Date & Time Tool
Date & Time Calculator
Calculate a date & time
Start from
years
months
weeks
days
Mix any units. Arrow keys step a value up or down.
Saturday, 19 September 2026
No offset applied — this is the start moment itself.
Weekday
Sat
Day of year
262 / 365
Week / Quarter
W38 · Q3
Relative
today
Formatted Output
ResultSaturday, 19 September 2026, 00:00:00
ISO 86012026-09-19T00:00:00.000Z
Unix (s)1789776000
Unix (ms)1789776000000
UTC (GMT)Sat, 19 Sep 2026 00:00:00 GMT
Component Breakdown
Year
2026
Month
Sep
Day
19
Hour
00
Minute
00
Second
00
Tool features
4 features
Add or subtract
Move forward or back by any mix of years, months, weeks, days, hours, minutes and seconds.
Date or date and time
Work with calendar dates alone, or include a time of day.
Every format
See the result as a readable date, ISO 8601, UTC and Unix time in seconds and milliseconds.
Calendar-aware
Month lengths and leap years are handled, so adding a month lands on the right day.
What is date arithmetic & how it works
Date arithmetic answers questions like "what date is 90 days from today?" or "what was the time 36 hours ago?". Adding days and hours is simple counting, but months and years vary in length, so adding one month to 31 January has to land on the last day of February.
This calculator applies each unit in calendar order and shows the result in several formats at once, including ISO 8601 and Unix time for use in code, configs and API calls.
ISO 8601
The unambiguous 2026-09-19T14:30:00Z format used by APIs.
Month overflow
Adding a month to a day that does not exist lands on the last valid day.
Unix time
Seconds (or milliseconds) since 1 January 1970 UTC.
How to use this tool
1
Pick a start
Choose the starting date, and a time of day if you need one.
2
Add or subtract
Choose whether to go forward or back in time.
3
Enter the amounts
Fill in any combination of years, months, weeks, days, hours, minutes and seconds.
4
Copy the result
Copy the resulting date as text, ISO 8601, UTC or a Unix timestamp.
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Frequently asked questions
5 Q&A
February has no 31st, so the result is the last day of February (28th, or 29th in a leap year).
No. A month moves to the same day in the next month, which can be 28 to 31 days later. Use days when you need an exact count.
Your browser’s local time zone for the input and readable result. The UTC and Unix outputs show the same moment in zone-free form.
Not here: every calendar day counts. Use the days-between-dates calculator to see how many weekdays a span contains.