Date Duration Calculator: Days, Weeks, Months and Years Between Dates
Date Duration Calculator
Find the duration between two dates in days, weeks, months and years. Add times of day for hours and minutes, see how many of each weekday fall inside the span, and copy a link that reopens the same calculation.
Start
End
Where the days fall
How many of each weekday
The same duration expressed as
By convention the count leaves out the start date and includes the end date, so Monday to Friday of the same week is 4 days. Years, months and days are found by stepping whole calendar months from the start date, pulling the day back to the last day of a shorter month when it has to, then counting the days left over. Times of day are read as wall clock times in your own time zone.
How to use the date duration calculator
Set a start date and an end date and the answer appears straight away: a day count at the top, then the same span in weeks, calendar months, hours and years underneath. You can enter the dates in either order. If the end comes first, the calculator swaps them and says so rather than handing you a negative number.
The setting people most often get wrong is the first checkbox. Left alone, the count skips the start date and includes the end date, which is how a question like how many days between two dates is normally answered, and why Monday to Friday of the same week comes out as 4. Tick Count both the start and end date when every day in the range stands on its own, such as a vacation booked Monday to Friday, which is 5 days off, not 4.
Tick Add times of day when hours matter. The dates then stop being whole days and the result is measured clock to clock. Copy link to this duration gives you an address that reopens the calculator on exactly the same dates, which is handy in an email, a project diary or a ticket.
What the calculation is doing
Behind the inputs, each date becomes a day number on one continuous calendar and the day count is a subtraction. There is no looping through months and no 30 day shortcut. The calendar is the Gregorian one with its full leap year rule: every fourth year gets a February 29, except century years, which only get one when they divide by 400. So 2000 had a leap day, 1900 did not, and 2100 will not.
The weekday figures come from the same day numbers. Any run of 7 consecutive days holds exactly one of each weekday, so the calculator takes the whole weeks first and then looks at the few days left over. That is why the weekday grid shows a mix of 30s and 31s for the default dates: 213 days is 30 weeks plus 3 extra days, and those 3 days land on a Friday, a Saturday and a Sunday.
Weekdays here means Monday to Friday. Public holidays are not taken out, because they depend on your province or state. When they need to come out, the Working Days Calculator carries the Canadian and US holiday lists.
Why the months answer is trickier than it looks
Days are unambiguous. Months are not, because they run anywhere from 28 to 31 days. This calculator steps whole calendar months forward from the start date, and when the target month is too short for the starting day, it pulls the day back to the last day of that month. That is the same rule phone calendars and most date libraries follow. Whatever is left after the last whole month is counted in days.
The rule has one quirk worth knowing about. January 31 to March 1, 2026 and January 30 to March 1, 2026 both come out as 1 month and 1 day, even though the first span is 29 days long and the second is 30. Both starting days get pulled back to February 28 before the leftover day is counted. The day total is always the figure to trust. Months and days is a readable way of saying it, not a separate measurement.
Other conventions exist, and they will disagree with a calendar count by a day or two around month ends. Some interest calculations use 30 day banking months. Spreadsheets have their own trap: Microsoft documents that DATEDIF with the MD unit can return a negative number, a zero or an inaccurate result. When a contract says months, the calendar convention used here is almost always what was meant. When a loan agreement says it, read the fine print.
A worked check you can repeat on paper
Take the default dates, January 1, 2026 to August 2, 2026. Count what is left of each month: 30 days of January after the 1st, then 28, 31, 30, 31, 30 and 31 for February through July, then 2 days of August. That is 30 + 28 + 31 + 30 + 31 + 30 + 31 + 2 = 213 days.
In weeks, 213 ÷ 7 is 30 with 3 left over, so 30 weeks and 3 days. In calendar months, January 1 plus 7 months is August 1, and one more day reaches August 2, so 7 months and 1 day. In hours, 213 × 24 = 5,112. A Gregorian year averages 365.2425 days over its 400 year cycle, so the span is 213 ÷ 365.2425 = 0.583 years.
For weekdays, the 30 full weeks contribute 150. The 3 leftover days are Friday, Saturday and Sunday, which adds one more weekday for 151, and the remaining 62 are weekend days. The calculator shows exactly these numbers with its default inputs, so if yours differ, check the counting convention first.
Adding times of day
With times switched on, the calculator measures from one moment to the other. Friday, March 6, 2026 at 21:30 to Monday, March 9, 2026 at 06:15 is 2 days, 8 hours and 45 minutes, or 56.75 hours. The option to count both dates is switched off in this mode, since a clock to clock measurement already says exactly what it covers.
That example hides a trap. Across most of Canada and the US the clocks go forward at 2:00 on Sunday, March 8, 2026, so anyone who actually lived through that span experienced 55.75 hours, not 56.75. The calculator reports wall clock time, because that is what timesheets, bookings and schedules use, but it checks your own time zone and flags any clock change inside the span, with the real elapsed time alongside.
For shifts that cross midnight and need regular and overtime hours split out, the Timesheet Duration Calculator is the better fit.
Mistakes that catch people out
Off by one on the convention. Whether the first day counts changes the answer by one, every single time. A notice period of 30 days almost never counts the day the notice arrives, while a 5 day vacation from Monday to Friday counts both ends. Decide which question you are asking before you read the number.
