DateCalc
Quickly calculate date differences, future or past dates, and weekdays on one page.
Date Difference Calculator
Calculate the number of days from the start date to the end date.
Date After a Number of Days
Calculate the date after a specified number of days from the base date.
Date Before a Number of Days
Calculate the date before a specified number of days from the base date.
Weekday Calculator
Calculate the day of the week for the entered date.
About DateCalc
DateCalc is a free web tool that provides day difference calculations between two dates, date calculations for a certain number of days after or before a base date, and weekday checking for an entered date. It also supports including or excluding the start date, making it useful for anniversaries, schedule checks, contract date calculations, and D-day tracking. This calculator uses calendar-day calculations and does not currently provide business day, holiday, or workday calculations.
Accessibility-friendly use
Keyboard use and input error guidance
This date calculator is designed so you can use it without a mouse by moving through input fields, options, and calculation buttons in order with the Tab and Shift+Tab keys. If a date or day value is invalid, the input field and an error message are shown together so you can easily identify what needs to be corrected.
Checking results and assistive technology support
Calculation results are shown immediately in a separate result area, and that area is structured so assistive technologies can detect changes. This helps users of screen readers and other assistive tools check date differences, future dates, past dates, and weekday results more clearly.
Language and display settings
You can view the content in your preferred language through the language setting, and an easy-to-understand version is also available for clearer guidance. Text size and screen display settings are also supported, so users can choose the size and display mode that work best for them on both mobile and desktop.
How to use it and calculation rules
What you can do with this calculator
Use the date difference calculator to check how many total days are between two dates. Use the days-after calculator to find when an event will occur from a specific base date. Use the days-before calculator to check dates earlier than a base date, such as contract start dates, application deadlines, or preparation start dates. Use the weekday calculator to quickly see what day of the week a specific date falls on. All results are shown instantly on the same page.
Difference between including and excluding the start date
Exclude start date means the first day is not counted. Include start date means the first day is counted as day 1. For example, if the start date is April 15, 2026, then 1 day later is April 16, 2026 when excluding the start date, but April 15, 2026 when including it. For 100-day calculations, anniversary calculations, and D-day tracking, the result can differ depending on which rule you use, so it is best to decide first whether to include the start date.
Results are shown immediately based on the dates you enter. You can get more accurate results by checking the date format (YYYY-MM-DD) and whether the start date is included.
Examples of date calculations
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Calculate the number of days between two dates
From April 1, 2026 to April 15, 2026 is 14 days when excluding the start date, and 15 days when including the start date. -
Calculate the date 100 days later
If the base date is April 15, 2026, then 100 days later is July 24, 2026 when excluding the start date. -
Calculate the date 30 days earlier
If the base date is April 15, 2026, then 30 days earlier is March 16, 2026 when excluding the start date. -
Check the weekday of a specific date
For example, if you enter April 15, 2026, the result is Wednesday. The weekday calculator is useful for checking whether a date falls on a weekday or weekend. -
Check anniversaries and D-days
You can use it to check the remaining time until or the exact date of events such as anniversaries, contract expiration dates, exam dates, or trip departure dates.
Frequently Asked Questions
What features does DateCalc provide?
This date calculator provides day difference calculations between two dates, date calculations for a certain number of days after or before a given date, and weekday calculations for an entered date.
What is the difference between including and excluding the start date?
Excluding the start date means the starting day is not counted. Including the start date means the starting day is counted as day 1.
How do I calculate 100 days?
Enter the base date and number of days in the days-after calculator to check the date 100 days later. If needed, you can select the include start date option to match your preferred counting rule.
Can the difference between two dates be shown as a negative number?
Yes. If the end date is earlier than the start date, the result may be shown as a negative number of days. You can swap the date order to check it as a positive value.
What does the weekday calculator show?
It shows which day of the week the entered date falls on, from Sunday to Saturday.
Is DateCalc free to use?
Yes. DateCalc is a free single-page date calculation tool available on the web.
For D-day calculations, should I choose include start date or exclude start date?
In general, choose include start date if you count the starting day as day 1, and choose exclude start date if you start counting from the next day. It is important to decide on one rule first and use it consistently.
Can it calculate business days excluding weekends or holidays?
Currently, DateCalc provides calendar-day calculations. Calculations excluding weekends, holidays, or business days are not provided separately.
Are the dates or calculation records I enter stored?
The dates and day values you enter are processed only to display calculation results and are not stored as member data. Please check the privacy notice for more details.
Privacy notice
DateCalc processes the dates and day values entered by users only for the purpose of displaying calculation results and does not separately store or collect them as member data. It does not provide sign-up, login, comments, or inquiry submission features, so it does not directly collect personally identifiable information such as names, contact details, or email addresses. However, Google Analytics 4 (GA4) may be used to monitor service quality, and anonymous statistical information such as access environment, page views, and events may be processed during that process. If you do not want this, you can control tracking by restricting or deleting cookies in your browser settings.