How to use the date calculator
- Choose what to calculate: the days between two dates, or a new date after adding or subtracting time.
- Pick the dates. The start date is set to today; the end date defaults to December 31 of this year.
- Decide whether to count the end date. Leave it unchecked for a normal “how many days until” count; check it to count both the first and the last day.
- To add or subtract, enter any mix of years, months, weeks and days. Months and years are applied first, then weeks and days.
- Read the results: total days, weeks and days, months and days, business days, and the federal holidays that fall in the range. Copy the link to share them.
How to count the days between two dates by hand
Break the span into months. Count the days left in the first month (including the start date), add the full length of each month in between, and finish with the days of the last month before the end date. Here is November 15, 2027 to March 10, 2028, which crosses the leap day of February 29, 2028:
| Part of the span | Days |
|---|---|
| Rest of November 2027 (from the 15th) | 16 |
| December 2027 | 31 |
| January 2028 | 31 |
| February 2028 | 29 |
| March 2028 1–9 | 9 |
| Total | 116 |
The total is 116 days (16 weeks, 4 days), or 117 if you count both dates. In calendar terms it is 3 months, 24 days. Of those days, 84 are weekdays, and 79 are business days after removing 5 observed federal holidays (Thanksgiving Day, Thu, Nov 25, 2027; Christmas Day, Fri, Dec 24, 2027; New Year’s Day, Fri, Dec 31, 2027; Birthday of Martin Luther King, Jr., Mon, Jan 17, 2028; Washington’s Birthday, Mon, Feb 21, 2028).
For long spans, calculators convert each date to a serial day number and subtract. This page uses the day number
N = 365Y + floor(Y/4) − floor(Y/100) + floor(Y/400) + floor((153M + 2)/5) + D; days between = N(end) − N(start)
- Y
- the year, minus 1 if the month is January or February
- M
- months counted from March: March = 0, April = 1 … January = 10, February = 11
- D
- day of the month
- N
- serial day number; the difference of two N values is the number of days between the dates
Starting the year in March puts February, the only month whose length varies, at the end, so the leap-year terms (Y/4, Y/100, Y/400) handle February 29 automatically. Because it uses whole numbers only, the result never shifts with time zones or daylight saving time.
Business days and federal holidays
Business days are Monday through Friday. The calculator also removes the 11 legal public holidays in 5 U.S.C. 6103 on the dates they are observed: when a holiday falls on a Saturday, most federal employees get the Friday before off; when it falls on a Sunday, the Monday after (OPM). A Saturday New Year’s Day is observed on December 31 of the previous year. Here are the dates for 2026 and 2027:
| Holiday | Rule | 2026 | 2027 |
|---|---|---|---|
| New Year’s Day | January 1 | Thu, Jan 1, 2026 | Fri, Jan 1, 2027 |
| Birthday of Martin Luther King, Jr. | Third Monday in January | Mon, Jan 19, 2026 | Mon, Jan 18, 2027 |
| Washington’s Birthday | Third Monday in February | Mon, Feb 16, 2026 | Mon, Feb 15, 2027 |
| Memorial Day | Last Monday in May | Mon, May 25, 2026 | Mon, May 31, 2027 |
| Juneteenth National Independence Day | June 19 | Fri, Jun 19, 2026 | Fri, Jun 18, 2027 (observed) |
| Independence Day | July 4 | Fri, Jul 3, 2026 (observed) | Mon, Jul 5, 2027 (observed) |
| Labor Day | First Monday in September | Mon, Sep 7, 2026 | Mon, Sep 6, 2027 |
| Columbus Day | Second Monday in October | Mon, Oct 12, 2026 | Mon, Oct 11, 2027 |
| Veterans Day | November 11 | Wed, Nov 11, 2026 | Thu, Nov 11, 2027 |
| Thanksgiving Day | Fourth Thursday in November | Thu, Nov 26, 2026 | Thu, Nov 25, 2027 |
| Christmas Day | December 25 | Fri, Dec 25, 2026 | Fri, Dec 24, 2027 (observed) |
That leaves 250 business days in 2026 (261 weekdays minus 11 holidays) and 249 in 2027. Banks, schools, states and private employers often follow different calendars — the Fair Labor Standards Act does not require paid holidays — so treat the federal list as a baseline.
Adding months: what happens at the end of a month
Adding days is exact, but months have 28 to 31 days, so “one month after January 31” needs a rule. This calculator keeps the same day of the month when it exists and otherwise uses the last day of the target month. It never rolls over into the following month. Years work the same way, so February 29 plus one year is February 28. When you enter months and days together, the months are added first, then the days.
| Start date | +1 month | +3 months | −1 month | +1 year |
|---|---|---|---|---|
| January 31, 2027 | February 28, 2027 | April 30, 2027 | December 31, 2026 | January 31, 2028 |
| January 31, 2028 | February 29, 2028 | April 30, 2028 | December 31, 2027 | January 31, 2029 |
| February 29, 2028 | March 29, 2028 | May 29, 2028 | January 29, 2028 | February 28, 2029 |
| March 31, 2027 | April 30, 2027 | June 30, 2027 | February 28, 2027 | March 31, 2028 |
| May 31, 2027 | June 30, 2027 | August 31, 2027 | April 30, 2027 | May 31, 2028 |
| August 31, 2027 | September 30, 2027 | November 30, 2027 | July 31, 2027 | August 31, 2028 |
Because of clamping, adding one month twice is not always the same as adding two months at once: January 31, 2027 + 1 month = February 28, 2027, and February 28, 2027 + 1 month = March 28, 2027, but January 31, 2027 + 2 months = March 31, 2027. Contracts and loan agreements sometimes define their own conventions, so check the wording when a deadline matters.
