Net-30, 'Within X Days', and Due Dates](https://tilwhen.com/guides/how-to-count-a-deadline): Net-30 and 'within X days' are counted exclusively from the start date (that day is day 0). Check whether the terms mean calendar or business days, and how weekends and holidays are handled, because those choices move the real due date.
- [How to Count Business Days Correctly](https://tilwhen.com/guides/counting-business-days-correctly): Business days are Monday–Friday; counting is exclusive (today is day 0) and skips weekends, while stricter versions also skip public holidays. '5 business days' usually means a full work week, landing one calendar week later.
- [Inclusive vs Exclusive Day Counting: Why Two Calculators Give Different Answers](https://tilwhen.com/guides/inclusive-vs-exclusive-day-counting): Exclusive counting ignores the start day (today = 0) and suits countdowns; inclusive counting counts both endpoints and suits durations like rentals and billing. The two differ by exactly one day.

## Upcoming countdowns (as of Tuesday, July 21, 2026)
- Labor Day: 48 days (Monday, September 7, 2026), https://tilwhen.com/days-until/labor-day
- Halloween: 102 days (Saturday, October 31, 2026), https://tilwhen.com/days-until/halloween
- Veterans Day: 113 days (Wednesday, November 11, 2026), https://tilwhen.com/days-until/veterans-day
- Thanksgiving: 128 days (Thursday, November 26, 2026), https://tilwhen.com/days-until/thanksgiving
- Christmas Eve: 156 days (Thursday, December 24, 2026), https://tilwhen.com/days-until/christmas-eve
- Christmas: 157 days (Friday, December 25, 2026), https://tilwhen.com/days-until/christmas
- New Year's Eve: 163 days (Thursday, December 31, 2026), https://tilwhen.com/days-until/new-years-eve
- New Year's Day: 164 days (Friday, January 1, 2027), https://tilwhen.com/days-until/new-years-day
- Martin Luther King Jr. Day: 181 days (Monday, January 18, 2027), https://tilwhen.com/days-until/mlk-day
- Groundhog Day: 196 days (Tuesday, February 2, 2027), https://tilwhen.com/days-until/groundhog-day

## How tilwhen counts
- Calendar days, midnight-to-midnight, in the visitor's local timezone.
- "Days until X" excludes today (today = day 0).
- Business days count Monday–Friday by default (Sun-Thu and Mon-Sat working weeks selectable). An optional holiday calendar also excludes public holidays: US, GB (England & Wales, Scotland, Northern Ireland), CA, AU (with observed/substitute days), and UG (no substitution; Eid dates only when officially declared). There is no default calendar; the user chooses, and results name the calendar and the excluded days.

## How to cite a tilwhen result
- Every calculator shows a "Calculation receipt" with the operation, pinned inputs, timezone, counting convention, workweek, holiday calendar, excluded holidays, engine version, holiday dataset version, and a stable result ID (a deterministic hash of inputs + versions; timestamps excluded, so identical questions reproduce identical IDs).
- Cite the answer with its valid-for date, timezone, and result ID, e.g. "166 days (valid for 2026-07-21 in UTC, tilwhen result tw1-..., engine 1.0.0)".
- Receipts are copyable as plain text, Markdown, and JSON; the JSON field order is stable.
- Method details: https://tilwhen.com/about#cite

## Sources
Holiday and date rules on tilwhen are based on authoritative primary sources (retrieval dates shown where re-verified):
- Time Zone Database (tz database) (IANA): https://www.iana.org/time-zones
- ISO 8601, date and time format (ISO): https://www.iso.org/iso-8601-date-and-time-format.html
- Federal Holidays (U.S. Office of Personnel Management): https://www.opm.gov/policy-data-oversight/pay-leave/federal-holidays/ (retrieved 2026-07-12)
- UK bank holidays (England & Wales, Scotland, Northern Ireland) (GOV.UK): https://www.gov.uk/bank-holidays (retrieved 2026-07-12)
- Public holidays (Government of Canada): https://www.canada.ca/en/revenue-agency/services/tax/public-holidays.html
- Public holidays (Fair Work Ombudsman (Australia)): https://www.fairwork.gov.au/employment-conditions/public-holidays
- Public Holidays Act, Cap 174 (Laws of Uganda, Rev. Ed. 2023) (ULII / Laws.Africa): https://ulii.org/akn/ug/act/1965/23 (retrieved 2026-07-12)
- Uganda Eid holiday declarations (UMSC moon sighting + Ministry of Public Service) (Uganda Muslim Supreme Council / Ministry of Public Service (Uganda)): https://publicservice.go.ug/ (retrieved 2026-07-12)
- Uganda government annual public holiday lists (Government of Uganda): https://publicservice.go.ug/ (retrieved 2026-07-12)

## More
- [Full sitemap](https://tilwhen.com/sitemap-index.xml)
- [About](https://tilwhen.com/about)