Appendix B — Datetime formatting patterns

The fmt_datetime() function supports two powerful systems for custom datetime formatting: CLDR datetime patterns and strptime format codes. This appendix provides a comprehensive reference for both.

B.1 CLDR datetime patterns

The CLDR (Common Locale Data Repository) datetime pattern system allows you to create highly customized, locale-aware datetime output. A pattern string consists of two types of elements:

Pattern fields: one or more repetitions of a specific pattern character (from the reserved sets A–Z and a–z). These fields are replaced with date and time data when formatting.

Literal text: any characters outside the reserved sets, including spaces and punctuation. Text between single vertical quotes (e.g., 'at') is output verbatim. Use two adjacent single quotes ('') to represent a literal single quote.

B.1.1 Pattern examples

The following examples use the datetime "2018-07-04T22:05:09.2358(America/Vancouver)":

Pattern	Output
“mm/dd/y”	05/04/2018
“EEEE, MMMM d, y”	Wednesday, July 4, 2018
“MMM d E”	Jul 4 Wed
“HH:mm”	22:05
“h:mm a”	10:05 PM
“EEEE, MMMM d, y ‘at’ h:mm a”	Wednesday, July 4, 2018 at 10:05 PM

B.2 Year patterns

B.2.1 Calendar year (y)

The calendar year is always numeric. The field length specifies the minimum number of digits, zero-padded as necessary. The exception is "yy", which yields only the two low-order digits.

Pattern	Output	Notes
“y”	2018	Full year
“yy”	18	Two-digit year
“yyy” to “yyyyyyyyy”	2018 to 000002018	Zero-padded to width

B.2.2 Week-based year (Y)

The year in week-based calendars, where year transitions occur on week boundaries. This may differ from calendar year "y" near year transitions. Used with pattern "w" for ISO 8601 week dates.

Pattern	Output	Notes
“Y”	2018	Full year
“YY”	18	Two-digit year
“YYY” to “YYYYYYYYY”	2018 to 000002018	Zero-padded to width

B.3 Quarter patterns

B.3.1 Quarter of year (Q and q)

Quarter names vary by width and context. The formatting form (Q) is used within complete date strings; the standalone form (q) is for independent use (e.g., calendar headers).

Pattern	Output	Notes
“Q” / “q”	3	Numeric, one digit
“QQ” / “qq”	03	Numeric, two digits (zero-padded)
“QQQ” / “qqq”	Q3	Abbreviated
“QQQQ” / “qqqq”	3rd quarter	Wide
“QQQQQ” / “qqqqq”	3	Narrow

B.4 Month patterns

B.4.1 Month (M and L)

Month names vary by width and context. The formatting form (M) is used within complete date strings; the standalone form (L) is for independent use.

Pattern	Output	Notes
“M” / “L”	7	Numeric, minimum digits
“MM” / “LL”	07	Numeric, two digits (zero-padded)
“MMM” / “LLL”	Jul	Abbreviated
“MMMM” / “LLLL”	July	Wide
“MMMMM” / “LLLLL”	J	Narrow

B.5 Week patterns

B.5.1 Week of year (w)

Values range from 1 to 53. Week 1 is the first week containing the minimum number of days specified for that locale.

Pattern	Output	Notes
“w”	27	Minimum digits
“ww”	27	Two digits (zero-padded)

B.5.2 Week of month (W)

Values range from 1 to 5. The first day of each month is always in week 1.

Pattern	Output
“W”	1

B.6 Day patterns

B.6.1 Day of month (d)

The day of the month, from 1 to 31.

Pattern	Output	Notes
“d”	4	Minimum digits
“dd”	04	Two digits (zero-padded)

B.6.2 Day of year (D)

Values range from 1 to 365 (or 366 in leap years). The field length specifies minimum digits with zero-padding.

