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Time & Date tool map

Dates & calendars

Dates, weekdays, ages, and calendar intervals.

Choose the tool whose inputs and output match your task. Check each calculator’s assumptions and limitations before using its result.

Latest update:

Dates and calendars bring their own arithmetic: months vary in length, leap years add February 29, and one span reads differently as a day count or a years-months-days breakdown. Use the age calculator to find completed years, months, and days from a birth date to any chosen date. The date duration calculator breaks any span into full years, months, and days next to an exact total-day count — handy for contract terms and milestones. When the working calendar matters, the business days between dates calculator counts weekdays and removes your holiday list, and the ISO week number calculator turns any date into its ISO week and week-year for reporting. More tools await in the Time & Date collection.

9 of 9 calculators

Dates & calendars9 calculators

Age Calculator

Popular

Calculate exact age in years, months, and days from a birth date to any age-at date, plus total months, weeks, days, weekday born, and next birthday.

Updated

Verified

Business Days Between Dates Calculator

Count business days between two dates, excluding weekends and any holidays you add, with calendar days, weekends, and full weeks.

Updated

Verified

Date Duration Calculator

Calculate the duration between two dates as full years, months, and days, plus the exact total days, months, and weeks.

Updated

Verified

Gestational Age Calculator

Estimate gestational age in weeks and days, due date, trimester, conception date, milestones, and prenatal timing from LMP, conception, or ultrasound dating.

Updated

Verified

ISO Week Number Calculator

Find the ISO 8601 week number and week-year for any date, using the Thursday rule, with weekday name and ISO week date.

Updated

Verified

Julian Date Converter (JD, MJD, RJD, TJD)

Convert dates to Julian Date (JD), Modified Julian Date (MJD), Reduced Julian Date (RJD), and Truncated Julian Date (TJD), or convert a Julian Date back to UTC.

Updated

Verified

Pregnancy Conception Calculator

Estimate a likely conception date, possible conception range, and due date from an estimated due date, last period, cycle length, or ultrasound dating.

Updated

Verified

Reverse Due Date Calculator

Work backward from a pregnancy due date to estimate last menstrual period, likely conception timing, trimester boundaries, milestones, and appointment windows.

Updated

Verified

Time Card Calculator

Calculate weekly time card hours, regular hours, overtime hours, and unpaid lunch deductions for selected workdays.

Updated

Verified

Frequently asked questions

How do I calculate my exact age?
Enter the date of birth and the age at date. The calculator checks that the birth date is not after the age-at date, then counts completed calendar years, remaining months, and remaining days. It also reports total months, weeks, days, weekday born, and days until the next birthday.
Why is exact age not just current year minus birth year?
Year subtraction ignores whether the birthday has happened yet. Someone born in December is not one year older in January just because the calendar year changed. This calculator compares month and day, borrows from the previous month when needed, and returns the leftover calendar months and days.
Can this calculate age on a past or future date?
Yes. Change the age at date to any valid date on or after the birth date. That lets you answer questions such as how old someone was on an event date, how old a child will be at a school cutoff, or how many days old someone is today.

More in Time & Date

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Related comparisons

All Time & Date comparisons →
Age Calculator vs Date Duration CalculatorCompare years, months, and days since a birth date with next-birthday countdown against the duration between any two dates with exact day counts.Age Calculator vs Gestational Age CalculatorCompare the age calculator's completed years, months, and days from a date of birth with the gestational age calculator's weeks and days from a pregnancy dating start: birthday age versus pregnancy dating.Age Difference vs Date DurationCompare the age difference calculator's three methods for the gap between two ages, birth years, or birth dates with the date duration calculator's calendar breakdown and exact day count.Age vs Age DifferenceCompare the age calculator's exact calendar age for one person with the age difference calculator's gap between two people, ages, or birth years: birthday-aware arithmetic versus an absolute gap with approximate and precise methods.Age vs Business Days Between DatesCompare calendar age in years, months, and days since a birth date with the Monday-to-Friday working-day count between two dates, and when each span convention applies.Age vs Time DurationChoose between a calendar-age calculator that breaks a birth date to any date into years, months, and days with a next-birthday countdown, and a clock calculator that measures or shifts intervals between times of day.Business Days Between Dates vs Date DurationCompare counting Monday–Friday working days with holiday exclusions against breaking any calendar span into years, months, days, and exact total days.Business Days Between Dates vs ISO Week NumberCompare counting the Monday-to-Friday working days between two dates for deadlines and notice periods with finding the ISO 8601 week number of a single date for week-based reporting and planning.Business Days Between Dates vs Time DurationCompare counting Monday-to-Friday working days between calendar dates, with holidays excluded, and measuring elapsed clock time between times of day, with totals in hours, minutes, and seconds.Gestational Age vs Pregnancy ConceptionCompare two pregnancy dating tools: current gestational age in weeks and days with trimester and milestones versus a likely conception date with a possible range, from the same dating methods.Gestational Age vs Pregnancy Due DateCompare pregnancy dating tools: one reports how far along a pregnancy is in weeks and days, the other centers on the estimated due date — and when to use each.ISO Week Number vs Julian DateCompare two date-numbering schemes: the ISO 8601 week number with week-year for week-based reporting versus the continuous astronomical Julian Day count for science and operations.Julian Date vs Date DurationChoose between astronomical Julian Date conversion for continuous day counts and a calendar duration calculator that breaks spans into years, months, and days.Pregnancy Due Date vs Conception CalculatorCompare pregnancy due date and conception calculators: one estimates the delivery date from last menstrual period or conception date, the other works backward from a due date, last period, cycle length, or ultrasound to a conception window.Reverse Due Date vs Gestational AgeCompare the two directions of pregnancy dating: working backward from a due date to LMP, conception, and milestones versus counting forward from LMP, conception, or ultrasound to gestational age.Reverse Due Date vs Pregnancy ConceptionCompare the reverse due date and pregnancy conception calculators: a full backward pregnancy timeline from a due date versus a conception-date estimate and range from due date, last period, or ultrasound.Reverse Due Date vs Pregnancy Due DateCompare the reverse due date and pregnancy due date calculators: working backward from a due date to LMP and conception versus estimating a due date from LMP or conception date.Shift Calculator vs Time Card CalculatorChoose between a single-shift start and end time planner with unpaid breaks, and a weekly timesheet that totals regular and overtime hours across selected workdays.Time Duration vs Date DurationCompare the time duration calculator's clock-interval math with the date duration calculator's calendar span: hours, minutes, and seconds versus years, months, days, and exact day counts.Time Duration vs Time Card CalculatorCompare measuring a single clock interval in hours, minutes, and seconds against totaling weekly work hours with lunch deductions and overtime.Unix Time vs Julian Date ConverterCompare Unix time and Julian Date: two ways to represent a moment as a single number — and which one your logs, APIs, or astronomy records should use.

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