Weekday Abbreviations: One-, Two-, and Three-Letter Codes Across Languages

Last reviewed on 2026-05-09

Open a weekly planner, a flight schedule, or a German bus timetable, and you'll quickly see that languages don't agree on how to abbreviate the days of the week. English diaries often use single letters — S M T W T F S. German timetables prefer two-letter forms — Mo Di Mi Do Fr Sa So. Software working with international dates uses three-letter forms in English (Mon, Tue, …) or numeric ISO codes. This page is a working reference for the abbreviations you're most likely to meet, why they look the way they do, and where they can trip you up.

Every weekday abbreviation at a glance

Here is the standard English abbreviation for each day of the week, in the three lengths you are actually likely to meet — plus the longer variants that still turn up in handwriting and older print.

Day	3-letter	2-letter	1-letter	Variants still in use
Monday	Mon	Mo	M	—
Tuesday	Tue	Tu	T	Tues, Tu
Wednesday	Wed	We	W	Weds
Thursday	Thu	Th	T (R in US timetables)	Thur, Thurs
Friday	Fri	Fr	F	—
Saturday	Sat	Sa	S	—
Sunday	Sun	Su	S	—

The abbreviation for Thursday is the one people look up most often, because it is the least predictable. The standard short form is Thu; Thur and Thurs are both accepted in ordinary writing, and US university course catalogues frequently use R so that a single letter can distinguish Thursday from Tuesday (T). Software locales and the ISO-derived lists below always use Thu.

The abbreviation for Wednesday is Wed — the d comes from the silent-d spelling Wednesday, not from the pronunciation “WENZ-day”, which is why Wen is never correct. Weds appears in British diaries but is not used by any standard locale.

Abbreviations keep the capital letter of the full day name in English: days of the week are proper nouns, so Mon and Thu are capitalised even mid-sentence. Most other languages lower-case both the name and its abbreviation — see the rules for capitalising days of the week for the language-by-language detail.

Reading SunMonTueWedThuFriSat and other run-together strings

Calendar widgets, spreadsheet headers and date-picker code often print the week as one unbroken string: SunMonTueWedThuFriSat, MonTueWedThuFriSatSun, or the terser SMTWTFS and MTWTFSS. They are not codes to decipher — they are simply the seven three-letter or one-letter abbreviations concatenated, and the only thing that changes between them is which day the week starts on.

SunMonTueWedThuFriSat — Sunday-first, the default in the United States, Canada and Japan.
MonTueWedThuFriSatSun — Monday-first, the ISO 8601 order used across most of Europe.
SMTWTFS — the same Sunday-first week reduced to initials; the two Ss are Sunday and Saturday, the two Ts Tuesday and Thursday.
M T W Th F — a five-day working week, with Thursday given two letters precisely to keep it apart from Tuesday.

If a string starts with S and ends with S, you are looking at a Sunday-first week. If it starts with M, it is Monday-first. Which one is “right” depends entirely on the country — we cover the split in detail in what the first day of the week is, country by country.

Why English single-letter codes fail and two-letter codes don't

If you write a row of single letters for the seven English weekdays, you get S M T W T F S — two pairs that collide. Sunday and Saturday both start with S; Tuesday and Thursday both start with T. The convention solves the ambiguity contextually: in a horizontal weekly planner, the first S is whichever day starts your week (Sunday in US-published planners, Monday-first planners drop the leading Sunday), and the second always means the other one. The same logic applies to T.

Two-letter codes resolve the collision: Su Mo Tu We Th Fr Sa. Three-letter codes resolve it again with redundancy: Sun Mon Tue Wed Thu Fri Sat. Most software libraries and spreadsheet locales standardise on the three-letter form because it is unambiguous, fits in narrow columns, and lines up across rows.

