Date calculator: days between dates, add days to a date

Give two dates and get the days between them, also in weeks, in years, months and days, and in working days. Or give one date and a duration in days, working days, weeks, months or years, and get the date it lands on, with its weekday, its ISO week, and the nearest working day when it falls on a weekend. Free, no account, nothing stored.

What it does, and why it is here

Counting days goes wrong in three places: whether the last day counts, how many days a month has, and where the weekends fall. A 45-day payment term, a notice period, a delivery in ten working days: each looks simple and ends up a day or two off when counted on a wall calendar.

This calculator turns each of those choices into a field you can see — the end day, the unit, the end of the month — so the answer says what it counted. I would rather a date tool show its convention than hide a good guess.

What you fill in

What to calculate picks the question: Days between two dates (the default) or Add to a date. Each reads its own fields.

• From — the date counted from, for both questions, opening on today’s date. Any date from the year 1583 to 9999, on the Gregorian calendar.

For Days between two dates:

• To — the date counted to. It may be earlier than From: the answer is then negative.
• Count the end date too — unticked by default, so the count runs from the From date up to, but not including, the To date: 4 days from a Monday to the Friday of the same week. Tick it for an inclusive count, the one a leave or a period “from … to … inclusive” uses: 5 days.

For Add to a date:

• How many and Of — the amount, 30 by default, and its unit: days, working days (Mon–Fri), weeks, months or years. The amount runs from 0 up to 100,000 days, 20,000 working days, 10,000 weeks, 1,200 months or 100 years. A month or a year later is the same day number, or the last day of a shorter month: January 31 plus one month is February 28, or February 29 in a leap year. Working days skip Saturdays and Sundays, and the From date itself is never one of them: 10 working days after a Saturday is the second Friday after it.
• Count backwards (before the date) — subtracts instead: 10 working days before a deadline, 6 weeks before an event.
• Then go to the end of that month — once the amount is added, moves to the last day of the month it lands in. This is the “30 days end of month” of a payment term: an invoice dated October 15 plus 30 days is November 14, and the end of that month is November 30.
• What this date is — optional, 80 characters at most: Invoice due, Notice ends. It heads the answer and names the calendar event.

What you get back

Between two dates, the number of days leads, followed by the same stretch three other ways:

• In weeks — whole weeks and the days left over: 255 days is 36 wk 3 d.
• In years, months, days — the way an age or a length of service is told: from May 12, 1990 to September 27, 2026 is 36 y 4 mo 15 d.
• Working days — the Mondays to Fridays among the days counted, so the end date is one of them only when you ticked it. Public holidays are not deducted.

Added to a date, the date found leads, written out with its weekday (Tuesday, October 27, 2026) under the name you gave it, followed by:

• Calendar days — the days from the From date to the date found, negative when counting backwards. After an end of month, it is the real distance: 46 days for 30 days end of month from October 15.
• Working days — the Mondays to Fridays stepped over, after the From date up to and including the date found, so 10 working days added are 10 counted.
• ISO week — the week number of the date found, weeks starting on Monday as in ISO 8601. December 31, 2026 falls in week 53.
• The weekend notice — when the date found is a Saturday or a Sunday, a line names the next working day: This falls on a weekend: the next working day is Monday, November 16, 2026. Whether a deadline moves to that Monday depends on your contract or your jurisdiction.

Under a date found, one more thing appears only after you compute: Add to my calendar downloads a calendar file (.ics) holding one all-day event on that date, named after What this date is, or Date to remember when you left it empty. Any calendar application opens it. A count between two dates offers none.

What it does not do

• It does not know public holidays: working days are Mondays to Fridays everywhere, one too many for each weekday holiday in the stretch.
• It does not move a date found on a weekend: it names the working day beside it — the Monday after when counting forward, the Friday before when counting back — and the date shown stays the one the count gives.
• It reads “30 days end of month” one way: add the days, then go to the end of that month. If your terms mean the end of the invoice month first, then 30 days, set From to that last day and add 30 days, box unticked.
• It counts whole calendar days: no hours, no time zones.

Common payment terms from one invoice date

Due dates for an invoice dated Thursday, October 15, 2026, each computed here with Add to a date.

Net 30 and one month differ by a day, 30 and 45 days end of month coincide for a mid-month invoice, and four of the ten dates fall on a weekend.

Questions

How many days are there between two dates?

Choose Days between two dates, enter both, and read the number at the top of the answer.

Does the date calculator include the end date?

Not by default: from a Monday to the Friday of the same week is 4 days, the difference between the two dates. Tick Count the end date too and it is 5.

How do I add working days to a date?

Choose Add to a date, enter the number and pick working days (Mon–Fri): the start date is not counted, Saturdays and Sundays are skipped, and public holidays are not.

What does “30 days end of month” mean?

It means adding 30 days to the invoice date, then going to the last day of that month: October 15 gives November 14, then November 30. Tick Then go to the end of that month to get it.

Can I add the date to my calendar?

Yes: after Add to a date, Add to my calendar downloads an .ics file with an all-day event on the date found.

Is it free, and is anything stored?

It is free, needs no account, and the dates are computed and forgotten.

Sources and further reading

• Net D — net 30, net 60 and early-payment discounts such as 2/10 net 30.
• ISO week date — how week numbers are counted, and why some years have a week 53.
• RFC 5545 — the iCalendar format of the .ics file.