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16 in-depth guides on Date Today and related topics.

Calendar facts

Calendar facts Julian vs Gregorian Calendar: Why the Dates Differ by 13 Days The Julian calendar is currently 13 days behind the Gregorian calendar. This article explains why the gap exists and where the Julian calendar is still used today. 4 min read Calendar facts How Often Is Friday the 13th? The Calendar Rules A month has a Friday the 13th if and only if it starts on a Sunday. Every Gregorian year has at least one and at most three. 3 min read Calendar facts Date Format By Country: Who Writes Dates Which Way The same six digits mean different days in London, New York and Tokyo. Here is the date format each country uses, and the two ways to write a date that cannot be misread. 5 min read Calendar facts Calendar Systems: Dates In Hijri, Hebrew And Chinese Years Today has a date in several calendars at once. Here is how the Hijri, Hebrew and Chinese systems are built, and why none of them keeps step with the Gregorian year. 6 min read Calendar facts Day Of Year And Julian Day Number Explained Every date has a plain ordinal number between 1 and 366. Here is how the day of year is calculated, how 29 February shifts it, and how it differs from a Julian day. 5 min read Calendar facts ISO Week Number Explained: The First-Thursday Rule Week numbers look simple until the turn of the year, when 1 January can land in week 52 of the year before. Here is the ISO 8601 rule that decides it. 5 min read Calendar facts Leap Year Explained: The Rule, The Reason, The Exceptions Divisible by four, except centuries, except centuries divisible by four hundred. Here is why that awkward rule exists, and what 29 February does to the rest of the year. 5 min read Calendar facts Week Start: Why Weeks Begin On Monday Or Sunday Two wall calendars can show the same month with the columns in different orders. Here is why the week start is disputed, who uses which, and what it changes. 5 min read

Quick answers

Quick answers Date Ordinals: 1st, 2nd, 3rd, 21st and the Teen Exceptions A practical guide to ordinal suffixes on dates, covering 1st, 2nd, 3rd, the 11th-13th exceptions, and when to leave them out. 4 min read Quick answers How Many Days Until Christmas? Count It Exactly Use the day-of-year method to count exactly how many days until Christmas, whether it's a common year or leap year. 3 min read Quick answers How Many Seconds, Minutes and Hours in a Day, Week and Year A complete reference for converting days, weeks and years into seconds, minutes and hours, including leap-year and average-year values. 4 min read Quick answers Is It Already Tomorrow Somewhere? How Many Dates Exist at Once Because of time zones, three different calendar dates can exist on Earth at the same moment. Here is how that works. 3 min read Quick answers Counting Business Days: What Counts And What Does Not A deadline quoted in business days is shorter than it looks. Here is what counts as a working day, how weekends and holidays come out, and why the answer changes by country. 5 min read Quick answers Days Between Two Dates: How To Count Them Correctly Counting the days between two dates is simple arithmetic that goes wrong constantly. Here are the inclusive and exclusive rules, and the boundaries that break manual counting. 6 min read Quick answers How Many Days Left In The Year? Work It Out Exactly The days left in the year is one subtraction away once you know the day of year. Here is the arithmetic, the leap year adjustment, and the inclusive-counting trap. 5 min read Quick answers What's The Date Today? How To Read And Write It Today's date can be written half a dozen ways, all correct. Here is how to read each one, why they differ, and what else the date tells you about the year. 6 min read