Calculate Duration Between Dates
Enter two dates to find the exact duration between them.
How the Date Duration Calculator Works
Four steps to find the exact duration between any two dates.
Enter Start Date
Pick the earlier date you want to measure from. This is the beginning of your duration period.
Enter End Date
Pick the later date. Click "End = Today" to use the current date. You can also swap dates if needed.
Calculate
Click "Calculate Duration" to compute the result. The tool uses calendar-aware arithmetic for precision.
View Results
See the duration in years/months/days, total days, weeks, hours, minutes, and business days.
What Is a Date Duration Calculator?
Understanding date-based duration calculations.
Date duration basics
A Date Duration Calculator measures the exact time span between two calendar dates. Unlike a simple day counter, it breaks the result into years, months, and days — not just a single number.
The calculation accounts for variable month lengths. The duration from January 31 to March 31 is "2 months" even though January has 31 days and February has 28 (or 29). Each month is treated as one complete unit.
Calendar-aware arithmetic
The Gregorian Calendar has irregular month lengths and leap year rules. Simple division (total days ÷ 30 for months) gives incorrect results. This calculator uses proper calendar subtraction: years first, then months, then remaining days.
Total conversions
The results also show total days (exact count), total weeks (days ÷ 7), total hours (days × 24), and business days (weekdays only). These alternative formats serve different use cases. Count just the days in that span with the days between dates calculator.
When to Use a Date Duration Calculator
Common date duration scenarios.
Contract Length
Verify the exact duration of a contract — lease agreements, employment terms, subscription periods — in years, months, and days.
Academic Terms
Calculate the length of school semesters, terms, or years. Know exactly how many days and weeks remain in the academic period.
Employment Duration
Calculate your tenure at a job for resumes and HR purposes. Express experience in years and months accurately.
Mortgage & Loans
Track remaining loan duration. See how many months and days are left on a mortgage or car payment schedule.
Travel Planning
Calculate trip length in days and weeks. Plan itineraries by knowing exactly how long you'll be away from home.
Medical Tracking
Track treatment duration, recovery periods, or time since a medical procedure. Doctors often need exact durations for records.
Date Duration Examples
Common date-to-date duration calculations.
New Year to mid-year
Jan 1 → Jul 1 = 6 months, 0 days = 181 days (182 in leap year).
Full year
Jan 1, 2025 → Jan 1, 2026 = exactly 1 year = 365 days.
Quarter duration
Jan 1 → Apr 1 = 3 months = 90 days (91 in leap year). Standard fiscal quarter.
Semester length
Sep 1 → Dec 15 = 3 months 14 days = 105 days. Typical fall semester.
Step-by-Step Walkthrough
One period expressed six different ways, with a clear line drawn between the exact figures and the approximate one.
An employee’s probation period runs from 14 April 2025 to 14 October 2025. How long is that in every unit that might be asked for?
Count the exact days
16 (Apr) + 31 (May) + 30 (Jun) + 31 (Jul) + 31 (Aug) + 30 (Sep) + 14 (Oct) = 183 daysEvery month contributes its true length. This day count is the foundation — every other figure below is derived from it, so it has to be exact.
Running total183 days
Convert to weeks
183 ÷ 7 = 26.14 weeksExact, because a week is always seven days. Just over twenty-six weeks — a useful figure when review cycles run weekly or fortnightly.
Running total26.14 weeks
Convert to hours and minutes
183 × 24 = 4,392 hours 4,392 × 60 = 263,520 minutesAlso exact. These units matter for anything where the period is a continuous quantity — accrual, interest, service credit — rather than a set of dates.
Running total4,392 hours
Count the business days
183 ÷ 7 = 26 weeks remainder 1 26 × 5 = 130, plus the remainder day → 131Twenty-six complete weeks give exactly 130 weekdays. The single leftover day is a Tuesday here, so it counts — a remainder falling on a weekend would not.