Assuming a month is 30 days. Seven months from January 1 is August 1 whatever the day counts say, and 7 × 30 is 210, three short of the true 213. Use calendar months for dates, day counts for durations, and never multiply one into the other.
Forgetting leap years in long spans. Every span that crosses a February 29 gains a day over the 365 per year estimate. 2024 and 2028 are leap years. 2100 is not, even though it divides by 4, and that catches out homemade spreadsheets.
Estimating working days as five sevenths of the total. It is close on long spans and wrong on short ones. Three days starting on a Friday hold one weekday, not 2.14. The weekday grid counts actual dates, so use it instead of the ratio.
Trusting spreadsheet dates before March 1900. Excel treats February 29, 1900 as a real day, a choice made long ago for compatibility with Lotus spreadsheets. Any day count in Excel that starts before March 1, 1900 is off by one. This calculator uses the true Gregorian calendar and does not carry that error.
Comparing countdowns across time zones. Days until and days since are counted from today in your own time zone, so someone in Halifax and someone in Vancouver can see different numbers for a few hours each night. Neither is wrong; they just have different todays.
How many days until Christmas and other holidays
Countdowns to the holidays people ask about most in Canada and the US. Each link opens the date duration calculator from today to the next occurrence, and rolls forward to the following year once the day has passed, so the answer never goes stale. Moveable holidays such as Easter, Victoria Day and both Thanksgivings are worked out from their rules each year rather than copied from a table.
Countdowns to a season, a month, a weekday or a new year
Season links use the actual equinox and solstice times, converted to your own time zone. That is why the first day of fall 2026 is September 22 in Halifax but September 23 in London. Month and weekday links always point at the next one coming, and the year links count to January 1.
How many days since
These count back from today. The holiday links use the most recent occurrence, so days since Christmas means the last Christmas, not the one coming. The dated links are fixed points, including the Unix epoch that computer clocks count from and the day of the first Moon landing.
Days between common dates
Fixed spans that come up in planning, budgeting and reporting. The quarter and half year links count both the first and the last date, since a quarter is meant to include all of its days. The year to year links count the usual way, which is why 2024 to 2025 shows 366 and January 1 to December 31, 2026 shows 364.
How this was checked
The day count was tested against a brute force count that walked the calendar one day at a time, on 3,000 random pairs of dates between 1900 and 2100, half of them with the count both dates option ticked. Every total and every weekday tally matched.
The months and days figure was checked from the other direction. For each random pair, adding the reported months to the start date and then the reported days had to land exactly on the end date, and adding one more month had to overshoot it. That confirms the answer is always the largest whole number of months, which is what 7 months and 1 day should mean.
Holiday rules were checked against published 2026 dates, including Easter on April 5, Victoria Day on May 18, Labour Day on September 7, Canadian Thanksgiving on October 12 and US Thanksgiving on November 26, and Easter was checked against known dates for eleven years between 2000 and 2038. Equinox and solstice times follow the method in Jean Meeus, Astronomical Algorithms, and land within a minute of the published 2026 times, for example the September equinox at 00:05 UTC on September 23.
Common questions
How do I work out the duration between two dates?
Enter a start date and an end date. The calculator subtracts one from the other on the real calendar, so month lengths and leap days are handled for you, and shows the result in days, weeks, months and years. By default the start date is not counted and the end date is.
Does the date duration calculator include the end date?
Yes. The end date is included and the start date is left out, which is the standard way to count the days between two dates. Tick Count both the start and end date to include the start date as well, which adds exactly one day.
How many weekdays are there between two dates?
The calculator counts every Monday to Friday inside the span and shows a separate tally for each day of the week. It does not remove public holidays, because those depend on where you are. Use the Working Days Calculator when statutory holidays must come out.
Why do different calculators give different month counts?
Months run from 28 to 31 days, so there is more than one way to count them. This tool steps whole calendar months from the start date and pulls the day back to the month end when a month is too short. The total in days is the same everywhere; only the months and days split can differ.
Can it calculate hours and minutes between two dates?
Yes. Tick Add times of day and enter a time for each date. The result is measured clock to clock, and the calculator warns you when a daylight saving change inside the span makes the real elapsed time an hour different.
Do the countdown links stay correct next year?
Yes. Links such as days until Christmas are worked out from today every time the page opens, and they roll forward to the next occurrence once the day has passed.
Related Calculators and Reference
- Days From Today Calculator: the reverse question, when you know the number of days and need the date it lands on.
- Add or Subtract Days Calculator: shift a date forward or back by calendar days or working days.
- Working Days Calculator with Canadian and US Holidays: business day counts with statutory holidays taken out.
- Age Calculator: the same years, months and days method applied to a date of birth.
- Timesheet Duration Calculator: hours worked across shifts, with the overtime split.
- Time Calculator: hours and minutes between two clock times on the same or next day.
- Time Zone Converter: meeting times across time zones.
- Due Date Calculator: pregnancy due date and weeks from the last period.
- Week Number Calculator: the ISO week number of any date.
- Days Until Calculator: count down to Christmas, a holiday or any future date.
- ISO 8601 date and time format: the international standard for writing dates, times and durations without ambiguity.