The days of the week
Seven days, one unbroken cycle: Monday through Sunday in the ISO 8601 order used across most of the world, or Sunday through Saturday on North American calendars. The table below gives each day's standard abbreviations, its ISO number and where its English name comes from.
| ISO number | Day | 3-letter | 2-letter | Named after |
|---|---|---|---|---|
| 1 | Monday | Mon | Mo | the Moon (Old English mōnandæg) |
| 2 | Tuesday | Tue | Tu | Tiw, Germanic god of war (equated with Mars) |
| 3 | Wednesday | Wed | We | Woden / Odin (equated with Mercury) |
| 4 | Thursday | Thu | Th | Thor, god of thunder (equated with Jupiter) |
| 5 | Friday | Fri | Fr | Frigg, goddess associated with Venus |
| 6 | Saturday | Sat | Sa | Saturn (Latin diēs Saturnī) |
| 7 | Sunday | Sun | Su | the Sun (Old English sunnandæg) |
Monday start or Sunday start?
The international standard ISO 8601 defines Monday as the first day of the week and numbers the days 1 (Monday) to 7 (Sunday) — the convention used for week numbers, most European calendars and most scheduling software. Calendars in the United States, Canada, Japan and several other countries traditionally print Sunday in the first column instead.
The distinction matters in practice for ISO week numbers, which always treat Monday as the start: the week containing the year's first Thursday is week 1. It also matters in code — JavaScript numbers Sunday as 0, while ISO numbers it as 7.
Weekends vary too: Saturday–Sunday is the most common pattern worldwide, while many countries in the Middle East and North Africa take Friday–Saturday. Cross-border scheduling should never assume the other side's weekend.
Frequently asked questions
What are the days of the week in order?
In ISO 8601 order: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday. Calendars in the United States, Canada, Japan and several other countries display the same seven days starting from Sunday instead, but the cycle itself is identical everywhere.
What is the first day of the week?
It depends on the convention. The international standard ISO 8601 defines Monday as day 1 and Sunday as day 7, and most of Europe, and most business and programming contexts, follow it. Calendars in the United States, Canada, Japan, Israel and much of the Middle East traditionally show Sunday (or Saturday) first. Neither is "wrong" — they are display conventions over the same cycle.
Why are there seven days in a week?
The seven-day cycle goes back to ancient Babylonia, where it tracked the roughly seven-day phases of the Moon and the seven visible "wandering" celestial bodies — the Sun, the Moon and the five planets known to the naked eye. The cycle spread through the Hellenistic world and the Roman Empire and has run uninterrupted for well over two thousand years.
How did the days get their names?
The Romans named the days after the Sun, Moon and five planets, themselves named after gods. English kept Saturday, Sunday and Monday from Saturn, the Sun and the Moon, and replaced the Roman gods with Germanic counterparts for the rest: Tiw for Mars, Woden for Mercury, Thor for Jupiter and Frigg for Venus. Romance languages such as Spanish and French still use the Roman names directly (lunes/lundi from the Moon, martes/mardi from Mars, and so on).
Which days are the weekend?
Saturday and Sunday in most of the world. Many countries in the Middle East and North Africa observe Friday–Saturday, and Israel observes Friday afternoon through Saturday. When scheduling across borders, confirm the local working week — our meeting planner lets you set per-participant working days.
What weekday number does ISO 8601 use?
ISO 8601 numbers the days 1 through 7 starting with Monday, so Monday = 1 and Sunday = 7. Note that many programming environments differ: JavaScript's Date.getDay() returns 0 for Sunday through 6 for Saturday, a common source of off-by-one bugs.