Pattern	Output	Notes
“D”	185	Minimum digits
“DD”	185	Zero-padded to 2
“DDD”	185	Zero-padded to 3

B.6.3 Day of week in month (F)

Returns the occurrence number of the weekday within the month (e.g., “2nd Monday in March”). Days 1–7 yield 1, days 8–14 yield 2, and so on.

Pattern	Output
“F”	1

B.6.4 Modified Julian date (g)

The number of days since midnight November 17, 1858. Width specifies minimum digits with zero-padding.

Pattern	Output
“g” to “ggggggggg”	58303 to 000058303

B.7 Weekday patterns

B.7.1 Day of week name (E)

The name of the day of the week, available in four different widths.

Pattern	Output	Notes
“E”, “EE”, or “EEE”	Wed	Abbreviated
“EEEE”	Wednesday	Wide
“EEEEE”	W	Narrow
“EEEEEE”	We	Short

B.8 Period patterns

B.8.1 AM/PM (a)

Provides AM/PM and the narrow "a" and "p" forms.

Pattern	Output	Notes
“a”, “aa”, or “aaa”	PM	Abbreviated
“aaaa”	PM	Wide
“aaaaa”	p	Narrow

B.8.2 AM/PM with noon and midnight (b)

Provides AM/PM plus special forms for exactly noon (12:00) and midnight (00:00).

Pattern	At Midnight	At Noon	Notes
“b”, “bb”, or “bbb”	midnight	noon	Abbreviated
“bbbb”	midnight	noon	Wide
“bbbbb”	mi	n	Narrow

B.8.3 Flexible day periods (B)

Locale-specific phrases like “in the afternoon” or “in the evening”.

Pattern	Morning (08:30)	Afternoon (14:00)	Notes
“B”, “BB”, or “BBB”	in the morning	in the afternoon	Abbreviated
“BBBB”	in the morning	in the afternoon	Wide
“BBBBB”	in the morning	in the afternoon	Narrow

B.9 Hour, minute, and second patterns

B.9.1 Hour 0–23 (H)

Standard 24-hour clock where midnight is 00:00.

Pattern	Output	Notes
“H”	8	Minimum digits
“HH”	08	Two digits (zero-padded)

B.9.2 Hour 1–12 (h)

Standard 12-hour clock where midnight is 12:00.

Pattern	Output	Notes
“h”	8	Minimum digits
“hh”	08	Two digits (zero-padded)

B.9.3 Hour 1–24 (k)

Less common 24-hour clock where midnight is 24:00.

Pattern	Output	Notes
“k”	9	Minimum digits
“kk”	09	Two digits (zero-padded)

B.9.4 Hour 0–11 (K)

Less common 12-hour clock where midnight is 00:00.

Pattern	Output	Notes
“K”	7	Minimum digits
“KK”	07	Two digits (zero-padded)

B.9.5 Minute (m)

This is just the time part for the minute of the hour.

Pattern	Output	Notes
“m”	5	Minimum digits
“mm”	05	Two digits (zero-padded)

B.9.6 Second (s)

Provides solely the time part for the second of the minute.

Pattern	Output	Notes
“s”	9	Minimum digits
“ss”	09	Two digits (zero-padded)

B.9.7 Fractional second (S)

Truncates to the specified width. Add a decimal point manually to the pattern if needed.

Pattern	Output
“S” to “SSSSSSSSS”	2 to 235000000

B.9.8 Milliseconds in day (A)

The number of milliseconds since midnight (max 86,400,000).

Pattern	Output
“A” to “AAAAAAAAA”	439722 to 000439722

B.10 Era patterns

B.10.1 Era designator (G)

The Gregorian calendar has two eras: AD (Anno Domini) and BC (Before Christ).

Pattern	Output	Notes
“G”, “GG”, or “GGG”	AD	Abbreviated
“GGGG”	Anno Domini	Wide
“GGGGG”	A	Narrow

B.11 Time zone patterns

B.11.1 Specific non-location format (z)

User-friendly time zone names. Falls back to localized GMT format if unavailable.

