A calendar is the quickest way to answer questions such as “what day of the week is the 25th?”, “how many weeks are left in the month?” or “does February have 29 days this year?” This calendar shows any month from 1583 to 9999, highlights today, lets you choose whether weeks begin on Sunday or Monday, and reports the length of the month and the day of the year alongside the grid.
How to use the calendar
- Open on the current month. Today’s date is highlighted.
- Use the arrows to move one month at a time, or pick a month and type a year to jump anywhere.
- Choose the first day of the week. Sunday-first is common in the US; Monday-first is the ISO standard used in much of the world.
- Press Today to return to the current month.
Calendar formula: how a month is laid out
Rows = ⌈ (offset + days in month) ÷ 7 ⌉
Day of year = days from January 1 to the 1st of the month + 1
The weekday of the first of the month decides how many blank cells come before the 1st. Add the days in the month, divide by seven, round up, and you have the number of rows. A 28-day February that starts on the first day of the week fits into exactly four rows; a 31-day month starting on the sixth day of the week needs six.
Leap years
A year has 366 days when it is divisible by 4, unless it is a century year that is not divisible by 400. That is why 2000 and 2028 are leap years while 1900 and 2100 are not. The extra day is added to the end of February.
Example: October 2026
- October has 31 days. October 1, 2026 is a Thursday and day 274 of the year.
- With a Sunday-first week, the 1st sits in the fifth column, so the grid needs 5 rows.
- February 2028, a leap year, has 29 days and starts on a Tuesday.
2026 at a glance
| Month | Days | The 1st is a | Day of year of the 1st |
|---|---|---|---|
| January | 31 | Thursday | 1 |
| February | 28 | Sunday | 32 |
| March | 31 | Sunday | 60 |
| April | 30 | Wednesday | 91 |
| May | 31 | Friday | 121 |
| June | 30 | Monday | 152 |
| July | 31 | Wednesday | 182 |
| August | 31 | Saturday | 213 |
| September | 30 | Tuesday | 244 |
| October | 31 | Thursday | 274 |
| November | 30 | Sunday | 305 |
| December | 31 | Tuesday | 335 |
Calendar systems and numbering
This is a Gregorian calendar, the civil calendar in use in nearly every country. Week numbers differ by region: in the ISO system, weeks start on Monday and week 1 is the week containing the first Thursday of the year, while US convention often starts weeks on Sunday and counts week 1 as the week with January 1. If your workplace or school numbers weeks, check which rule applies.
- Need the number of days between two dates? Use the Date Calculator.
- Counting down to an event? The Days Until Calculator calculator does it from today.
- Planning in blocks of weeks? See the Weeks Calculator.
Frequently asked questions
How do I find the day of the week for any date?
Choose the month and year; the grid shows each date under its weekday. Check the “First day falls on” line to see the weekday of the 1st.
How do I tell whether a year is a leap year?
A year is a leap year if it is divisible by 4, except for century years, which must be divisible by 400. So 2028 and 2000 are leap years but 2100 is not.
Can I make the week start on Monday?
Yes. Use the “Week starts” menu to switch between Sunday-first (US style) and Monday-first (ISO and most of the world).
Why does the calendar start at 1583?
The Gregorian calendar was introduced in 1582 and adopted at different times by different countries. This calendar uses Gregorian rules throughout, so dates before 1583 would not match historical records.
What does day of the year mean?
It is the number of the day counted from January 1, which is day 1. December 31 is day 365, or 366 in a leap year. It is useful for scientific, military and ordinal date formats.