How to use the date calculator
- Choose Add or subtract to move forward or back from a date, or Between two dates to compare two dates.
- In Add or subtract, pick a start date, whether to add or subtract, and either years/months/weeks/days or a number of business days only (Monday-Friday).
- In Between two dates, enter a start and end date. Tick Include the end date to count both the first and last day (for example, when counting nights of a stay vs. days present).
- Read the result date or day count, plus the day of the week, ISO week number, and (between two dates) the weeks, business days and weekend days.
How to count the days between two dates
Convert each date to a running day count (days since a fixed point) and subtract the earlier from the later. From Jan 1, 2025 to Sep 26, 2026:
- Exact calendar difference: 1 year, 8 months, 25 days
- Total days: 633 days
- Weeks and days: 90 weeks, 3 days
Tick include the end date if you want both the start day and the end day counted (this adds exactly one day to every total above).
30 days from today: a reference table
This table is generated from Sep 26, 2026, the date this page was last rebuilt, so the dates below are a worked example rather than today's real date. The calculator above fills in your browser's actual today automatically -- open it and switch to "Add or subtract" for a live answer.
| Days from Sep 26, 2026 | Date | Day of week |
|---|---|---|
| 7 days | Oct 3, 2026 | Saturday |
| 14 days | Oct 10, 2026 | Saturday |
| 15 days | Oct 11, 2026 | Sunday |
| 30 days | Oct 26, 2026 | Monday |
| 45 days | Nov 10, 2026 | Tuesday |
| 60 days | Nov 25, 2026 | Wednesday |
| 90 days | Dec 25, 2026 | Friday |
| 100 days | Jan 4, 2027 | Monday |
| 180 days | Mar 25, 2027 | Thursday |
| 365 days | Sep 26, 2027 | Sunday |
Business (working) days between two dates
A business day calculator counts only Monday through Friday, leaving out Saturdays and Sundays (and any holidays you know to subtract yourself -- this calculator does not know regional holidays). Over the two full weeks from Sep 28, 2026 to Oct 11, 2026 (including both ends, 14 days in total):
- Business days: 10
- Weekend days: 4
To add business days to a date instead of counting them between two dates, use "Add or subtract" mode and choose "Business days only": it skips weekends entirely, so adding 10 business days to a Friday lands 2 full weekends later.
Leap years and month lengths
A year is a leap year (366 days, with 29 days in February) if it divides evenly by 4 -- except a century year (ending in 00), which must divide evenly by 400 as well. So 2024 is, 2025 is not, 1900 is not, 2000 is a leap year. This matters most when adding months: Jan 31, 2026 + 1 month = Saturday, Feb 28, 2026 (2026's February has 28 days), while Jan 31, 2024 + 1 month = Thursday, Feb 29, 2024 (2024 is a leap year). The calculator always clamps to the last real day of the target month rather than overflowing into the month after.
ISO week numbers
Alongside every result, the calculator shows the ISO-8601 week number: weeks run Monday to Sunday, and week 1 is the week containing the year's first Thursday. Sep 26, 2026 is in week 39 of 2026.
More work-hours tools
- Hours calculator: the hours and minutes between two clock times, minus breaks.
- Time card calculator: add up a weekly timesheet with breaks, overtime and pay.
- Clock out time calculator: what time you'll clock out from a start time and hours worked.
Frequently asked questions
How do I calculate the number of days between two dates?
Convert both dates to a day count and subtract: end day − start day. From Jan 1, 2025 to Sep 26, 2026 is 1 year, 8 months, 25 days, or 633 days in total. The calculator's "Between two dates" mode does this for any two dates, with an option to also count the end date.
How do I add days to a date?
Add the number of days to the date's day count and convert back to a calendar date. Jan 1, 2026 plus 30 days is Saturday, Jan 31, 2026. Switch to "Add or subtract" mode, enter a start date and the days (or weeks, months, years) to add, and the calculator handles month lengths and leap years automatically.
How do I find a date a number of days from today?
Use "Add or subtract" mode with today as the start date. As an example computed from Sep 26, 2026 (this page's last-reviewed date): 30 days later is Monday, Oct 26, 2026, a Monday. Open the calculator above, which fills in today's actual date automatically.
How do I count business days between two dates?
Count only Monday-to-Friday dates in the range; weekends don't count. Over the two full weeks from Sep 28, 2026 to Oct 11, 2026 (14 days including both ends) there are 10 business days and 4 weekend days. The calculator shows this split for any range, and "Add or subtract" mode can also add a number of business days to a date, skipping weekends.
How does adding a month work when the day doesn't exist in the new month?
The day is clamped to the last day of the new month. Jan 31, 2026 plus 1 month is Saturday, Feb 28, 2026 (February only has 28 days in 2026), while Jan 31, 2024 plus 1 month is Thursday, Feb 29, 2024, because 2024 is a leap year.
What years are leap years?
A year is a leap year if it divides evenly by 4, except century years, which must divide evenly by 400. So 2024 is, 2025 is not, 1900 is not, 2000 is a leap year. Leap years have 29 days in February and 366 days in total; the calculator accounts for this automatically in every calculation.
Does this calculator handle time zones or daylight saving time?
The date calculator works with calendar dates only (no clock time), calculated in UTC internally, so daylight saving changes never shift a result by an hour or a day. If you need the time between two clock times instead, use the hours calculator or time calculator.
What is a week number?
The ISO-8601 week number (1-53) counts full Monday-to-Sunday weeks in a year, with week 1 being the week that contains the year's first Thursday. Sep 26, 2026 falls in ISO week 39. The calculator shows the week number for every result date.
What happens if the end date is before the start date?
The calculator still works: it measures the gap between the two dates and says so, rather than showing a negative number. Enter the dates in either order in "Between two dates" mode.
Is my data saved or sent anywhere?
Your entries are saved only in your own browser so they are there next time. Nothing is sent to our servers.