logo To Foot
© J R Stockton, ≥ 2013-01-28

Critical and Significant Dates.

No-Frame * Framed Index * Frame This
Links within this site :-

 Usage Counter Those benefiting from this site are invited to contribute to some local charity.

Conditions of Use and Citation

Please do not fetch this Web page (or others of mine) by automated subscription; that wastes my resources. Because of this abuse, I may sometimes change the name or offer only critdate.zip.


I do not permit the wording of this list of dates to be copied on the Net or elsewhere, either in whole or on part, except for "fair comment" extracts; but the dates and the facts are naturally public. By breaching my copyright, you implicitly agree to termination of your account.

I do not permit this Web page to be copied, except in these cases :-
  (i) as described in my Merlyn Home Page page,
  (ii) temporarily by agreement, for citation in print or equivalent (to reduce load on my own page at Demon),
  (iii) by normal transparent proxying/cacheing which serves a complete and substantially current version without any modifications overt or concealed,
  (iv) for personal private reference.

I may agree to limited copying within organisations. All copies must be headed with a proper attribution, must cite it as <URL:http://www.merlyn.demon.co.uk/critdate.htm>, and must give the date made.

Material on this page has neither been copied nor derived from Warren, McVeigh & Griffin, Inc..


Normal Web links to and citations of this page are welcome (there is no need to ask).

Those intending citation in popular print or broadcast media are requested to consult me first about cacheing or mirroring, and about relative links.

Critical Dates

The major criticalities are, sequentially, the August 1999 GPS rollover, the Year 2000 and all its two-digit rollover consequences, the Leapness of 2000 (including Day 366), and the 32-bit UNIX (and C library) Year 2038 problem; and also the various dates relating to introduction of the Euro currency.

There are or have been other critical date lists at Cinderella "Timeline", at Volker Kolberg's site, in Capers Jones's "Dangerous Dates" page, etc., etc. My more general Year 2000 and Date/Time references are now on other pages. Excerpts on Computer Calendar-Clock Problems by Peter G. Neumann (2000) is instructive. Some errors are described in Software Horror Stories by Nachum Dershowitz, with links.

Much of the following was picked up from the comp Y2k, UK Y2k and Risks (Risks Digest) Usenet newsgroups and from a Y2k FAQ, with the aid of the Calendar FAQ; also doncio and other Web pages such as at Mitre.

See also Wikipedia Time formatting and storage bugs, Notable epoch dates in computing.

See also, at IET, Dates Potentially Causing Problems in Computer Systems from 2001-2100 (discovered in 2011).

When I receive E-mail information correcting or extending the list, I will assume permission to quote.

Links like _ are not intended for general use.

The List of Dates

This is, fundamentally, a list of Critical and Significant Dates, which is not quite the same thing as a list of dates which ought to be used in testing; for example, 2000-02-29 was critical as possibly unexpected, but in testing one should also try 2000-02-28, 2000-02-30, 2000-02-31, 2000-03-00 & 2000-03-01, in order to make sure that the valid dates are consecutive and without overlap (Note 19); likewise for 2000-366. Some of the dates are those resulting from other date failures.

Some are important; some are possibly just amusing - it is up to you to discriminate.

This List is not a prediction of disaster; it is an indication of when error may be prevented by sufficient care.

Software errors may have been fixed in later versions.

The Gregorian calendar, with Historical year numbering, is to be assumed where necessary (some dates are UNCHECKED - you MUST verify - they may be a day or two out). However, many of the critical dates would be the same dates (which currently occur thirteen days later) in a consistently Julian environment. Note that, in computing, conventional day-numbers preceding 1900-03-01 and day-counts spanning 1900-02-28 to 1900-03-01 might be a day out, if a day in between those dates was assumed.

The more Critical Dates may have been chosen as trigger dates by virus writers - 2000-01-01, 2000-02-29, 2001.02.29, etc. - and may emulate date errors.

Some dates of non-computer origin are included. Historical dates are mainly limited to those of significance to UK history and culture.

For near-present Space dates, see Ron Baalke.

Virus trigger dates are NOT included - use a virus checker such as F-Prot (see PC Links Reference) and others.

Abbreviations should be obvious enough to those for whom they are significant.

2006-08-01 - New Warning

In general, I have mainly considered events relating to counting UP to particular numbers. There are also events relating counting DOWN; and those are less well predicted.

See 2006-05-13 and 2008-01-19 below as examples.

The Dates Themselves

Date Formats

To simplify use of my DoW checker :-
• Julian dates are given as YYYY/MM/DD.
• Only Gregorian AD dates are ISO 8601 hyphen-separated, unless invalid, when dots are used : otherwise, spaces are used.

Timing of Events

Some of these are local date/times; some are GMT/UTC or similar. I use GMT for legal GMT, with date changing at London mean solar midnight; the term UT might be confused with UTC.

It is very important to remember that the local time corresponding to a given GMT depends on the local Time Zone, and on Daylight saving; also that the time in question will be the time that the system is actually set to, not what it should be set to.

For example, a DOS/Windows PC will with high probability be set to local time internally, but a UNIX computer should be on GMT/UTC internally. DOS software translated from UNIX may default to California time settings.

Leap seconds may affect some dates, e.g. GPS rollover 1999, UNIX 2038.

The form a^b is used for "a to the power b" = ab. The form mEe is used for m×10e.

N.B. Two aspects of the year before AD 0001 are presented below, as BC 0001 and as ±0000 Astronomical.