data tool
Date difference calculator
Pick a start date and an end date and see the gap as a number of days, as weeks and days, as calendar months and days, and as weekdays with weekends left out. Tick one box to count the end date as well, the way notice periods and bookings are often counted.
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- Runs on your device, nothing is uploaded
- Free, no sign in
- No watermark, no file limit
How it works
- 1
Pick the start date
Use the date picker in Start date, or press Start today. The tool opens on 31 January to 15 March to show how months are counted.
- 2
Pick the end date
If it is earlier than the start, the two are swapped and a note says so.
- 3
Decide about the end date
Leave Count the end date too unticked for the gap between two dates. Tick it when both the first and the last day count, as in a stay or a notice period.
- 4
Read and copy
The summary line gives the days with both dates written out, and six cards give the other forms. Copy the result takes all of it as text.
Counting the end date or not
From 1 March to 2 March is one day apart and two days long, and both answers are right for different questions. The gap between two dates, how long until or how long since, leaves the end date out. A span of days that are all used, such as a hotel stay, a leave request or a notice period that runs from the day after notice is given to the last day of work, counts both ends. Read what your contract or policy says: phrases such as inclusive, clear days and not less than change the count by one day either way.
How months are counted
A month is not a fixed number of days, so a gap in months depends on where it starts. The tool counts whole calendar months forward from the start date for as long as they fit, then counts the days left over. From 15 January, one month later is 15 February. From 31 January there is no 31 February, so the month ends on the last day of February, 28 in 2026 and 29 in a leap year, and the leftover days are counted from there. That is how most people and most contracts read one month after the 31st, and the tool shows a note when it happens.
Weekdays and weekend days
The weekday count includes every Monday to Friday in the range and leaves out Saturdays and Sundays, using the same start and end rule as the day count. It does not know about public holidays, office closures or a working week that runs Sunday to Thursday. For a deadline that has to skip those days, the business days calculator takes a pasted list of holidays and lets you choose which days are the weekend.
Putting the dates into a document
A notice letter, a lease or a payment schedule usually needs both the dates and the period written out, and the two have to agree. Work out the period here, then put the exact dates into the document rather than only a number of days, so nobody has to repeat the arithmetic. In Australia, for example, the minimum notice an employer must give runs from one to four weeks depending on length of service, with an extra week for older long serving staff, so the end date moves with the facts of each case.
Limits worth knowing
Dates are counted as whole calendar days in UTC, so a daylight saving change between the two dates cannot turn 30 days into 29 days and 23 hours. Leap years are handled, so a range that crosses 29 February counts it. Every date is in the Gregorian calendar, so dates before a country adopted it, such as 1752 in Britain, will not match historical records. Nothing is uploaded and nothing is stored, ever.
Limits
- Month arithmetic follows the calendar, so 31 January plus one month is 28 or 29 February, and months from the 31st are counted to the last day of shorter months.
- Weekdays are Monday to Friday. Public holidays are not known; the business days calculator takes a pasted list.
- Whole days only: times of day are not entered, so a clock change in between never adds or removes an hour.
What it does not do
- It does not add a number of days to a date; the business days calculator does that, with or without weekends.
- It does not know any country's public holidays.
- It does not work in calendars other than the Gregorian one.
Questions people ask
How many days until a date, counting today?
Set the start date to today with Start today and the end date to the day you are counting to. The days figure is the number of sleeps, so to speak: today is not counted and the end date is. If you want both today and the target day counted, tick Count the end date too and the figure goes up by one.
How do I calculate someone's age in years, months and days?
Put the date of birth as the start date and today, or another date, as the end date. Read the Years, months, days card. Someone born on 29 February is counted to 28 February in years that are not leap years, the same rule the tool uses for any month end. Some laws use 1 March instead, so check if the exact day matters.
Why do two websites give different month counts for the same dates?
Because there is more than one reasonable rule. Some calculators count a month only when the day number is reached again, so 31 January to 28 February is 0 months and 28 days. Others, like this one, let a month end on the last day of a short month, giving 1 month. Check which rule your contract assumes.
How many weeks pregnant am I from a date?
Pregnancy is usually counted from the first day of the last menstrual period, not conception. Enter that date as the start and today as the end, and read Weeks and days. Treat the result as a rough guide only, since your midwife or doctor may date the pregnancy from an ultrasound scan, which is more accurate.
Does the calculator send my dates anywhere?
No. The arithmetic runs in this page on your device and no network request carries the dates. Nothing is written to storage either, so the dates in a dispute, a medical history or a contract you are checking leave nothing behind when the tab is closed.
Write the dates into a notice letter
Take what you made here into documents.
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Background reading: the question page on this.
Written and checked by the OneCraft team. Last checked .