Running total131 business days
Approximate the months
183 ÷ 30.44 ≈ 6.01 monthsAlmost exactly six months, which matches the calendar dates. But this agreement is a coincidence of the period chosen — the same 183 days starting in November would not land so neatly.
Running total≈ 6.01 months
14 April to 14 October 2025 is 183 days: 26.14 weeks, 4,392 hours, 131 business days and approximately 6 months. Only the last figure is an estimate.
Common Mistakes and Pro Tips
Mistakes that quietly corrupt your numbers
Treating "six months" and "183 days" as the same thing in an agreement.
Use whichever the agreement specifies, and derive the actual end date from it.
Why it matters: Six months from 31 August is 28 February — 181 days. Six months from 1 March is 1 September — 184 days. The gap moves by several days depending on the start date, which matters when a probation or notice period ends.
Deriving an end date by adding the approximate month figure.
Add calendar months directly, then read off the resulting date.
Why it matters: The 30.44-day average is designed for describing magnitude, not for date arithmetic. Adding 6.01 averaged months to a date produces something that is close to right and reliably not exact.
Assuming business days scale as five sevenths of the total.
Compute whole weeks first, then check the remainder against the calendar.
Why it matters: Five sevenths of 183 is 130.7, but the true figure depends entirely on which weekday the period starts on. Two identical-length periods can differ by two business days.
Reporting hours and minutes for a period measured in months.
Match the unit to the question — days or weeks for a probation period.
Why it matters: 263,520 minutes is exact and completely unusable in a conversation about employment. False precision obscures the answer rather than sharpening it.
Pro tips
Let the day count be the source of truth
Every other unit is derived from it. When two figures disagree, recheck the day count first — it is almost always where the error is.
Use dates for anything binding
Contracts, notice periods and probation should name an end date, not a duration. A date cannot be interpreted two ways; "six months" can.
Quote business days for delivery
Delivery and turnaround commitments are almost always understood in working days. Quoting calendar days for a two-week task promises something you did not mean.
Match precision to audience
Weeks for planning, days for contracts, hours for accrual. Reporting a six-month period in minutes is exact and unhelpful.
Take out holidays separately
Business days here exclude weekends only. Public holidays and shutdowns come off afterwards and can easily remove a further week over six months.
Note whether a leap day falls inside
Any period spanning 29 February gains a day. It is small, silent, and exactly the sort of thing that makes two calculations disagree by one.
Standard Periods and Their Exact Durations
Common contractual and planning periods with their real day counts, showing how much "a month" actually varies.
| Period | Days | Weeks | Hours | ≈ Business days |
|---|---|---|---|---|
| 1 week | 7 | 1.00 | 168 | 5 |
| 2 weeks | 14 | 2.00 | 336 | 10 |
| 1 month (28 d) | 28 | 4.00 | 672 | 20 |
| 1 month (30 d) | 30 | 4.29 | 720 | 22 |
| 1 month (31 d) | 31 | 4.43 | 744 | 23 |
| 6 weeks | 42 | 6.00 | 1,008 | 30 |
| 90 days | 90 | 12.86 | 2,160 | 64 |
| 1 quarter (91 d) | 91 | 13.00 | 2,184 | 65 |
| 4 months | 122 | 17.43 | 2,928 | 87 |
| 6 months (183 d) | 183 | 26.14 | 4,392 | 131 |
| 9 months | 273 | 39.00 | 6,552 | 195 |
| 1 common year | 365 | 52.14 | 8,760 | 261 |
| 1 leap year | 366 | 52.29 | 8,784 | 262 |
| 18 months | 548 | 78.29 | 13,152 | 391 |
| 2 years | 730 | 104.29 | 17,520 | 522 |
No rows match that filter.
Note the three "1 month" rows — 28 to 31 days, a spread of three business days. That variation is why contracts should name dates rather than month counts. For a straight day count without the unit breakdown, use the days between dates calculator.
