Date Calculator & Date Difference

6 October to 19 November is 44 days, or 45 days counting both ends

Enter Tuesday 6 October 2026 as the start date and Thursday 19 November as the end date and the answer is 44 days. That is 6 weeks and 2 days, or 1 month and 13 days by the calendar, and the span holds 32 weekdays (Mon–Fri) and 12 weekend days. Two of those weekdays are federal holidays, Columbus Day on 12 October and Veterans Day on 11 November, which leaves 30 business days. Turn on “Include end date” and 6 October itself counts as day 1, which makes it 45 days.

You can also work forward from a date. In “Add or subtract”, 100 days after 6 October is Thursday 14 January 2027, and 1 year 2 months 3 days after it is Thursday 9 December 2027. The sections below use worked numbers to explain why the two ways of counting differ by one day, why 31 January plus 1 month lands on 28 February, and how business days and legal periods differ.

A date difference and a span of days differ by one

There are two ways to count between two dates. The date difference is the end date minus the start date, so the start day itself is not counted. A span of days counts the first and last day alike, so it is one more than the difference. The days of a trip, a stretch of leave or a course of medication are usually counted as a span, while the days left to an exam or the gap between two events are counted as a difference. This calculator shows the difference by default and switches to the span when you turn on “Include end date”.

How the period between two dates is worked out

1. Both dates are reduced to midnight dates. Clock time is not used.
2. The start date is subtracted from the end date to get a whole number of days. From 6 October to 19 November that is the 25 days left in October plus 19 days of November, so 44 days. With “Include end date” on, 1 is added.
3. Weeks are the quotient and remainder of the day count divided by 7: 44 days is 6 weeks and 2 days.
4. For years, months and days, the tool adds years and then months to the start date by the calendar, takes the largest amount that does not pass the end date, and writes the leftover as days. Adding 1 month to 6 October gives 6 November, and 13 days remain to 19 November, so the answer is 1 month 13 days.
5. Weekdays are the Monday-to-Friday days counted from the day after the start date through the end date (from the start date itself when the end date is included). Of the 44 days, 32 are weekdays and 12 are weekend days. At this step public holidays still count as weekdays.
6. Business days are the weekdays minus the federal holidays that fall on a weekday. In this span Columbus Day (12 October) and Veterans Day (11 November) both fall on weekdays, so 32 − 2 = 30 business days.
7. If the start date is later than the end date, the two are swapped, the same calculation runs, and a note is added to the end of the sentence.

Adding and subtracting applies years and months first, then weeks and days

To add a period to a base date, the tool first adds years and months together in one step, then adds weeks and days. 1 year 2 months is added as 14 months, so the month-end adjustment never happens twice along the way. Subtraction is chosen under “Direction”, and the period boxes accept only whole numbers of 0 or more.

31 January plus 1 month is 28 February (month-end adjustment)

When the month you land in has no day with the same number, the result moves to that month's last day. Adding 1 month to 31 January gives 28 February because February has no 31st, or 29 February in a leap year. When this happens, a “Month-end adjustment” row under the result says which month lacked which day. Any weeks and days added afterwards continue from the adjusted date.

Counting in business days skips weekends and federal holidays

With “Count days as business days” on, the day count skips Saturdays, Sundays and US federal holidays. The holidays follow the federal holiday schedule published by the U.S. Office of Personnel Management (OPM), and the calculator has the dates for 2026 and 2027: New Year's Day, Martin Luther King Jr.'s Birthday, Washington's Birthday, Memorial Day, Juneteenth, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving Day and Christmas Day. In other years only Saturdays and Sundays are skipped, and the “Days skipped” row says so. In the date-difference mode the “Business days” row is filled in only when the whole period lies within 2026 and 2027. State holidays, extra days off granted later by executive order and company closures are not included.

A holiday that falls on a Saturday or Sunday is not subtracted twice. On OPM's schedule it is observed on a weekday instead (the Friday before a Saturday holiday, the Monday after a Sunday one), and that observed day is the one subtracted. Independence Day 2026 falls on Saturday 4 July, so the holiday counted here is Friday 3 July, and 4 July is simply a weekend day. New Year's Day 2028 is also a Saturday, so Friday 31 December 2027 is a holiday as well, which is why 2027 has 12 federal holidays on weekdays.

Adding business days follows the same rules. In “Add or subtract” with the option on, the day count passes over weekends and holidays, and the “Days skipped” row shows how many of each were passed. Adding 10 business days to Tuesday 6 October gives Wednesday 21 October, 15 calendar days later, because 4 weekend days and Columbus Day are skipped. Years, months and weeks are still added by the calendar whatever this option says.

Years, months and days are not “divide by 30”

Rough estimates such as “44 days is about a month and a half” treat every month as 30 days, which does not match the real calendar. This calculator adds months to the start date by the calendar, so the same “1 month” can be anywhere from 28 to 31 days. From 31 January to 1 March is 1 month (to 28 February) and 1 day, while from 31 January 2024 to 29 February 2024 is exactly 1 month. The rule is the same one used for adding dates, so adding the result back to the start date returns the end date.