Pattern	Output	Notes
“z”, “zz”, or “zzz”	PDT	Short specific
“zzzz”	Pacific Daylight Time	Long specific

B.11.2 Common UTC offset formats (Z)

ISO 8601 and localized GMT offset formats for time zones.

Pattern	Output	Notes
“Z”, “ZZ”, or “ZZZ”	-0700	ISO 8601 basic format
“ZZZZ”	GMT-7:00	Long localized GMT format
“ZZZZZ”	-07:00	ISO 8601 extended format

B.11.3 Localized GMT formats (O)

GMT-based offset formats that adapt to the user’s locale.

Pattern	Output	Notes
“O”	GMT-7	Short (omits zero minutes)
“OOOO”	GMT-07:00	Long (always includes minutes)

B.11.4 Generic non-location format (v)

Useful for recurring events where specific daylight/standard distinction isn’t needed.

Pattern	Output	Notes
“v”	PT	Short generic
“vvvv”	Pacific Time	Long generic

B.11.5 Time zone ID and exemplar city (V)

Formats that display time zone identifiers and representative cities.

Pattern	Output	Notes
“V”	cavan	Short time zone ID
“VV”	America/Vancouver	Long time zone ID
“VVV”	Vancouver	Exemplar city
“VVVV”	Vancouver Time	Generic location format

B.11.6 ISO 8601 formats with Z for UTC (X)

Uses Z when the local time offset is 0.

Pattern	Output	Notes
“X”	-07	Basic (h, optional m)
“XX”	-0700	Basic (h & m)
“XXX”	-07:00	Extended (h & m)
“XXXX”	-0700	Basic (h, m, optional s)
“XXXXX”	-07:00	Extended (h, m, optional s)

B.11.7 ISO 8601 formats without Z (x)

Same as X patterns but never uses Z for UTC.

Pattern	Output	Notes
“x”	-07	Basic (h, optional m)
“xx”	-0700	Basic (h & m)
“xxx”	-07:00	Extended (h & m)
“xxxx”	-0700	Basic (h, m, optional s)
“xxxxx”	-07:00	Extended (h, m, optional s)

B.12 strptime format codes

As an alternative to CLDR patterns, you can use strptime-style format codes. Each code starts with % and represents a specific date or time element.

B.12.1 strptime examples

The following examples use the datetime "2015-06-08 23:05:37.48":

Pattern	Output
“%m/%d/%Y”	06/08/2015
“%A, %B %e, %Y”	Monday, June 8, 2015
“%b %e %a”	Jun 8 Mon
“%H:%M”	23:05
“%I:%M %p”	11:05 pm
“%A, %B %e, %Y at %I:%M %p”	Monday, June 8, 2015 at 11:05 pm

B.12.2 Date codes

Format codes for year, month, day, and week components.

Code	Output	Description
“%a”	Mon	Abbreviated day of week
“%A”	Monday	Full day of week
“%w”	1	Day of week (0–6; Sunday = 0)
“%u”	1	Day of week (1–7; Monday = 1)
“%y”	15	Two-digit year
“%Y”	2015	Full year
“%b”	Jun	Abbreviated month
“%B”	June	Full month
“%m”	06	Month number (zero-padded)
“%d”	08	Day number (zero-padded)
“%e”	8	Day number (no padding)
“%j”	159	Day of year (zero-padded)
“%W”	23	Week number
“%V”	24	ISO 8601 week number
“%C”	20	Century number

B.12.3 Time codes

Format codes for hour, minute, second, and AM/PM components.

Code	Output	Description
“%H”	23	Hour (24-hour clock)
“%I”	11	Hour (12-hour clock)
“%M”	05	Minute
“%S”	37	Second
“%OS3”	37.480	Seconds with decimals (3 places shown)
“%p”	pm	AM/PM indicator

B.12.4 Other codes

Additional format codes for time zones and special characters.

Code	Output	Description
“%z”	+0000	Signed time zone offset
“%F”	2015-06-08	ISO 8601 date format
“%%”	%	Literal percent sign