Date Calculator

This page holds two calculators. The first counts the years, months, weeks and days between two dates, and breaks that span into weekend days, holidays and business days. The second moves a date forward or backward by any number of years, months, weeks or days. Both draw the months involved as calendars with the dates picked out, so the answer can be checked against a page you already know how to read.

What the business-day count is doing

The workweek here runs Monday to Friday, with Saturday and Sunday as the weekend, in a seven-day week. Business days are the calendar days in the range with the weekends taken out, and then the holidays you have ticked taken out on top of that. A holiday only reduces the count when it lands on a workday, since a Saturday holiday was never a working day to begin with.

Fixed-date federal holidays are counted on the day they are observed rather than the day they fall. When Independence Day lands on a Saturday, as it does on Jul. 4, 2026, federal offices close on the Friday before. When it lands on a Sunday, as on Jul. 4, 2027, they close on the Monday after. Floating holidays such as Thanksgiving never need this, because they are defined as a particular weekday already.

The end date is not counted by default, which is the usual convention: from the 1st to the 8th is seven days, not eight. Tick "include end day" when the last day should count too, which is how notice periods and hire agreements are often written.

History of the Gregorian calendar

The Gregorian calendar is the most widely used calendar today. A standard year runs 365 days, with a leap day added to February in leap years. April, June, September and November have 30 days, February has 28 or 29, and the rest have 31.

It is a reformed version of the Julian calendar, which was itself a correction of the older Roman one. The earliest Roman calendar is thought to have been observational and lunar, following the phases of the moon. The Romans then used a ten-month calendar of 304 days, leaving roughly 50 days of winter unassigned to any month at all. Left alone, an arrangement like that lets the summer and winter months drift until they sit in the wrong season entirely, which is what pushed Rome toward something more accurate.

The Republican calendar that followed borrowed from Greek practice, assuming 29.5 days in a lunar cycle and 12.5 synodic months in a solar year, which line up every fourth year once the intercalary months of January and February are added. Repeated attempts were made to keep it in step with the solar year, including inserting an extra month into certain years. In 46 BC Julius Caesar reformed it again, replacing the dependence on observing the new moon with a fixed rule. He added ten days to the Republican calendar to bring the year to 365, and introduced a leap day every fourth year.

That still was not enough. The Julian year of 365.25 days is about 11 minutes longer than the solar year, and by 1582 the calendar had drifted ten days away from the equinoxes and solstices. Pope Gregory XIII dealt with the accumulated error by deleting those ten days outright, so the day after Oct. 4, 1582 was Oct. 15, 1582. He also changed which century years count as leap years: under the Gregorian rule a century year is only a leap year when it divides by 400. That is why 1600 and 2000 were leap years while 1700, 1800, 1900 and 2100 are not.

The correction is small and it matters. It gives a mean year of 365.2425 days rather than 365.25, cutting the error from roughly one day in 128 years to one day in 3,030. It also makes the Gregorian cycle exactly 146,097 days over 400 years, a number that divides by seven, so the whole pattern of dates and weekdays repeats every four centuries. Adoption took place slowly over the following centuries, country by country, and despite many proposals for further reform the Gregorian calendar is still the standard dating system worldwide.

Holidays

A holiday is a day set aside, by custom or by law, on which regular work or school is suspended or at least reduced. The word does not mean the same thing everywhere. In the United States paid leave is usually called vacation, and holiday is reserved for national, religious or cultural days off. In the United Kingdom and several former British colonies, holiday can mean paid leave as well.

Holidays generally mark an event, a person or a group of cultural or religious significance. Christmas and New Year's Day are observed widely across the world, but most countries keep their own set, and the same holiday can be observed differently from one place to the next: some bring a full stop to ordinary business, others only a partial day off. In Brazil, Carnaval closes down most of the country for the best part of a week, with only industrial production, retail and carnival-related businesses still running.

This calculator is built around US holidays, with anything else enterable by hand in the settings panel, and any holiday you do not observe can be unticked. Federal holidays in the US are the ones recognised by the federal government: federal offices close and federal employees receive paid leave. Private employers are not bound by that, and which federal holidays a private-sector worker gets is largely up to the company. Employees required to work a federal holiday are sometimes paid a premium on top of their usual wage.

Some holidays are fixed, in that they fall on the same date every year, as New Year's Day does. Others float. Martin Luther King Jr. Day is the third Monday in January, and Thanksgiving is the fourth Thursday in November, so their dates move from year to year. The two tables below show the federal holidays for 2026 and 2027 on the dates they fall.

2026 US federal holidays

New Year's Day	Jan. 1, 2026
Martin Luther King Jr. Day	Jan. 19, 2026
President's Day	Feb. 16, 2026
Memorial Day	May. 25, 2026
Juneteenth Day	Jun. 19, 2026
Independence Day	Jul. 4, 2026
Labor Day	Sep. 7, 2026
Columbus Day	Oct. 12, 2026
Veteran's Day	Nov. 11, 2026
Thanksgiving	Nov. 26, 2026
Christmas	Dec. 25, 2026

2027 US federal holidays

New Year's Day	Jan. 1, 2027
Martin Luther King Jr. Day	Jan. 18, 2027
President's Day	Feb. 15, 2027
Memorial Day	May. 31, 2027
Juneteenth Day	Jun. 19, 2027
Independence Day	Jul. 4, 2027
Labor Day	Sep. 6, 2027
Columbus Day	Oct. 11, 2027
Veteran's Day	Nov. 11, 2027
Thanksgiving	Nov. 25, 2027
Christmas	Dec. 25, 2027

Why the day count and the month count disagree

Months are not a fixed length, so a span can be described two ways and both be right. Aug. 13, 2020 to Aug. 13, 2026 is 6 years 0 months 0 days by calendar reckoning and 2,191 days by counting. Dividing 2,191 by 30 to get months would give 73, which is wrong, because six years of real months average slightly over 30 days each.

The same ambiguity shows up when adding. This calculator adds months by calendar and clamps the day of the month to the length of the month it lands in, so Jan. 31 plus one month is Feb. 28 in an ordinary year and Feb. 29 in a leap year. Adding 30 days instead would land on Mar. 2. Neither is wrong in the abstract; contracts usually mean the calendar version, which is why it is the default here.

Leap years, and the rule that catches people out

A year is a leap year when it divides by 4, unless it divides by 100, unless it also divides by 400. Most people remember the first part and forget the rest, which is how 1900 gets miscounted as a leap year. The rule adds 97 leap days every 400 years rather than 100, and those three missing days are the whole Gregorian correction.

The practical consequence is that any calculation spanning a century year needs the full rule. Software that only checked divisibility by 4 produced a well-known crop of bugs in 2000, which happened to be a leap year under both the wrong rule and the right one, so the mistakes stayed hidden until 2100 became the next real test.

Reading the results on this page

The panel leads with the total calendar days and then gives the same span three other ways: as years, months and days, as whole months plus days, and as whole weeks plus days. Underneath sit the three counts that split those days up, which always add back to the total: weekend days, holidays falling on a workday, and business days. Open the holiday list to see exactly which dates were removed, along with any that were shifted for observance. If you need the working day of the week for a single date, the day of the week calculator takes one date and answers that alone, and the age calculator applies the same calendar arithmetic to a birth date.