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| * The date format chosen by the first major contributor in the early stages of an article should continue to be used, unless there is reason to change it based on strong national ties to the topic or consensus on the article's talk page. | | * The date format chosen by the first major contributor in the early stages of an article should continue to be used, unless there is reason to change it based on strong national ties to the topic or consensus on the article's talk page. |
| * Where an article has shown no clear sign of which format is used, the first person to insert a date is equivalent to "the first major contributor". | | * Where an article has shown no clear sign of which format is used, the first person to insert a date is equivalent to "the first major contributor". |
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| ====<span id="Year numbering systems"></span><span id="Eras and other very long periods"></span>Era style====
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| {{shortcut|MOS:ERA|MOS:BCE}}
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| * The default [[calendar era]] is the [[Dionysian era|Western Dionysian era system]], a year numbering system also known as the Western Christian era (represented by {{xt|[[Anno Domini|BC and AD]]}}), or the [[Common Era]] (represented by {{xt|[[Common Era|BCE and CE]]}}).
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| ** {{xtn|BC}} and {{xtn|AD}} are the traditional ways of designating eras. {{xtn|BCE}} and {{xtn|CE}} are common in some scholarly texts and in certain topic areas. Either convention may be appropriate for use in Wikipedia articles.
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| *** Do not change the established era style in an article unless there are reasons specific to its content. Seek consensus on the talk page {{em|before}} making the change. Open the discussion under a subhead that uses the word "era". Briefly state why the style is inappropriate for the article in question. A personal or categorical preference for one era style over the other is not justification for making a change.
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| *** {{xtn|BCE}} and {{xtn|CE}} or {{xtn|BC}} and {{xtn|AD}} are written in upper case, unspaced, without a period (full point, <code>.</code>), and separated from the numeric year by a space ({{xt|5{{nbsp}}BC}}, not {{!xt|5BC}}). It is advisable to use a [[Wikipedia:Manual of Style#Non-breaking spaces|non-breaking space]].
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| *** {{xtn|AD}} may appear before or after a year ({{xt|AD{{nbsp}}106}}, {{xt|106{{nbsp}}AD}}); the other abbreviations appear only after ({{xt|106{{nbsp}}CE}}, {{xt|3700{{nbsp}}BCE}}, {{xt|3700{{nbsp}}BC}}).
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| *** In general, do not use {{xtn|CE}} or {{xtn|AD}} unless required to avoid ambiguity (e.g. {{xt|The Norman Conquest took place in 1066}} not {{!xt|1066{{nbsp}}CE}} nor {{!xt|AD{{nbsp}}1066}}) or awkwardness {{nobr|({{xt|January 1, 1 AD}} }} not {{nobr|{{!xt|January 1, 1}}).}} On the other hand, {{xt|[[Plotinus]] lived at the end of the 3rd century AD}} will avoid confusion. Also, in {{xt|He did not become king until 55{{nbsp}}CE}} the era marker makes it clear that ''55'' does not refer to the person's age (or write {{xt|He did not become king until the year 55}}). If the era is shown for the initial date in a range, then use it for the final date as well: not {{nobr|{{!xt|from 450 BCE to 200}}}} but {{nobr|{{xt|from 450 to 200 BCE}}}} or {{nobr|{{xt|from 450 BCE to 200 BCE}}}} (and definitely {{nobr|{{xt|from 100 BCE to 200 CE}}}}). {{See below|Ranges}}
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| *** Use either the BC{{ndash}}AD or the BCE{{ndash}}CE notation consistently within the same article. Exception: do not change [[MOS:QUOTE|direct quotations]], titles, etc.
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| * '''Uncalibrated (bce) radiocarbon dates:''' [[Calibrated years|Calibrated and uncalibrated]] dates can diverge widely, and some sources distinguish the two only via {{xtn|BCE}} or {{xtn|BC}} (for calibrated dates) versus {{xt|bce}}, {{xtn|bc}} or {{xtn|b.c.}} (uncalibrated). Avoid giving uncalibrated dates except in direct quotations, and even then a footnote or square-bracketed note [like this] should note that the date is uncalibrated or (ideally) give the calibrated date.
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| * '''BP or YBP''': In scientific and academic contexts, BP (before present) or YBP (years before present) are often used. (''Present'' in this context conventionally refers to January{{nbsp}}1, 1950.) Write {{xt|3000 years{{nbsp}}BP}} or {{xt|3000{{nbsp}}YBP}} or {{xt|3000{{nbsp}}years before present}} but not forms such as {{!xt|3000 before present}} and {{!xt|3000 years before the present}}. If one of the abbreviated forms is used, link to ''[[Before present]]'' on first use: {{xt|The Jones artifact was dated to 4000{{nbsp}}[[before present|YBP]], the Smith artifact to 5000 YBP.}}
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| * {{anchor|Other_era_systems}}'''Other era systems''' may be appropriate in an article. In such cases, dates should be followed by a conversion to Dionysian (or vice versa) and the first instance should be linked: {{xt|Qasr-al-Khalifa was built in {{nobr|221{{nbsp}}[[Hijri year|AH]] (836{{nbsp}}CE)}}}}, or {{nobr|{{xt|in 836{{nbsp}}AD (221{{nbsp}}[[Hijri year|AH]])}}}}.
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| ** [[Astronomical year numbering]] follows the Common Era and does not require conversion, but the first instance of a non-positive year should still be linked: {{xt|The March equinox passed into Pisces in [[Astronomical year numbering|year{{nbsp}}−67]].}}
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| ====Julian and Gregorian calendars==== | | ====Julian and Gregorian calendars==== |