Compared with Excel: subtraction, DATEDIF and NETWORKDAYS

Excel can give the same figures, but its functions do not agree on whether the start date counts, so results easily differ by a day. Microsoft describes NETWORKDAYS(start_date, end_date, holidays) (the holidays list is optional) as returning “the number of whole working days between start_date and end_date”, and its own example shows that both ends are counted: from Monday 1 October 2012 to Friday 1 March 2013 it returns 110, or 107 with three holidays listed. Counting the weekdays in that range with both dates included gives exactly 110, while leaving out the start date gives 109. To get the NETWORKDAYS figure here, turn on “Include end date”.

Microsoft warns that the "MD" argument of DATEDIF “may result in a negative number, a zero, or an inaccurate result” and does not recommend using it. For the days left over after whole months, counting from the start date plus those months to the end date, as the “Years, months, days” row does, avoids the problem. NETWORKDAYS without a holiday range skips only Saturdays and Sundays, so to match this calculator in Excel you need a list of the year's federal holidays (on their observed dates) as the third argument.

Different situations count differently

Legal periods: what matches this calculator and what does not

Contract terms, filing deadlines and court time limits follow rules written into each jurisdiction's law, and the details differ from place to place. Common patterns are that the first day is not counted so the count starts the next day, that periods in months or years follow the calendar, and that a deadline landing on a weekend or public holiday moves to the next working day.

This calculator's “Add” result gives the same date as counting from the day after the base date. “30 days from a notice on 6 October” starts on 7 October and ends on 5 November, and the calculator gives 6 October + 30 days = 5 November as well. Months usually work the same way: 1 month from 6 October is 6 November. The exception is a base date that is the last day of a month shorter than 31 days, such as 28 February or 30 April: rules that start counting on the next day then treat the period as whole calendar months and end it on the last day of the resulting month (31 March, 31 May), while this calculator gives 28 March or 30 May. What it also does not do is move a result that lands on a weekend or public holiday to the next working day, and it has no special rule for a period that starts at the very beginning of a day. Where a deadline is at stake, treat the result as a reference and confirm it against the governing statute and the authority's own guidance.

Leap years and 29 February

In the Gregorian calendar a year divisible by 4 is a leap year, except that years divisible by 100 are common years unless they are also divisible by 400. So 2024 and 2028 are leap years, while 2026 and 2100 are common years. Entering 29 February 2026 is rejected as a date that does not exist, while 29 February 2028 is accepted. The day count includes leap days as they fall, so 29 February 2024 to 29 February 2028 is 365 × 4 + 1 = 1,461 days.

Common mistakes

• Writing a span of days as a date difference. “For 45 days” and “44 days later” point to the same date. Stating which one a notice or contract uses avoids the confusion.
• Estimating a month as 30 days. From 1 February to 1 October 2026 is 8 months but 242 days, not 8 × 30 = 240.
• Adding months to a month-end date. 31 January plus 1 month is 28 February, and adding another month to that gives 28 March. Adding 2 months to 31 January in one step gives 31 March, a different result. This calculator adds years and months in one step.
• Subtracting a weekend holiday twice. Independence Day 2026 falls on Saturday 4 July, which is already a weekend day. Only the observed holiday, Friday 3 July, comes off the weekdays.
• Treating the one-day gap with NETWORKDAYS as an error. NETWORKDAYS counts the start date too. When the start date is a business day it gives one more than this calculator's default, and the two match once “Include end date” is on.
• Entering a negative number in the period box. Choose subtraction under “Direction”. The period boxes accept only whole numbers of 0 or more.

Limits and cautions

• Gregorian dates only. Convert a lunar date to a Gregorian date first, then enter it.
• Both the input and the result must fall between 1 January 1900 and 31 December 2100. Periods of up to 200 years, 2,400 months, 10,000 weeks or 73,000 days are accepted.
• Dates only: time of day and time zones are not used. For the time left to a moment, use the D-Day calculator.
• Holiday data covers 2026 and 2027 only. In other years only Saturdays and Sundays are skipped when adding business days, and the date difference shows no business-day count for a period that reaches outside those years. State holidays, days off granted later by executive order and company closures are not included.
• Calculations with rules of their own, such as legal or administrative deadlines, pregnancy weeks or age in completed years, are better handled by a dedicated calculator or the relevant authority's guidance.

Reference date The examples in this article are as of Tuesday 6 October 2026 (2026-10-06, Tue) and use the Gregorian calendar. Dates are written as YYYY-MM-DD following ISO 8601.

Sources

• 01U.S. Office of Personnel Management — Federal HolidaysFederal holiday dates for 2026 and 2027, including the observed weekday when a holiday falls on a weekend
• 02Microsoft Support — NETWORKDAYS functionSyntax and the 1 October 2012 to 1 March 2013 example (110, or 107 with three holidays)
• 03Microsoft Support — DATEDIF functionKnown issue with the "MD" argument (negative, zero or inaccurate results)
• 04U.S. Naval Observatory — Introduction to CalendarsPrimary explanation of the Gregorian leap-year rule (4, 100 and 400 years)
• 05W3C — Date and Time Formats (ISO 8601 profile)Basis for the YYYY-MM-DD notation used in this calculator and its share link

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