About Days Until
A small, fast, single-purpose date calculator built around one idea: date arithmetic is easy to get subtly wrong, so a tool should show its working.
Why this site exists
Almost every "days between dates" tool on the web gives you a single number and moves on. That number is right about half the time, because the question is ambiguous: whether the end date counts changes the answer by one, and one day is exactly the size of error that causes missed deadlines, overstayed visas and disputed invoices. Days Until always shows both counts, tells you which convention each is for, and states the rule it uses for months instead of leaving you to reverse-engineer it.
The second half of the site is a set of countdown pages for the dates people ask about most. Those were built to solve a different problem: the countdown pages you find in search results are frequently stale. They were written for one particular year, and the day after that date passes they either freeze or start counting backwards.
How it is built
Plain HTML, one small stylesheet and a few kilobytes of vanilla JavaScript. No framework, no build step, no web fonts. The countdowns need nothing from the network: once a page has loaded it will keep working with the connection cut, and every calculation happens on your own device.
Three deliberate engineering choices are worth calling out:
- Calendar arithmetic, not millisecond arithmetic. Dates are reduced to a year–month–day triple before differencing, so daylight-saving transitions cannot produce a fractional or off-by-one day.
- Rules, not hardcoded dates. Recurring events are stored as a rule and resolved at page load. Thanksgiving is "the fourth Thursday of November"; Black Friday is the day after it; Easter is the full anonymous Gregorian computus. Nothing needs editing in December, or ever.
- Countdowns that cannot go negative. When the target day arrives, the display switches to an "it is here today" state and, at the following midnight, rolls forward to the next occurrence on its own — even in a tab that has been open for days. Year-specific pages instead say plainly that the date has passed and link to the evergreen equivalent.
Accuracy and corrections
The date logic is covered by a test suite that checks known values across several time zones, including zones with half-hour daylight-saving shifts: known Easter dates over several centuries, Thanksgiving across leap and non-leap years, ranges spanning both daylight-saving transitions, month-end clamping, and a sweep that verifies the countdown never runs backwards or shows a negative value.
That said, calendars are full of edge cases and conventions differ by jurisdiction. If a number here looks wrong, please tell us with the two dates and what you expected — that is the fastest way to get it fixed, and reproducible reports are always welcome.
What this site is not
It is not a legal, immigration, tax, payroll or medical tool, and it does not know the rules that govern your particular deadline. It does not know your country's public holidays. It gives you correct, clearly-labelled arithmetic; deciding which arithmetic applies to your situation is your call, and for anything consequential it is worth confirming with the body that set the deadline.
Cost and advertising
The site is free to use. Hosting is paid for by advertising, which may be introduced on these pages. No advertising or analytics code is present at the time of writing. The privacy policy explains what would change.