Calendar Calculator

Use the calendar calculator to add days to date and subtract days from a date. This time calculator works similarly to the date to date calculator and the day counter, but is specifically designed for time addition and time subtraction, instead of just counting the days between two dates.

This tool works in all sorts of different time units - years, months, weeks, and days, so not only can you answer questions like "what day will it be 90 days from today?" or "what date will it be 6 months from today?", but also add and subtract the sum of different time units (e.g. 2 years, 6 months, 3 weeks, and 2 days). You no longer need to stress about when your deadlines are.

In this article, we are going to present information on:

• How to use the calendar calculator;
• Add days to the date using the calendar calculator;
• The history of the Gregorian calendar;
• How to calculate the days until holidays in the calendar;
• What calendar do we use;
• What holidays are coming up; and
• What calendar has 13 months.

You are now free from the burden of forecasting the calendar days. Rejoice.

1. Input the start date - choose it from the calendar or type in the first three letters of the month's name followed by the day number, a comma, and the year (e.g. Oct 3, 2020).

2. In the next field, choose whether you want to add to or subtract time from the start date.

3. Input the number of years, months, weeks, and days you want to add or subtract.

4. The end date is the result of time addition or subtraction. If you click the calendar icon on the right of the date, you can check which day of the week it will be/was.

We are going to show how easy it is to calculate the days between dates using our calendar calculator. Let's say you want to know the date 90 days from today - this means you need to add days to the date. To do that:

1. Choose today as the start date (it will be highlighted in the calendar).

2. Leave the default "add" option in the second field.

3. In the "days" field, input "90." This is the number of days between the dates.

4. In the last field in the calendar days calculator, you'll find what date it will be 90 days from today.

Let's say you need to know which day was 6 weeks and 3 days ago, or in other words, 45 days ago. To check this with our calendar days calculator:

1. Choose today as the start date.

2. Choose "subtract" in the second field of the calendar calculator.

3. Input "6" in the "weeks" field.

4. Input "3" in the "days" field.

5. The result of your time subtraction is shown in the last field of the date calculator.

This subtraction means going back in time 45 days from today. So you could also input 45 days instead of 6 weeks and 3 days.

This time calculator is based on the Gregorian calendar. This means we assume:

• A year is 12 months long - that's because there are over 12 lunar cycles in a year, and calendars used to be based on the motion of the Moon and the Sun. The Moon phase calculator is definitely worth checking!

A year is 365.25 days long, which is an approximation of the time it takes Earth to complete a full orbit around the Sun.

• A week is 7 days long - this can't be explained in terms of natural phenomena. Historians suppose ancient Babylonians introduced a 7-day week. The reason remains unclear; one hypothesis says they attached some spiritual meaning to the number 7.

In this date calculator, the month's length is 30.44 - the average result of dividing the number of days in a year by the number of months in a year:

365.25 / 12 = 30.4375

30.4375 ≈ 30.44

The Gregorian calendar was introduced by Pope Gregory XIII in 1582, when a reform to the Julian calendar was established to realign the calendar with the seasons and the Council of Nicaea's formula for determining Easter. By doing it, the day October 4th,1582 was followed by October 15th, 1582.

The calendar also introduced a new algorithm to compute the leap years. It considers a leap year as a year divisible by four, and century years (those ending in "00") are leap years only if they are divisible by 400. Therefore, 2000 was a leap year, while 1800 and 1900 were not. This change in computing the leap years made the average calendar year 365.2425 days long, close to 365.2422 days of one "solar" year – determined by the Earth's revolution around the Sun. This means an amazing error reduction from 1 day in 128 years to 1 day in 3,030 years!

The Gregorian calendar has 12 months of 28–31 days. The year has 365 days, and one leap day is added to February every leap year.

One curiosity is that September ("seven") and December ("ten") kept their names even after changing their positions when July (for Julius) and August (for Augustus) were included. Nowadays, the Gregorian calendar is the most popular in the world and is used as a standard calendar in dating systems and our calendar calculator.

We've come a long way from the Big Bang to the calendar date calculator. Here are some crucial steps humanity has taken:

• Sexagesimal system - a numeral system with 60 as a base (as opposed to 2 in binary and 10 in the decimal system) developed by the ancient Sumerians. Although not a timekeeping device per se, the system is significant as it is still used for calculating time (e.g., 60 seconds make 1 minute), angles, and geographical coordinates. Interestingly enough, seconds are called such because they are the second division of an hour, after a minute.

Sundials—One of the earliest timekeeping devices, a sundial relies on the Sun. Cloudy days and nights impede its use.

• Water clock - Developed in ancient Egypt, a water clock consists of water flowing into a container with marked lines of measurement, which would inform you how much time had passed. In 4^th BC, the Greeks started using it and called it clepsydra ("water thief").

Candle clock—The earliest references to these date back to Ancient China. Melting wax with consistently spaced markings indicates the flow of time.

Hourglass - The principle of operation of the hourglass is very similar to that of the water clock, but instead of flowing water, there is sand.

• Pendulum clock - Christiaan Huygens (known for many discoveries including centrifugal force) built it based on the ideas and calculations of Galileo Galilei (the 16^th-17^th century polymath, pioneer at building telescopes, father of modern physics, and the guy who dropped balls from the Leaning Tower of Pisa, and didn't drop the ball).

• Pocket watch: Developed in 16^th century, it used a balance spring instead of a pendulum and was the most popular kind of watch before the invention of wristwatches.

• Wristwatch: Initially worn mainly by women, later it was used in the army (pulling out a watch from your pocket is not the most convenient thing to do in situations where you shoot and can be shot). They became popular after World War I, as people's perception changed to "wristwatches are a manly thing".

• Quartz watch - instead of a pendulum or a balance spring, it uses a tiny quartz crystal, which oscillates with a specific frequency when the electric current from a battery passes through it. See the simple harmonic motion calculator to learn more.

• Atomic clock - uses the oscillations of a cesium 133 atom. The international standard definition of a second is the duration of 9,192,631,770 periods of radiation produced by the transition between two levels of the cesium 133 atom. Which in practice means... super accurate clocks.