Side-by-side abbreviations across languages

Language	Mon	Tue	Wed	Thu	Fri	Sat	Sun
English (3-letter)	Mon	Tue	Wed	Thu	Fri	Sat	Sun
English (2-letter)	Mo	Tu	We	Th	Fr	Sa	Su
Spanish	lun	mar	mié	jue	vie	sáb	dom
French	lun	mar	mer	jeu	ven	sam	dim
Italian	lun	mar	mer	gio	ven	sab	dom
German (2-letter)	Mo	Di	Mi	Do	Fr	Sa	So
Dutch	ma	di	wo	do	vr	za	zo
Swedish	mån	tis	ons	tor	fre	lör	sön
Polish	pn	wt	śr	cz	pt	sob	nd
Russian	пн	вт	ср	чт	пт	сб	вс
Greek	Δευ	Τρι	Τετ	Πεμ	Παρ	Σαβ	Κυρ
Japanese (single char)	月	火	水	木	金	土	日
Chinese (single char)	一	二	三	四	五	六	日

For complete day names, pronunciations, and grammar notes, see the language hubs: Spanish, French, Italian, German, Dutch, Swedish, Polish, Russian, Greek, Japanese, and Chinese.

Patterns to notice

Three-letter Romance languages

Spanish, French, and Italian all use three-letter abbreviations that drop the suffix and keep the recognisable beginning of each name. Spanish keeps the accent on mié and sáb; French and Italian drop their accents in this short form. Software locales sometimes silently strip accents in tight column widths, so the displayed form may be mie or sab on some calendars.

Two-letter Germanic and Slavic languages

German has standardised on two letters because three-letter abbreviations would collide for several days that begin with the same syllable. Polish takes the same approach with even tighter abbreviations (pn for poniedziałek). Dutch follows the German pattern but in lower case. Russian uses two-letter Cyrillic codes that are common on calendars and timetables.

Single-character East Asian forms

Japanese and Mandarin both use a single character per day, but their underlying systems differ. Japanese uses element-based names — Moon, Fire, Water, Wood, Metal, Earth, Sun — and abbreviates each to its element character (月火水木金土日). Chinese uses a numbered system: xīngqī yī (week one = Monday) through xīngqī liù (week six = Saturday), with xīngqī rì or xīngqī tiān for Sunday. The single-character abbreviation is just the number — 一 for Monday, 二 for Tuesday, and so on. See numbered vs. named day systems for the broader pattern.

ISO codes for software

When you need an unambiguous numeric code rather than a letter abbreviation, ISO 8601 defines:

Monday = 1
Tuesday = 2
Wednesday = 3
Thursday = 4
Friday = 5
Saturday = 6
Sunday = 7

This is the convention returned by strftime's %u directive in C-derived languages and by the ISOWEEKDAY function in Excel and Google Sheets. Be careful: the older %w directive returns Sunday = 0 through Saturday = 6, and the original WEEKDAY function defaults to Sunday = 1 through Saturday = 7. A spreadsheet that mixes the two conventions in the same workbook is a frequent source of off-by-one calendar bugs.

A short checklist for picking an abbreviation

For a printed weekly planner. Pick the language's standard letter form (one letter for English with the SS/TT context, two letters for German/Dutch, three for Romance languages).
For a multilingual UI. Use locale-aware libraries — they already store the conventional abbreviation for each language and adjust accent handling automatically. Don't hardcode English abbreviations and translate them.
For a database column. Store the ISO numeric code (1 = Monday) rather than the abbreviation. Display layers can format it however the user's locale requires.
For a public timetable. Match the convention of the country you're publishing in. Travellers expect to see the local form.

Common pitfalls

A few mistakes show up repeatedly in published material:

Using English three-letter forms in a non-English calendar. A diary that says "Mon Tue Wed" in a Spanish-language product looks careless even when accurate, because Spanish readers expect lun mar mié.
Mixing two- and three-letter forms in the same column. Pick one width and stick with it.
Stripping accents. Accents change letter identity in many languages. Where they are part of the standard abbreviation (Spanish mié, sáb; Polish śr), keeping them is the correct choice unless your medium genuinely cannot render them.
Confusing ISO and locale week numbering. When abbreviations sit alongside week numbers, the same Tuesday in early January can fall in different week numbers depending on which system is in force. See first day of the week by country.