Two counts on one page
A calendar date and a weekday answer different questions. “The 15th” tells you where you are within a month. “Tuesday” names a place in the repeating seven-day week. A month can begin on any weekday.
After Sunday comes Monday even when the month changes. The weekday cycle carries on; it does not restart at the beginning of each month.
Try it yourself
Suppose today is Monday. To find the day three days later, move forward one day at a time:
- Tuesday: one day has passed.
- Wednesday: two days have passed.
- Thursday: three days have passed.
Do not count Monday as a day that has already passed. It is where you start.
Keep going and you reach Monday again after seven days. After eight days, it is Tuesday.
A month is not four weeks
Four weeks contain 28 days. A month can have 28, 29, 30 or 31 days. So a 30-day month lasts four weeks and two more days.
The calendar widely used today is called the Gregorian calendar. An ordinary year has 365 days. A leap year has 366, with the extra day added in February.
These extra days help keep calendar dates in step with the seasons.
Need an exact count? Check the dates
Two months do not always contain the same number of days. January has more days than February, and February itself is longer in a leap year.
If you need an exact number of days, check the dates on a calendar. Do not treat every month as thirty days.
Next, we can put years into groups of one hundred. Each of those groups is a century.