Free Online Date and Time Tools
Work with dates, durations, timestamps and time zones using practical online tools. Calculate the days between dates, estimate an age from a date of birth, check leap years or prepare time values for scheduling and development tasks.
Date calculations can depend on calendar rules, local time and the way a tool counts intervals. Choose the relevant utility and check its assumptions before relying on the result for an important deadline or schedule.
Date Calculators, Time Converters and Calendar Utilities
Choose a tool based on whether you are comparing dates, working with clock times or converting a timestamp. Each individual tool should clearly explain the required inputs and the result it returns.
Date Difference Calculator
Calculate the interval between two dates and check whether the result represents elapsed days or an inclusive calendar-day count.
Open tool →Days Between Dates
Count days between a start date and end date for project planning, event preparation or general date comparisons.
Open tool →Age Calculator
Calculate age in years, months and days using a date of birth and a selected reference date.
Open tool →Leap Year Calculator
Check whether a year has 365 or 366 days using the Gregorian calendar leap-year rules.
Open tool →Add Days to a Date
Find a future or past date by adding a positive or negative number of calendar days to a starting date.
Open tool →Business Days Calculator
Estimate working days between dates using the selected weekend rules and any supported holiday settings.
Open tool →Time Duration Calculator
Calculate the elapsed duration between two times, including supported overnight intervals.
Open tool →Hours Calculator
Add or subtract hours and minutes to help work out durations for schedules, timesheets and planning.
Open tool →Time Zone Converter
Convert a specified date and time between supported time zones while accounting for applicable local offset rules.
Open tool →UTC to Local Time Converter
Convert a UTC date and time into a selected local time zone, including the applicable offset for that date.
Open tool →Unix Timestamp Converter
Convert Unix timestamps to readable dates or convert supported dates into timestamps. Check whether input uses seconds or milliseconds.
Open tool →Countdown Calculator
Calculate the remaining interval until a selected date or event using a clearly specified reference time.
Open tool →Date to Timestamp Converter
Convert a supported date and time into a timestamp while specifying the correct time zone and timestamp unit.
Open tool →Day of the Week Calculator
Find which weekday corresponds to a calendar date using the selected calendar system.
Open tool →Week Number Calculator
Find a date’s week number and check which week-numbering convention is used.
Open tool →Date Format Converter
Reformat supported date values into a chosen display format, with care around ambiguous day and month ordering.
Open tool →Leap Years, Calendar Days and Date Differences
Calendar calculations follow defined rules. Understanding those rules helps explain why some years contain an extra day and why two different date counters can return different results.
How is a leap year determined?
Under the Gregorian calendar, a year is a leap year if it is divisible by 4, except that century years must also be divisible by 400.
- 2024 was a leap year because it is divisible by 4.
- 1900 was not a leap year because it is divisible by 100 but not 400.
- 2000 was a leap year because it is divisible by 400.
- A leap year has 366 days, including 29 February.
Elapsed days or inclusive dates?
These are different counting methods. The difference between 1 March and 3 March is two elapsed days. Counting both 1 March and 3 March as calendar dates gives three dates.
- Elapsed-day calculations measure the interval between dates.
- Inclusive counts include both the start and end date.
- Business-day counts may exclude weekends and selected holidays.
- Always check the method used for deadlines and schedules.
Understand UTC, Time Zones and Daylight Saving
A clock time alone may not identify one exact moment. A reliable time conversion also needs a date and an appropriate time zone.
| Term | What it means | What to check |
|---|---|---|
| UTC | Coordinated Universal Time, commonly used as a global reference for timestamps. | Confirm whether a timestamp is explicitly expressed in UTC. |
| UTC offset | The difference between a local clock time and UTC at a particular moment. | Offsets can change in locations that observe daylight saving. |
| Time zone | A regional set of civil-time rules, often represented by an IANA name such as Europe/London. | Use the appropriate named zone for the intended date. |
| Daylight saving time | A seasonal change in local clock time used in some regions. | Start and end dates vary by location and year; not every location observes it. |
| Unix timestamp | A numeric representation of time commonly measured in seconds or milliseconds from the Unix epoch. | Check the unit, time-zone interpretation and supported date range. |
How to Use Date and Time Tools Correctly
Follow these steps when calculating a date, comparing times or converting a timestamp.
Enter the complete value
Provide the relevant date, time, time zone and any other required inputs. Avoid ambiguous date formats.
Check the calculation method
Review whether the tool uses elapsed days, inclusive dates, business days, UTC or local civil time.
Verify important dates
Cross-check deadlines, travel schedules and appointments against an authoritative calendar or time-zone source.
Date & Time Tools FAQs
Learn more about date arithmetic, leap years and time conversion.
What are date and time tools used for?
They help calculate date differences, ages and durations, check leap years, convert timestamps, compare time zones and prepare dates for scheduling or software development.
How do I know if a year is a leap year?
In the Gregorian calendar, a year divisible by 4 is normally a leap year. Century years are exceptions unless they are divisible by 400. This rule determines whether February has 28 or 29 days.
Why do two date calculators show different day counts?
One may calculate elapsed days while another counts both the start and end dates. Business-day calculators may also exclude weekends or holidays. Check the counting convention before comparing results.
What is the difference between UTC and a time zone?
UTC is a global time reference. A time zone defines local civil-time rules for a region, which may include changing UTC offsets due to daylight saving.
Why can a time-zone conversion change depending on the date?
Some regions change their clocks seasonally. A location may have one UTC offset in winter and another in summer, so conversions should use the intended date and named time zone.
Does every country observe daylight saving time?
No. Many countries do not change their clocks seasonally. Others apply daylight-saving rules that can differ by region and year. Always check the selected location’s applicable rules.
What is a Unix timestamp?
A Unix timestamp represents time as a number relative to the Unix epoch, which began on 1 January 1970 at 00:00:00 UTC. Implementations commonly use seconds or milliseconds, so the unit matters.
Can I use a date calculator to confirm an official deadline?
Use it to estimate the date interval, then verify the deadline against the relevant organisation’s rules. Official deadlines may use specific business-day, public-holiday, local-time or inclusive-counting conventions.
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