What date is 30, 60 or 90 days from today?
Counting from Tuesday, September 29, 2026. Business days skip weekends and observed federal holidays, and the start date is not counted.
| Add | Calendar days later | Business days later |
|---|---|---|
| 7 days | Tue, Oct 6, 2026 | Thu, Oct 8, 2026 |
| 10 days | Fri, Oct 9, 2026 | Wed, Oct 14, 2026 |
| 14 days | Tue, Oct 13, 2026 | Tue, Oct 20, 2026 |
| 30 days | Thu, Oct 29, 2026 | Thu, Nov 12, 2026 |
| 45 days | Fri, Nov 13, 2026 | Fri, Dec 4, 2026 |
| 60 days | Sat, Nov 28, 2026 | Mon, Dec 28, 2026 |
| 90 days | Mon, Dec 28, 2026 | Wed, Feb 10, 2027 |
| 100 days | Thu, Jan 7, 2027 | Thu, Feb 25, 2027 |
| 120 days | Wed, Jan 27, 2027 | Thu, Mar 25, 2027 |
| 180 days | Sun, Mar 28, 2027 | Mon, Jun 21, 2027 |
| 365 days | Wed, Sep 29, 2027 | Fri, Mar 17, 2028 |
For a different starting date, choose “Add or subtract” in the calculator. There are 7 days in a week, so 10 business days is usually two calendar weeks — a bit more when a federal holiday falls in between.
Days until the next holidays
See live countdowns for 12 US holidays, with the weekday and federal observed date for the next five years, on our days until holidays page. The next few:
- Days until Halloween: Saturday, October 31, 2026
- Days until Thanksgiving: Thursday, November 26, 2026
- Days until Christmas: Friday, December 25, 2026
- Days until New Year’s Day: Friday, January 1, 2027
- Days until Valentine’s Day: Sunday, February 14, 2027
- Days until St. Patrick’s Day: Wednesday, March 17, 2027
Days, weeks, months and years
- Weeks: divide the day count by 7; the remainder is the extra days. 93 days is 13 weeks, 2 days.
- Months: count whole calendar months from the start date, then the leftover days. September 29, 2026 to December 31, 2026 is 3 months, 2 days.
- Years: 365 days in a common year, 366 in a leap year; a year averages 365.2425 days under the Gregorian rules.
- Month lengths: 31 days in January, March, May, July, August, October and December; 30 in April, June, September and November; 28 or 29 in February.
To find an exact age from a birth date, use the age calculator. To total hours and minutes between two times or on a time card, use the hours calculator.
Frequently asked questions
How do I calculate the number of days between two dates?
Subtract the earlier date from the later one: count the days left in the first month, add the full days of every month in between, then add the days of the last month before the end date. For example, November 15, 2027 to March 10, 2028 is 16 + 31 + 31 + 29 + 9 = 116 days. Add 1 if you want to count both the start and end dates.
Does the date calculator include the end date?
Not by default. Like most day counts (loan interest, notice periods, “days until”), the calculator counts from the start date up to the end date, so Monday to Friday of the same week is 4 days. Check “Include the end date” to count both ends, which adds exactly one day — for a full calendar year that gives 365 or 366.
How many business days are in a year?
2026 has 261 weekdays (Monday–Friday). Removing the 11 federal holidays observed in 2026 leaves 250 business days. 2027 has 261 weekdays and 249 business days after 12 observed federal holidays (including any New Year’s Day holiday observed on December 31). Your employer’s holiday calendar may differ.
What is one month after January 31?
This calculator returns February 28, 2027: when the target month is shorter, the day is moved to that month’s last day. In a leap year, January 31 plus one month is February 29, 2028. The same rule gives February 28, 2027 for March 31 minus one month, and February 29 plus one year is February 28.
Are weekends and holidays counted as days?
Yes, calendar days include every day of the week. The results also show weekdays (Monday to Friday only) and business days, which additionally skip the 11 US federal holidays on their observed dates. State holidays, bank holidays and company holidays such as the day after Thanksgiving are not removed, so adjust by hand if you need them.
How do leap years affect the day count?
A leap year adds February 29, so any span that includes it is one day longer: February 1 to March 1, 2028 is 29 days instead of 28. Leap years are divisible by 4, except century years not divisible by 400 — so 2000 was a leap year and 2100 will not be. The calculator applies this rule automatically for any year from 1 to 9999.