What this date calculator does
You can use this page in two ways. The first mode measures the time between two dates. The second mode moves a date forward or backward by years, months, weeks and days. Both modes run on the same rule: every day is 24 hours. Daylight saving changes are not counted, so a day never has 23 or 25 hours here.
The difference between two dates is a subtraction, not a count of both ends. Monday to Friday is 4 days. If you need to include both the start and the end date, turn on the inclusive option. That adds one day to the result. This is the same rule used by the business days calculator, which skips weekends and any holiday dates you list.
Days between two dates
Type a start date and an end date. The tool returns the gap in days, weeks, months and days, and years. It also shows the total in days and the total in weeks.
Here is a worked example. Start date: January 31, 2026. End date: March 1, 2026. The result is 1 month and 1 day, or 29 days in total. January 31 plus one calendar month lands on February 28, 2026, because 2026 is not a leap year. From February 28 to March 1 is one more day.
Leap years matter for long gaps. A leap year happens every 4 years, except century years that are not divisible by 400. So 2024 and 2028 are leap years, and 2100 is not. February 29 exists only in a leap year. If you count a birthday or an anniversary across a leap year, the extra day shows up in the total.
You can also ask for the days from today. Today is September 16, 2026. The tool uses your device's current date, so the answer updates as the date changes.
Add or subtract days, weeks, months and years
The second mode takes one date and shifts it. You choose how many years, months, weeks and days to add or subtract. The tool applies the largest unit first, then the smaller ones.
Months are calendar months, not fixed blocks of 30 days. This is where end-of-month rules show up. January 31 plus one month is February 28 in a normal year, or February 29 in a leap year. The tool clamps to the last valid day of the target month instead of rolling into the next month.
Weeks are always 7 days. Years are calendar years, so February 29 plus one year becomes February 28 in a non-leap year. Days are plain 24-hour days.
If you want to know how old someone is in whole years, months and days, the age calculator uses the same calendar rules. A February 29 birthday falls on March 1 in a non-leap year for the next-birthday countdown.
Common questions about date math
Is the end date counted?
No. The default result is the difference between the two dates. Monday to Friday is 4 days. The inclusive option adds one so both ends count.
How do months work?
Months are calendar months. January 31 plus one month is February 28, or February 29 in a leap year. January 31 to March 1 is 1 month and 1 day.
Do leap years change the answer?
Yes, for gaps that cross February 29. Leap years are every 4 years, except century years not divisible by 400. 2024 and 2028 are leap years. 2100 is not.
Does daylight saving change a day?
No. Every day here is 24 hours. A clock change does not make a day 23 or 25 hours in this tool.
What about business days?
Business days are Monday to Friday. Saturdays and Sundays are skipped, plus any holiday dates you list. The start day itself is not counted. There is no built-in national holiday list, because holidays differ by country, region and employer. Use the business days calculator for that.
How the date math stays honest
The calculator works from your device's clock and calendar. It does not count ticks, so it stays correct when the tab is in the background or the device sleeps. The display refreshes several times a second.
You can type durations in several ways: 5 for seconds, 5:00 for minutes and seconds, 1:30:00 for hours, minutes and seconds, or 90m, 1h 30m, 2d 3h. Clock times work as 9:00, 9:00 am, 17:30 or 1730.
If you need to convert between time zones, the time zone converter uses the browser's built-in zone database. Zone names like America/New_York are more reliable than abbreviations like EST or EDT, because a place can switch between them.
For plain time arithmetic, remember that 1.5 hours is 1:30, not 1:50. Decimal hours equal minutes divided by 60, so 7:30 is 7.5 hours and 0:45 is 0.75 hours. The time calculator handles those sums.