Date Difference Calculator
Find the exact time between two dates, including business days, or add and subtract days, weeks and months from a date. Free, instant, private.
Two modes doing two different jobs
The first mode measures a gap you already know the ends of. The second one projects a date you do not know yet. They use different arithmetic and have different quirks, so it is worth reading both sections below.
Worked example: 10 February to 1 June 2026
Enter 10 February 2026 as the start and 1 June 2026 as the end. Here is every figure the tool produces and where it comes from.
3 months, 22 days. Subtract the parts: June (6) minus February (2) is 4 months, and 1 minus 10 is -9 days. Because the day count went negative, a month is borrowed from May, which has 31 days, giving 22 days and reducing the months to 3.
111 total days. This is the straight millisecond difference divided by the length of a day and rounded, so it is unaffected by how the months break down.
15 total weeks. 111 divided by 7 is 15.86, rounded down. The leftover 6 days are not shown anywhere, which is deliberate: the card counts whole weeks only.
79 business days. 111 days contains 15 complete weeks, contributing 75 weekdays, and the remaining 6 days run Tuesday to Sunday, adding 4 more.
How the weekday count works, and what it misses
The counter walks the calendar one day at a time from the start date, stopping before the end date, and adds one for every day that is not a Saturday or Sunday. The start date is included and the end date is not, which is the standard way to count elapsed working days.
Public holidays are not deducted, and that is a real limitation rather than a detail. In the example above, Good Friday on 3 April 2026 and Easter Monday on 6 April 2026 both fall on weekdays and are both counted as working days. Anzac Day in 2026 falls on a Saturday, so it happens not to affect the count that year.
Holidays differ by state as well as by country. If you are working to a contractual deadline expressed in business days, take the figure here and subtract the gazetted holidays for your own state.
The month rollover trap in add and subtract mode
Adding or subtracting days, weeks and years behaves the way you expect. Months do not always, and this is the single most misunderstood thing about date arithmetic.
Adding one month to 31 January 2026 does not return 28 February. It returns 3 March 2026. The calculation sets the month forward while keeping the day number 31, and since February has only 28 days that year, the date overflows into March by three days.
The same thing happens adding one month to 31 August, which returns 1 October rather than 30 September. This is standard JavaScript date behaviour and it is what this tool does. Some other calculators clamp to the last day of the target month instead, which is why you may see different answers.
The practical takeaway: if you are calculating a deadline from a month-end date, check the result rather than assuming, or express the period in days instead.
Where this gets used
Invoice terms are the most common reason people land here. Net 30 and net 14 are counted in calendar days, not working days, so use the total days figure or the add mode rather than the business day card.
Notice periods, probation end dates and contract terms usually run in calendar weeks or months, which the first mode handles directly. Project scheduling and service level agreements more often run in working days, which is what the third card is for.
Travel and visa stays are another one. A permitted stay of 90 days is a calendar day count, so enter your arrival and departure dates and read the total days figure.
Things the tool does not do
Times of day are ignored. Every calculation reduces both ends to a plain calendar date, so a difference is never expressed in hours or minutes. Time zones are not applied either, which matters if you are counting across a change in local date.
If you enter an end date earlier than the start date, the tool swaps them and flags that it has done so rather than returning a negative number.
Related tools on ZillaKit
To measure from a birth date and get a birthday countdown as well, use the Age Calculator. For converting a date to or from epoch seconds, there is the Unix Timestamp Converter. If the working days you are counting need to be turned into billable hours, the Timesheet Generator handles that, and our guide to invoicing basics for Australian sole traders covers how payment terms are usually written.
Questions
Does the business day count include the start and end dates?
It includes the start date and excludes the end date. Counting from a Monday to the following Monday returns 5, not 6, because the final Monday is treated as the boundary rather than a day worked.
Why do the months and days not equal the total days divided by 30?
Because calendar months are not 30 days. The breakdown borrows the true length of the preceding month when the day number goes negative, so the two figures describe the same gap in two different units and will never line up neatly.
Can I count only certain weekdays, or exclude holidays?
No. The weekday filter is fixed to Monday through Friday and there is no holiday list. Both would need to be region specific to be accurate.
What does the reversed dates note mean?
It appears when your end date sits before your start date. The tool measures the gap anyway, from the earlier date to the later one, and tells you it has reordered them.
Is anything sent over the network?
No. Nothing you enter leaves the page; the maths happens on your device and no dates are stored between visits.