Calendar Calculator
Use this calculator to easily add or subtract days to any date or to find the number of days between two days. It can also do calculations with calendar years, calendar months, and weeks. See what calendar date is in X days or was before a given number of days.
- Using the calendar calculator
- What date will it be in X days
- Days between calendar dates
- Examples of calendar time calculations
- Commonly used calendar intervals
Using the calendar calculator
There are two types of calendar time calculation that one often resorts to: adding time to a calendar date (or subtracting time), or determining the amount of time between two dates. In both cases the starting or initial date needs to be specified. Depending on the calculation type, additional information will need to be provided:
- to add or subtract calendar time: specify the number of calendar years, months, weeks, or the number of days to add or subtract
- to calculate time between calendar dates: specify the second date and whether to include the last day or not
The dates are automatically formatted based on your locale settings in your browser. When the time interval includes a leap year, the calculator takes that into account as well both when adding days, and when calculating the number of days between dates.
When calculating time between dates the output includes the number of days, and also the number of weeks, months, and years in between.
What date will it be in X days
One of the most common applications of a calendar calculator is to determine what date will be a certain number of days into the future. Questions like "What date will it be in 20 days?" can easily be answered by it.
To get the answer simply load the page in the "Starting date" field will show the current date in your preferred date format. Then, enter the number of days in the respective field and press "Calculate". For example, enter 10 in the "Days" field to see what date it will be after 10 days, or enter "2" in the "Months" field to see what date it will be in two months.
Days between calendar dates
The second most common calendar calculation is to determine the number of days between two dates. That number is easy to estimate by simple algebra if the calendar dates are within the same month, e.g. there are exactly 20 days between Dec 5 and Dec 25 since 25 - 5 = 20. However, things can get tricky when the time interval spans different months and especially years. With months the calculation needs to take into account that different calendar months have a different number of days in them - some have 30, some 31, and February can have 28 or 29 depending on whether it is a leap year or not. The leap year consideration also plays a role when going across years.
Examples of calendar time calculations
Example 1: If your doctor asks you to go for a check-up in 30 days, you might want to set a reminder. To estimate the calendar date for your check-up, first enter the current date, e.g. 20.05.2024 or May 20th, 2024. Then enter how many days you wish to add, in this case it is 30, and click "calculate" above. The calendar days adder will do the rest.
Example 2: You might want to check how many days have elapsed since you last checked the engine oil in your car motor. If the last check was on 10.01.2024 and today is 10.03.2024, then enter those calendar dates in the Starting date and End date fields, and press calculate. The answer is exactly 60 days between these dates, or two months, since 2024 is a leap year. Had these been the days of the same months but in 2025, the answer would have been 59 days since 2025 is a non-leap year.
Commonly used calendar intervals
Understanding calendar time units is important for accurate addition or subtraction to or from a calendar date. Converting all times, including the interval to add or subtract to seconds and then working with timestamps is often the preferred way of going about calendar math.
| Calendar time unit | Equals | In seconds |
|---|---|---|
| Year | 365 or 366 days* ~52 weeks |
~31,557,600 seconds |
| Month | ~4 weeks 28-31 days |
2,419,200 - 2,678,400 seconds |
| Week | 7 days 168 hours 10,080 min |
604,800 seconds |
| Day | 24 hours 1,440 min |
86,400 seconds |
* Approximately every four calendar years there is a "leap year" with 366 days due to February having one more day. 2020, 2024 and 2028 are such years. This also affects the number of hours, minutes, and seconds in a year.
** The second is the SI (The International System of Units) base unit. It can be written as sec or s. All other units are derivatives of it.
Cite this calculator & page
If you'd like to cite this online calculator resource and information as provided on the page, you can use the following citation:
Georgiev G.Z., "Calendar Calculator", [online] Available at: https://www.gigacalculator.com/calculators/calendar-calculator.php URL [Accessed Date: 29 Apr, 2024].