Choose the calculation
Decide whether you need a pure date difference, an inclusive milestone, business days, age, or time-zone conversion.
CATEGORY TOOLS
10045LIVE
Date Difference Calculator
Calculate exact days and calendar duration between two dates, with optional start-date inclusion plus weekday and weekend counts.
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046LIVE
Date Add & Subtract Calculator
Add or subtract days, weeks, months, or years from a date and see the resulting date and weekday.
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047LIVE
D-Day & Anniversary Calculator
Calculate D-Day, elapsed days, the next birthday, and 100-day or yearly anniversary milestones.
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048LIVE
Age & Elapsed Life Calculator
Calculate calendar age, year age, days since birth, and time until the next birthday from a birth date and as-of date.
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049LIVE
Employment Tenure & Service Period Calculator
Calculate employment tenure in years, months and days and add multiple employment periods.
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050LIVE
Business Days Calculator
Calculate business days between dates or find a date before or after N business days with weekend and holiday exclusions for Korea, the United States, and Japan.
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051LIVE
Time Calculator
Add or subtract time, calculate time differences across midnight, and convert between 12-hour and 24-hour formats.
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052LIVE
World Time & Timezone Converter
Compare UTC and multiple city times, convert with DST-aware IANA time zones, and find shared meeting hours.
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053LIVE
Unix Timestamp Converter
Convert Unix timestamps to dates and dates to seconds or milliseconds while comparing UTC and local time.
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054LIVE
Timer & Stopwatch
Use a countdown, stopwatch with lap and split records, and a Work/Rest repeat timer in your browser.
OPEN TOOL↗
HOW TO USE
How to use date and time tools
Choose the correct rule first for date differences, D-Day, age, business days, world time, or timers.Check dates and region
Confirm year, month, and day inputs; for world time check the location and time zone, and for business days check the holiday basis.
Verify the counting rule
Review inclusive or exclusive counting, leap-year and month-end handling, and time-zone differences before using the result.
EXPERT CATEGORY GUIDE
Why date and time calculations need clear rules
Date calculations look like simple subtraction, but inclusive counting, leap years, business days, and time zones can change the result. Define the rule that matches the task first.Inclusive counting
A pure difference between two dates can differ by one day from an anniversary count that treats the start date as day one. Check the tool's rule.
Leap years and month lengths
February 29 and month-end dates cannot be handled with a fixed 30-day month assumption. Calendar calculations need actual year, month, and day rules.
D-Day and anniversaries
D-Day usually expresses distance from a target date, while milestones such as the 100th day may count the start date. Use the rule that matches the purpose.
Business days
Business-day results depend on weekends, national holidays, and sometimes company-specific closures. Verify critical schedules against the real work calendar.
Time zones and world time
The same instant can have different local dates and times. For international schedules, check UTC offsets and daylight-saving rules.
Expressing periods
One month is not a fixed number of days. Contracts, tenure, and age calculations may need calendar years and months rather than a simple day count.
CATEGORY FAQ
Date & Time FAQs
01What tools are included in this category?+
This page collects the currently available tools related to Date & Time, and each one can be opened directly.
02Are all tools in this category free?+
The basic tools currently provided are free to use.
03Can I use them without an account?+
Yes. You can open each tool directly without registration.
04Can I use these tools on mobile devices?+
Yes. The pages adapt to phones and tablets.