Calendar
A monthly calendar with week numbers, holidays and space for your own notes.
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Select any day for details. Use PageUp and PageDown to change month.
How it works
The grid is generated in your browser from date arithmetic alone. There is no stored table of months, which is why any month of any year renders instantly, including years far outside the range a spreadsheet will accept.
You choose whether weeks begin on Monday or Sunday and whether ISO 8601 week numbers appear down the side. The two are independent settings, but note that ISO week numbers are defined in terms of Monday-start weeks, so reading them against a Sunday-start grid needs care — the numbered week and the visible row no longer cover the same seven days.
Week 1 under ISO 8601 is the week containing the first Thursday of the year, which is why the first row of January sometimes begins in late December. That looks wrong at a glance and is correct.
Dates before 1582 are rendered by projecting Gregorian rules backwards — the proleptic Gregorian calendar. It is arithmetically consistent for any year and does not match what contemporaries wrote, since most of Europe was still on the Julian calendar and by then ten days adrift.
Examples
Checking a date falls where you think. Jump to any month to confirm a weekday before committing to it in an invitation.
Planning around week numbers. Switch week numbers on to line a schedule up with a project plan that is tracked by ISO week rather than by date.
Printing a month. The print stylesheet drops the navigation, search and footer, so what comes out is the grid rather than a screenshot of a web page.
Practical notes
Whether the week starts on Monday or Sunday is a regional convention, not a standard. ISO 8601 and most of Europe start on Monday; the United States, Canada, Japan and much of Latin America start on Sunday. If you are sharing a schedule internationally, say which you mean rather than assuming.
ISO week numbers are defined against Monday-start weeks. Displaying them beside a Sunday-start grid is possible but reads awkwardly, because the numbered week and the visible row no longer cover the same seven days.
Everything here is the proleptic Gregorian calendar, projected backwards without limit. It is internally consistent for any year, and for dates before 1582 it does not match what was written at the time — most of Europe was still using the Julian calendar and by then ten days adrift.
Frequently asked questions
Can I print the calendar?
Yes. The print button opens your browser’s print dialog with a layout that drops the navigation, buttons and ads.
Are my notes private?
They never leave your browser. Clearing site data removes them, so export anything you want to keep.
Why do the holidays not match my region exactly?
The bundled lists cover national holidays. State, provincial and religious observances vary widely — always confirm against an official source before relying on a date.
Can I start the week on Sunday?
Yes, and the choice is remembered on this device and shared with the other calendar tools.
Are dates before 1582 correct?
Arithmetically yes, historically no. They project modern rules backwards, which differs from the Julian dates recorded at the time — ten days by 1582, and more the further back you go.
Can I print a single month?
Yes. Printing drops the navigation and footer and lays out the visible month cleanly.
Does it show public holidays?
Not directly — holidays vary by country and region, so the holidays tool handles them separately.
Which years can I view?
Any year from 1 to 9999, though dates before 1582 use Gregorian rules projected backwards.
Can I jump to a specific month?
Yes, enter the month and year directly rather than paging through.
Why do some months start on a different day each year?
Because a common year is 365 days, which is 52 weeks plus one. Each date therefore shifts forward one weekday per year, or two across a leap year.
Why does the calendar start on Monday by default?
Because ISO 8601 defines the week that way and most of Europe follows it. If you prefer Sunday, change the setting; it is remembered on this device and shared across the calendar tools.
Guides on this topic
- How ISO week numbers work The rule that decides week 1, why some years have 53 weeks, why 29 December can fall in next year’s week 1, and how ISO weeks differ from the US system and Excel.
- Leap years, and why 2100 will not be one Why February gets a 29th day, the divisible-by-4 rule and its two exceptions, why 1900 was not a leap year but 2000 was, and how the Gregorian reform happened.