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Date & Time Calculators

Age, day counts, date offsets, weekdays, business days, clock durations, and work hours using explicit calendar rules.

Calendar and clock math: age calculators, days between dates, date addition, weekday and business-day counts, time durations, work hours with breaks, and pregnancy due dates — with stated endpoint, holiday, elapsed-versus-inclusive, and UTC conventions.

15 free tools · each with formula, worked example & methodology notes

Category context

The calendar conventions behind the answer

Date and time results depend on endpoints, elapsed versus inclusive counting, weekends, supplied holidays, and whether time zones are included.

Method and background

Calendar arithmetic translates dates and clock readings into durations and schedules. It is separate from local operating policy or a live calendar service, so the page states what it does and does not count.

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Calculator directory

Choose the tool that matches your question

15 tools arranged by purpose, so you can scan the right group before opening a calculator.

3 tools

Ages and milestones

Age between dates, completed years and days, and life-event calculations.

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Birth Date from Death Date and Exact Age Calculator

Work backward from a death date and an entered completed age in years, months, and days using explicit Gregorian calendar arithmetic for genealogy and historical records.

You enter: Death date · Completed age — years · Completed age — additional months · Completed age — additional days

Example: The calculated birth date is 1926-04-21 under the Gregorian calendar subtraction convention.

Open Birth Date from Death Date and Exact Age Calculator →

5 tools

Calendar dates

Date differences, adding days, weekdays, palindrome dates, and calendar planning.

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Business Days Calculator

Count weekdays between two dates with explicit endpoint rules and your own holiday list.

You enter: Start date · End date · Include start date · Include end date · Holidays to exclude (optional)

Example: 22 business weekdays across 31 calendar days.

Open Business Days Calculator →

Palindrome Date Checker

Check whether a date reads the same forward and backward in a selected numeric format and search for the next matching date.

You enter: Date · Numeric date format · Forward search limit

Example: 20011002 is a palindrome in YYYYMMDD order, so the entered date is marked as a match.

Open Palindrome Date Checker →

5 tools

Clock time and work

Time zones, durations, counted hours, breaks, and working-time estimates.

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Add Time Durations Calculator

Add two durations and normalize the total into days, hours, minutes, and seconds without wrapping at midnight.

You enter: First duration hours · First duration minutes · First duration seconds · Second duration hours · Second duration minutes · Second duration seconds

Example: Total = 4 hours, 16 minutes, 15 seconds (15,375 seconds).

Open Add Time Durations Calculator →

Time Zone Offset Converter

Convert a date and time between two fixed UTC offsets without pretending to know city daylight-saving rules.

You enter: Source date · Source time · Source UTC offset · Target UTC offset

Example: 12:00 UTC converts to 17:30 at UTC+5.5 on the same date.

Open Time Zone Offset Converter →

2 tools

Fertility and pregnancy dates

Fertile-window and due-date estimates with clearly stated calendar conventions.

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Calculator usage statistics

Most-used Date & Time Calculators tools

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How to use these tools

Each calculator shows its formula, assumptions, and a worked example. Enter your values, choose Calculate, and copy results for reports or planning. Financial and health tools are planning estimates with stated limits, not professional advice.

Frequently asked questions

What is the difference between elapsed and inclusive day counts?

Elapsed days exclude the start date, so a same-date interval is zero. Inclusive days count both endpoints, so a same-date interval is one day.

Are time zones or daylight saving applied?

No time-zone or daylight-saving conversion is applied. Calendar tools use UTC midnight; business days exclude Saturday and Sunday plus only the holiday dates you enter.