Count down to an event, find the interval between two dates, or add and subtract calendar and business days. Choose the mode that matches your task; each one states its counting rules. Fields marked as optional can use today's date, and the Add/Sub reference table shows common calendar-day offsets from your start.
US federal holidays
| Holiday | Rule |
|---|---|
| New Year's Day | January 1 (observed) |
| Martin Luther King Jr. Day | 3rd Monday of January |
| Presidents' Day | 3rd Monday of February |
| Memorial Day | Last Monday of May |
| Juneteenth | June 19 (observed) |
| Independence Day | July 4 (observed) |
| Labor Day | 1st Monday of September |
| Columbus Day | 2nd Monday of October |
| Veterans Day | November 11 (observed) |
| Thanksgiving Day | 4th Thursday of November |
| Christmas Day | December 25 (observed) |
Examples
Days from January 1, 2024 to June 17, 2026
The span is 2 years, 5 months, 16 days — 898 days, or 128 weeks and 2 days. Of those, 642 are weekdays and 617 are business days once observed US federal holidays are excluded.
Adding 10 business days to June 17, 2026
Starting Wednesday, June 17, 2026 and adding 10 business days (skipping weekends and Juneteenth on June 19) lands on Thursday, July 2, 2026.
Formula
Days between counts whole years and months by the calendar, then the leftover days; the same span is also given as total days and weeks. Business days are the weekdays in the span, optionally net of observed US federal holidays.
years/months = whole calendar months from start to end (day-clamped)
days = end − (start + whole months)
total days = end − start total weeks = total days ÷ 7
business days = weekdays in (start, end] (− observed federal holidays)
Add / subtract applies years and months first (clamped to the month's last day), then weeks, then days — counted as calendar or business days.
Calendar and holiday limits
Date addition uses Gregorian calendar arithmetic. Business-day mode recognizes the listed US federal holiday dates and weekends; it does not know an employer's closure calendar, state holidays, market holidays, or holidays observed outside the United States. Confirm deadlines with the authority that controls them. The US Office of Personnel Management publishes the federal holiday schedule used as the reference.
Birthdays and weekdays
Use the Age Calculator when the starting date is a birth date and you need completed years, months, and days. If you only need to identify the weekday of a date, the Day of the Week Calculator gives that answer directly.
Days until an event
Choose Countdown to count calendar days until your own target date or the next New Year's Day, Halloween, or Christmas Day. A preset uses the first occurrence on or after the reference date; if the event is on that date, the gap is zero. Custom event dates in the past show how many days ago they occurred.
The primary result is the calendar gap. Selected days counted can include all days, Monday to Friday, or your own set of weekdays. Its default interval excludes the earlier date and includes the later one. The checkbox also includes the earlier date if it is a selected weekday. It does not change the underlying calendar gap. Holidays are not removed from the countdown's weekday filter; use the existing business-day results for the separately labeled US holiday calculation.
For example, Friday, September 25, 2026 to Monday, September 28, 2026 is 3 calendar days. Counting only Monday to Friday gives 1 selected day under the default convention, or 2 when the earlier date is also counted. Selecting only Saturday and Sunday gives 2 selected days.
The countdown uses dates, not hours or minutes, and it does not tick continuously. A blank reference date uses today when the form loads. Custom event names are optional and appear in the result; using Share includes entered values in the link. Presets use calendar dates rather than observed public-holiday dates. The countdown supports dates from year 1000 through 9900.
Dates from today: quick reference
In Add/Sub, leave the start date blank for today and enter the desired offset in Days. The quick-reference table lists 7, 14, 21, 28, 30, 60, 90, 180, and 365 calendar days from the chosen starting date. Selecting Subtract makes those offsets negative. The table is independent of any years, months, weeks, or business-day settings in the main calculation and is explicitly labeled as calendar days.
For example, adding 2 calendar days to February 28, 2024 gives March 1, 2024 because 2024 includes February 29. Adding 30 days is not generally the same as adding one month. Use the Months field when a calendar-month interval is the intended rule.
For a personal elapsed-time tracker with calendar anniversaries and milestone dates, use the Sobriety Calculator. Use the Time Duration Calculator for time-of-day intervals. Avoid treating this general date arithmetic as a substitute for an institution's deadline rules.
Days and time between dates
The Date & time tab adds 24-hour clock inputs and optional weekday/date exclusions. Enter times as HH:MM, such as 09:30 or 17:00. The result separates the full elapsed interval from included hours after filters. The interval starts at the first instant and ends just before the final instant. Include end day extends the endpoint by 24 hours.
From Friday January 2, 2026 at 09:00 to Monday January 5 at 17:00 is 80 elapsed hours. Counting only Monday–Friday includes 15 hours on Friday and 17 hours on Monday: 32 hours total. Excluding January 5 reduces the included time to 15 hours. This counts selected calendar hours, not working shifts; it does not assume an eight-hour working day.
Date-only counts versus clock intervals
Between retains the original calendar days, years/months/days, and business-day outputs, including its separate US federal holiday count. Date & time uses only the weekdays and excluded dates you supply. A same-day 09:00–17:00 interval is eight hours, while the date-only elapsed gap is zero days.
These clock intervals use fixed 24-hour days in one assumed timezone. They do not adjust for daylight-saving changes or different timezone offsets. For a timezone-aware travel interval, first put both instants on a common fixed-offset time basis. Fractional-day output divides the included hours by 24; it is not a count of calendar dates touched.