Introduction
The Add Days Calculator helps you find a future or past date by adding or subtracting days, weeks, months, or years from any start date. Need to know what date falls 30 days from today? Want to count 90 days back from a deadline? This tool calculates the new date for you.
You can also switch to business days mode, which skips weekends and US holidays. This is helpful for work deadlines, legal due dates, shipping estimates, and contract timelines. Just pick your start date, enter how many days to add or subtract, and hit calculate. The result shows the exact date, the day of the week, and a full breakdown of the time span.
How to Use Our Add Days Calculator
Enter a start date and a duration to find out what date falls before or after it. The calculator will show you the exact result date, the day of the week, and a full breakdown of the time span.
Start Date: Pick the date you want to count from. Today's date is filled in by default, but you can change it to any date you need.
Operation: Choose Add (+) to move forward in time or Subtract (−) to move backward in time from your start date.
Years, Months, Weeks, and Days: Type how much time you want to add or subtract. You can fill in one field or use several at once. For example, you could enter 1 year, 2 months, and 15 days all together.
Quick Presets: Click a preset button like 7 Days, 30 Days, 90 Days, or 1 Year to fill in the duration instantly without typing.
Business Days Mode: Check this box if you only want to count workdays and skip weekends. When this mode is on, you can only use the Weeks and Days fields.
Skip Weekends and Holidays: Inside Business Days Mode, choose whether to skip weekends only or skip both weekends and selected US holidays. You can check or uncheck each holiday and even add your own custom holidays by name and date.
Calculate Date: Press this button to see your result. The output shows the final date, the day of the week, a written summary, and a chart that breaks down the duration. Press Reset to clear everything and start over.
What Is Adding Days to a Date?
Adding days to a date means picking a starting date and counting forward by a set number of days to find a future date. For example, if today is March 1 and you add 10 days, the result is March 11. You can also subtract days to find a past date with our Days Ago Calculator. This process is sometimes called date arithmetic or date calculation.
Why Would You Need to Add Days to a Date?
People add or subtract days from dates all the time in everyday life. Here are some common reasons:
- Due dates: A bill or assignment might be due 30 days, 60 days, or 90 days from today.
- Shipping and delivery: A package might arrive 5 to 7 business days after you order it.
- Legal deadlines: Courts and contracts often set deadlines a certain number of days from a filing date.
- Project planning: Teams need to know when a task will finish if it takes a set number of days.
- Personal events: You might want to count how many days until a birthday, vacation, or anniversary with our Days Until Calculator.
Calendar Days vs. Business Days
Calendar days means every single day on the calendar, including weekends and holidays. If you add 10 calendar days, you count Saturday, Sunday, and every other day in between.
Business days means only the days when most people work, Monday through Friday. Weekends are skipped. Some calculations also skip public holidays like Thanksgiving, Christmas, or Independence Day. Business day counting is common for banking, shipping, and legal deadlines.
How Months and Years Work in Date Math
Adding months or years to a date is not the same as adding a fixed number of days. That is because months have different lengths. January has 31 days, February has 28 or 29, and April has 30. When you add 1 month to January 31, the result is February 28 (or February 29 in a leap year). This is called end-of-month clamping, and it keeps the result on a real, valid date.
What Is a Leap Year?
A leap year happens every 4 years. In a leap year, February has 29 days instead of 28. This extra day keeps our calendar lined up with the Earth's orbit around the Sun. A year is a leap year if it is divisible by 4, except for years divisible by 100. Those years count only if they are also divisible by 400. So the year 2000 was a leap year, but 1900 was not.