Duration Between Dates, in Depth
Which units are exact, which are conventions, and how to choose.
The exact and the approximate
Days, weeks, hours and minutes convert between one another exactly. Every one of those figures is a fact about the interval.
Months are different. A calendar month is 28 to 31 days, so any month figure is either an average or a count of calendar months — and those two definitions disagree.
The practical rule: use exact units for anything computed or contractual, and month figures only when describing scale to a human. Mixing the two is where date arithmetic quietly stops being reliable.
How contracts actually define periods
Legal drafting avoids ambiguous durations wherever possible. Common approaches include naming an explicit end date, specifying a number of days, or using "calendar months" with a stated rule for month-end dates.
That last case needs the rule because six months from 31 August has no exact equivalent — 31 February does not exist. The usual conventions are to take the last day of the target month, or to roll forward to the 1st.
Where a period governs something consequential — notice, probation, limitation — the safest formulation is a date. Everything else invites interpretation.
Business days and why the remainder matters
Business-day counts decompose into two parts: complete weeks, which always contribute exactly five weekdays, and a remainder of up to six days, which contributes anywhere from zero to five.
The remainder depends entirely on the starting weekday. A period of 183 days beginning on a Monday and one beginning on a Saturday have different business-day counts despite identical length.
This is why a business-day figure cannot be estimated by scaling, and why two people counting the same period sometimes disagree by a day or two.
Choosing the right unit for the job
Each unit answers a different kind of question:
- Days — contracts, notice periods, anything legally defined
- Weeks — planning and sprint cycles, the most natural human scale
- Business days — delivery commitments and turnaround times
- Hours — accrual, service credit, continuous quantities
- Months — description and comparison only
Reporting all of them at once, as this calculator does, lets you pick — but the answer you communicate should usually be one of them, chosen deliberately.
Frequently Asked Questions
Common questions about the Date Duration Calculator.
How do I calculate the duration between two dates?
Enter a start date and end date. The calculator computes the exact difference in years, months, days, weeks, total days, and total hours. It handles varying month lengths and leap years automatically.
Does it count the start and end dates?
The calculator counts the days between the two dates (exclusive of both). If you need to include the start or end date, add 1 to the result. For example, Jan 1 to Jan 3 = 2 days between, or 3 days inclusive.
How does it handle leap years?
The calculator uses Gregorian calendar rules. February has 29 days in leap years (divisible by 4, except centuries not divisible by 400). This is factored into all month and year calculations.
Can I calculate duration in only one unit?
Yes. The results show total days, total weeks, and total hours alongside the broken-down years/months/days format. Use whichever unit suits your needs.
What about months with different lengths?
January has 31 days, February 28 or 29, April 30, etc. The calculator accounts for all these variations. "1 month" from January 31 takes you to February 28 (or 29 in a leap year).
Is this date duration calculator free?
Yes, completely free. No sign-up or downloads required. All calculations happen in your browser — your data is never sent to any server.
Why is the month figure approximate when the others are exact?
Because calendar months vary from 28 to 31 days, so no single conversion factor is correct. The calculator uses an average of 30.44 days, which describes scale well but should not be used to derive a date.
Is six months always 183 days?
No. Six months from 14 April is 183 days, but six months from 31 August is 181 and from 1 March is 184. The figure depends on which months the period spans, which is why contracts should name an end date rather than a duration.
How is the business-day count worked out?
Complete weeks contribute exactly five weekdays each, then the remaining days are checked against the calendar. Because the remainder depends on the starting weekday, two periods of identical length can have different business-day totals.
Are public holidays excluded from business days?
No, only weekends are. Holiday calendars differ by country, region and organisation, so subtract your own public holidays and closures from the business-day figure separately.
Which unit should I use for a contract?
Days, or better still an explicit end date. Days are unambiguous and legally precise, whereas month counts require a further convention for cases like six months from 31 August, where the target date does not exist.