Topical hub
Free Date & Time Calculators
Durations, business days, countdowns and time-unit arithmetic.
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Date and time arithmetic looks trivial until leap years, month lengths, weekends and time zones enter the calculation. These tools apply calendar rules consistently so a duration you compute today matches the one a payroll system or contract clock produces.
Three question types dominate. How long is it between two points? What date falls a given number of units from a reference? And how much working time does a span actually contain once weekends and holidays are removed?
Business-day logic is the most common source of disagreement. A ten-day contractual notice period may mean calendar days or working days, and the difference is typically four days. The tools here separate the two explicitly.
Time-unit conversion — decimal hours to hours and minutes, elapsed time between timestamps, timesheet totals — matters most in payroll and billing, where rounding conventions change what gets invoiced.
Age, countdown and calendar tools apply the same engine to personal timelines: age in years, months and days, days remaining to a milestone, or which weekday a historical date fell on.
Calculator directory
Date Differences & Durations
Measuring the span between two dates.
Free Age Calculator
Exact age in years, months, and days between two dates.
Free Date Calculator
Add or subtract days from a date, or find days between two dates.
Free Age in Days and Hours Calculator
Exact age expressed in days, hours and minutes.
Free Business Days Calculator
Count weekdays (Mon–Fri) between two dates.
Free Countdown to Date Calculator
Time remaining until a future date and time.
Free Days Between Dates Calculator
Exact number of days separating two calendar dates.
Free Elapsed Time Calculator
Duration between two clock times on the same day.
Free Months Between Dates Calculator
Calendar months and days separating two dates.
Free Project Deadline Calculator
Deadline date given a start date and business-day duration.
Free Retirement Date Calculator
Estimated calendar date you reach retirement age.
Free School Days Remaining Calculator
Weekday school days left until the last day of term.
Free Weeks Between Dates Calculator
Full weeks and remaining days between two dates.
Free Workdays From a Date Calculator
Find the date N business days after a start date.
Date Arithmetic & Calendars
Adding to or classifying a date.
Free Add or Subtract Days Calculator
Shift a date forward or backward by a number of days.
Free Chinese Zodiac Calculator
Chinese zodiac animal and element from a birth year.
Free Day of the Week Finder
Find which day of the week any date falls on.
Free Generation Finder Calculator
Which named generation a birth year belongs to.
Free Leap Year Calculator
Check whether a year is a leap year.
Free Fiscal Quarter Finder
Which calendar or fiscal quarter a date falls in.
Free Week Number Calculator
ISO 8601 week number for a given date.
Free Zodiac Sign Calculator
Western astrological sign from a birth date.
Time Tracking & Conversion
Hours, timesheets and unit conversion.
Free Hours Calculator
Hours and minutes between a start and end time, minus break.
Free Time Calculator
Add or subtract hours, minutes, and seconds.
Free Decimal Hours Converter
Convert between HH:MM time and decimal hours.
Free Meeting Time Planner
Local meeting time for a remote participant given a UTC offset gap.
Free Military Time Converter
Convert between 12-hour and 24-hour clock time.
Free Weekly Time Card Calculator
Total weekly hours from five daily clock-in/out pairs.
Free Time Duration Adder
Add two durations given in hours, minutes and seconds.
Free Time Zone Difference Calculator
Hour difference between two fixed UTC offsets.
Key concepts in date & time calculators
- Duration
- The elapsed span between two instants, expressed in a chosen unit.
- Calendar day
- Every day counted, weekends and holidays included.
- Business day
- Weekdays excluding public holidays, the default for contractual and payroll clocks.
- Leap year
- A year divisible by 4, except centuries not divisible by 400 — the reason naive day counts drift.
- Inclusive counting
- Whether the start and end dates are both counted, which changes the result by one day.
- Decimal hours
- Time expressed as a fraction of an hour (7.5 = 7h 30m), used in timesheets and billing.
How this topic works
Why day counts disagree
Two systems can report different day counts for the same span because of inclusive versus exclusive endpoints. Counting from Monday to Friday gives four days exclusively and five inclusively. Contracts, hospital stays and rental agreements each use their own convention, so state the convention before comparing outputs.
Business days and holiday calendars
Business-day calculations remove Saturdays and Sundays, then subtract any public holidays that fall on a weekday. Because holiday calendars are jurisdiction-specific, the same 30-business-day window can end on different dates in different countries. Always confirm which calendar governs the deadline.
Age and anniversary arithmetic
Age in years, months and days is computed by borrowing across month boundaries, which is why the answer depends on the length of the intervening months. A person born on 31 January has no anniversary date in February, so systems apply either the 28th/29th or 1 March, another common source of off-by-one differences.
Timesheets, rounding and payroll
Payroll systems often round clock entries to the nearest 6, 10 or 15 minutes. Rounded to the nearest quarter hour, a 7-minute overrun disappears while an 8-minute one becomes 15 minutes. Decimal-hour conversion and elapsed-time tools keep the raw figure visible so rounding is a deliberate step rather than a hidden one.
Frequently asked questions
How do I count business days between two dates?
Remove weekend days from the span, then subtract public holidays that fall on weekdays. The business days calculator applies both steps for you.
Should the start date be included in a duration?
It depends on the convention. Inclusive counting includes both endpoints and adds one day to the exclusive result — check which one your contract or policy specifies.
How is age calculated exactly?
Age is derived by subtracting years, then months, then days, borrowing across month boundaries when the day component is negative, which accounts for varying month lengths and leap years.
What is a decimal hour?
A decimal hour expresses minutes as a fraction of an hour: 90 minutes is 1.5 decimal hours. Payroll and billing systems typically require this format.
Do these tools account for leap years?
Yes. Day counts, age and add-subtract-days calculations use full calendar rules including leap years.
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