Date Difference Calculator
Calculate the number of days, weeks, months and years between any two dates.
The date difference calculator counts the days between two dates, which is useful for project timelines, notice periods, pregnancy planning, event countdowns and leave calculations. It automatically accounts for leap years and different month lengths.
How to use the calculator
- Choose the start date.
- Choose the end date.
- Get the exact number of days between them.
- The same duration is also shown in weeks, months and years.
How it is calculated
Weeks = days ÷ 7, months ≈ days ÷ 30.44 and years ≈ days ÷ 365.25 (averages that account for leap years).
Worked example
From 1 January 2026 to 31 March 2026
Total days = 89
That is about 12.7 weeks, 2.9 months or 0.24 years.
Who should use this calculator
- Anyone serving a notice period and counting the exact last working day.
- Project managers working out elapsed days between two milestones, or how long a phase actually ran.
- Tenants, landlords and borrowers checking how many days remain in a term or a grace period.
- Anyone planning leave, travel or an event and needing the day count across months of different lengths.
Common mistakes to avoid
- Counting the end date twice. The difference between two dates does not include the start date. If a service starts on 1 January and ends on 31 March, you may want to add one day depending on whether both dates count.
- Assuming every month has 30 days. February has 28 or 29 days, and a difference of "three months" can be 89, 90 or 92 days depending on which months they are.
- Mixing calendar days with working days. A 30-day notice period usually means calendar days, while a project deadline may mean business days. They are rarely the same number.
- Forgetting public holidays. Working-day counts need holidays removed as well as weekends, and the list differs by state and year.
- Ignoring leap years in long spans. A multi-year difference that ignores 29 February is out by a day every four years or so.
Calendar days and working days are different counts
From 1 January 2026 to 31 March 2026 is 89 calendar days — about 12.7 weeks, 2.9 months or 0.24 years. Those conversions are averages: a month is not exactly 30.44 days and a year is not exactly 365.25, which is why the day count is the trustworthy figure and the rest are approximations.
If what you actually need is working days, subtract weekends and public holidays from the 89. That number is what matters for project deadlines, payment terms and leave balances, and it can be six or seven days lower than the calendar count even in a short period. Calculate in days first, then convert — never the other way round.
Date difference terms explained
- Calendar days
- Every day between two dates, including weekends and holidays.
- Working days
- Days excluding weekends and public holidays. This is what deadlines and payment terms usually refer to.
- Inclusive counting
- Counting both the first and last day, which is one more than the difference and is common in contracts.
- Leap year
- A year with 29 February, which adds one day to spans that include it.
- Notice period
- The period an employee must work after resigning, counted in calendar days unless the contract says otherwise.
- Elapsed time
- The total time between two points, usually measured in days because weeks and months are imprecise units.
- Grace period
- An extra window after a deadline during which a payment or action is still accepted without penalty.
Questions this calculation answers
How many days between today and a deadline? How long has a project actually been running, in calendar and working days? Does a 30-day notice period end before or after a public holiday? How many weeks remain until an exam or a closing date? Each of these is the same calculation with a different pair of dates, and the important step is always the same: take the day count first, then convert to weeks or months only as an approximation. Months are the least reliable unit because their length varies, which is why contracts and notifications almost always specify days.
Frequently asked questions
Does the calculator count the end date?
The result is the difference between the dates, so the end date itself is not counted as an extra day. For an event on the end date, you may want to add one day.
Are leap years handled?
Yes. February 29 is counted in leap years, so the day count stays accurate across long periods.
Can I count working days only?
This tool counts all calendar days. For business days, subtract weekends and public holidays from the total, or use a dedicated working-days calculator.