Day Counter
Day Counter Calculator Overview
The Day Counter or Days Calculator can be used for many purposes, such as:
Counting down to a birthday
Tracking pregnancy days
Calculating business days left for a project
Finding the total number of days between two dates
How to Use the Day Counter
Select Dates – Use the date pickers to choose a Start Date and End Date.
Include End Day – Tick the “Include End Day” box if you want the last day counted.
Example: If your project is due at 11:59 PM on April 24 and today is March 29, select those dates and check the box.
Alternatively, choose April 25 as the end date and leave the box unchecked for the same result.
Additional Settings – Click Settings to:
Include or exclude holidays
Select common US holidays or enter your own custom holidays
What the Calculator Does
Calculates the total days between two dates, assuming a Monday–Friday work week and weekends on Saturday–Sunday.
Breaks results into weekdays and weekend days by default.
Can include holidays in both the count and list.
Always counts the start date as a full day.
Counts the end date if the Include End Day box is checked.
Counting Days from a Specific Date
You can also:
Select a start date and add or subtract a number of days.
Choose whether to count business days only (excludes weekends).
Example: If you start on Monday, add 7 business days, and exclude weekends, your result will be the following Wednesday.
Day of the Week Feature
The calculator also tells you the day of the week for your chosen dates.
One method to determine this is called the Doomsday Rule, created by mathematician John Conway.
The Doomsday Rule
The rule is based on “doomsdays”—specific dates that always fall on the same weekday in a given year.
These dates are fixed for every year, but the weekday changes each year.
Doomsdays by Month
| Month | Doomsday Date | Leap Year Change |
|---|---|---|
| Jan | 1/3 | 1/4 |
| Feb | 2/28 | 2/29 |
| Mar | 3/14 | – |
| Apr | 4/4 | – |
| May | 5/9 | – |
| Jun | 6/6 | – |
| Jul | 7/11 | – |
| Aug | 8/8 | – |
| Sep | 9/5 | – |
| Oct | 10/10 | – |
| Nov | 11/7 | – |
| Dec | 12/12 | – |
Tips to Remember
Even months (except Feb) match their day and month (e.g., 4/4, 6/6, 8/8).
February’s doomsday is the last day of the month.
January’s is Jan 3 (or Jan 4 in leap years).
March’s is 3.14 (Pi Day).
“I work from 9 to 5 at 7-11” → helps remember May (5/9), September (9/5), July (7/11), November (11/7).
Anchor Days
An anchor day is the doomsday for a century. For example:
1900 → Wednesday
2000 → Tuesday
2100 → Sunday
2200 → Friday
These repeat every 400 years.
Doomsday Rule Calculation Steps
Find the anchor day for the century. Call it a.
Divide the last two digits of the year by 12. Call the result b (ignore remainder).
Take the remainder as c.
Divide c by 4 (ignore remainder) to get d.
Add a + b + c + d to get e.
Reduce e by subtracting 7 until it’s 0–6. This is f, the doomsday weekday.
Find the nearest doomsday to your date and count forward or backward to determine the weekday.
Example: What day was 3/15/2292?
a = Friday (5)
92 ÷ 12 = 7 → b = 7
Remainder = 8 → c = 8
8 ÷ 4 = 2 → d = 2
e = 5 + 7 + 8 + 2 = 22
22 – (7×3) = 1 → f = 1 (Monday)
Nearest doomsday to 3/15 is 3/14 (Monday)
3/15 is one day after → Tuesday
Answer: 3/15/2292 was a Tuesday.
Related Calculators:
Time Duration Calculator, Time Zone Converter
External Resources:
Day Counter Calculator on Calculator.net
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