Calendar Calculator
Add or subtract days, weeks, months, and years from any date. Find the day of week, week number, and calculate the exact duration between dates.
Add or Subtract Time from a Date
Days Between Two Dates
Date Details
Quarter Information
Days Until Major U.S. Holidays (2026-2027)
Planning ahead? Here's a quick reference showing how many days remain until major U.S. holidays from today's date.
| Holiday | Date | Days Until |
|---|
How Date Calculations Work
Calendar calculations involve adding or subtracting time units from a starting date. While days and weeks follow simple arithmetic (7 days per week), months and years require special handling because months have varying lengths (28-31 days) and years may be leap years (366 days) or regular years (365 days).
When you add 1 month to January 31st, for instance, the result depends on whether it's a leap year. February only has 28 or 29 days, so the calculator adjusts to February 28th or 29th. This month-end adjustment ensures accurate results for any starting date.
Week Number Calculation (ISO 8601 Standard)
Week numbers follow the ISO 8601 international standard used in business and project management. Week 1 is the week containing the first Thursday of the year, which means January 4th is always in Week 1. Weeks start on Monday in this system, giving 52 or 53 weeks per year.
Leap Year Rules in the Gregorian Calendar
A year is a leap year if it's divisible by 4, except for century years. Century years (1900, 2000, 2100) are only leap years if divisible by 400. So 2000 was a leap year, but 1900 wasn't, and 2100 won't be. This correction keeps the calendar aligned with Earth's orbit around the Sun.
What Can You Calculate with Calendar Dates?
A calendar calculator handles several date-related tasks: finding future or past dates, calculating the duration between two dates, determining what day of the week a date falls on, and identifying week numbers. Here are common use cases:
- Project deadlines - Add 90 days to today's date for a quarterly deadline
- Contract expirations - Calculate when a 2-year contract ends
- Pregnancy due dates - Add 40 weeks (280 days) to the last menstrual period
- Lease renewals - Find dates 6 months or 1 year from the start date
- Invoice payment terms - Calculate Net 30, Net 60, or Net 90 payment dates
What Day Will It Be in 30 Days?
To find the date 30 days from now, enter today's date in the calendar calculator, select "Add" for the operation, enter 30 in the Days field, and click Calculate. The result shows the exact date plus the day of week - useful for deadline tracking without consulting a physical calendar.
Calculating Business Days vs Calendar Days
Calendar days include weekends and holidays - every day counts. Business days (or working days) typically exclude Saturdays, Sundays, and public holidays. A "Net 30" payment term usually means 30 calendar days, while "30 business days" would span about 6 calendar weeks. Always clarify which type applies to contracts and legal documents.
Days Remaining in the Year
The Day of Year result shows the position of any date within its year (1-365 or 1-366). Subtracting from 365 (or 366 for leap years) gives days remaining. This helps with annual goal tracking, budget planning, or counting down to year-end milestones.
How Do I Calculate the Number of Days Between Dates?
Use the "Days Between Two Dates" section above. Enter the start date and end date, then click Calculate Difference. The tool displays results in multiple formats: total days, weeks plus remaining days, months plus remaining days, and the full breakdown of years, months, and days.
For more advanced date and time calculations including hours and minutes, try our time calculator or hours calculator. For age-specific calculations, the age calculator provides detailed breakdowns.
Last Updated: January 2026 | Reviewed for accuracy