Age Difference Calculator (Two Birth Dates)

From your date of birth, get exact age, Chinese nominal age (虛歲), days lived and days to next birthday.

Enter any two dates to get the calendar gap, working days, weekend days, plus year/month/day breakdown and total weeks/months.

Pick your local and target cities to convert a given clock time across time zones.

Add or subtract years, months, weeks and days from a start date to get the resulting date and weekday.

Count the working days between two dates (excluding weekends) — or add N business days to a start date to find the deadline.

Estimate the due date from your last menstrual period (LMP) using Naegele's rule, plus current gestational week, trimester and key pregnancy milestones.

Enter clock-in/clock-out times and break minutes to get total hours worked and gross pay — overnight (graveyard) shifts handled automatically.

Pick any date to see which day of the year (1–366), ISO 8601 week number, weekday, and how many days from the start and end of the year.

Enter any Gregorian date (past or future) to instantly find the day of the week — useful for birthdays, anniversaries and historical events.

Convert a Unix timestamp (seconds or milliseconds since 1970-01-01 UTC) to UTC, Hong Kong time and RFC 1123 HTTP date — and back. Built for debugging log files, API responses and database fields.

Pick a year and the Computus algorithm returns Easter Sunday plus Ash Wednesday, Palm Sunday and Good Friday.

Enter any date to compute the lunar phase (new, first quarter, full, last quarter …), moon age in days and illuminated fraction.

Find your Chinese zodiac animal, stem-branch element, zodiac year and lunar (nominal) age from any birth date.

Enter your birth date to see your Western zodiac sign (Aries, Taurus, Gemini…) along with its element, modality and opposing sign.

Pick a birth month to instantly see the modern and traditional birthstones, the birth flower, the spanning zodiac signs and a colour swatch — handy when choosing jewellery or birthday gifts.

Convert a Gregorian calendar date to its Julian Day Number (JDN) and Modified Julian Day (MJD) — used in astronomy, history, and cross-calendar date math.

Enter any date and compute its ISO 8601 week number, ISO year and weekday — using the Monday-first / first-week-contains-Jan-4 rule.

Enter two clock times (HH:MM[:SS]) and instantly see the difference in hours, minutes and seconds — with overnight-shift handling and decimal-hour output.

Enter years of service and see the statutory paid annual leave entitlement under the HK Employment Ordinance §41AA.

Enter your date of birth to see when your next half-birthday falls, how many days away it is, and your current half-age (e.g. 33.5 years).

Enter a latitude, longitude and date to get the local sunrise, sunset, solar noon and total daylight hours using the NOAA solar position formula.

Enter a target date and get an instant breakdown of days, weeks, months, hours and minutes remaining — or elapsed for past dates.

Enter the number of time zones crossed and direction of travel (eastward or westward) to estimate how many days you typically need to fully adjust to the destination, based on sleep-medicine rules of thumb.

Convert between HH:MM:SS and decimal hours both ways — built for payroll, timesheets and lab notebooks.

Enter a birth year to classify yourself by the Pew Research generation cohorts — Greatest, Silent, Boomer, Gen X, Millennial, Gen Z, Gen Alpha or Gen Beta.

Add or subtract any number of HH:MM:SS durations with automatic carry — handy for totalling video lengths, training sessions or race splits.

Pick any date to see what percentage of the year, quarter, month and week has elapsed and how many days remain — handy for yearly goals, OKR check-ins and progress reports.

Pick a date and see it instantly formatted in ISO 8601, RFC 2822, US (MM/DD/YYYY), EU (DD/MM/YYYY), Japanese (YYYY年MM月DD日), Unix timestamp and a dozen other common formats.

List every Friday the 13th in a given year (or range) and show how many days remain until the next one.

Pick a month, year, weekday and occurrence (including "last") to get the date — handy for scheduling monthly meetings, paydays and rule-based holidays such as US Thanksgiving (4th Thursday of November).

Enter a start and end date and instantly see how many Mondays, Tuesdays, … Sundays fall inside the range, plus weekday vs weekend totals — useful for scheduling, payroll, rent and contract counts.

Enter your birth date and target retirement age; the tool returns the exact years, months, days and total days remaining until retirement, plus the calendar date you will retire — useful for financial and life planning.

Enter latitude, longitude and date; the tool applies the NOAA solar position algorithm to return local sunrise, sunset and solar-noon times, plus the length of the day — essential for photography, outdoor activities, agriculture and solar-energy planning.

Enter a date and your fiscal-year start month; the tool reports the calendar quarter (Q1–Q4), the fiscal quarter and fiscal-year label, the quarter's start/end dates and the percentage of the quarter elapsed — useful for SEC filings, government budgets and SaaS subscription planning.

Enter weekly hours, annual leave days and public holidays; the tool returns net annual working hours after leave and converts a yearly salary into hourly, daily and monthly rates — useful for freelancers, contractors and HR cost planning.

Enter a Gregorian year and the tool returns the dates and UTC times of the spring equinox, summer solstice, autumn equinox and winter solstice using Jean Meeus’ astronomical formulas — useful for gardening, festival planning, photography and the Chinese solar-term calendar.

Enter your birth date; the tool returns your age on Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune using each planet's orbital period — a popular STEM / classroom / museum tool that turns abstract astronomy into a fun, personal number.

Enter the estimated due date or the last menstrual period (LMP); the tool applies the Naegele rule in reverse to estimate the conception date and fertile window (5 days before to day of ovulation), supporting due dates derived from ultrasound CRL — useful for prenatal planning and medical records.

Enter a Gregorian date or a Hijri (Islamic) date; the tool converts between the two using the tabular Umm al-Qura algorithm (also known as the Kuwaiti algorithm) — useful for Islamic festivals (Ramadan, Hajj, Eid), cross-cultural documents and historical records.

Enter a date and a format (DD/MM/YYYY, MM/DD/YYYY, YYYY-MM-DD, etc.); the tool tells you whether it is a palindrome date (reads the same forwards and backwards, e.g. 22/02/2022) and lists the next five upcoming palindrome dates. A fun tool for picking wedding dates, anniversaries or other "perfectly symmetric" days.

Enter a starting year; the tool lists the next 5 leap years (Gregorian rule: divisible by 4 but, if divisible by 100, must also be divisible by 400), each with its distance in years from the start, plus the most recent prior leap year. Useful for project deadlines, birthday-on-Feb-29 planning and calendar trivia.

Enter two dates; the tool simultaneously reports the year fraction t under the four most-used day-count conventions (ACT/ACT, ACT/365 Fixed, ACT/360, 30/360 ISDA). Foundational for bond accrued interest, interest-rate swaps, annuities and insurance actuarial calculations.