Sidereal Time Calculator (GMST / LST)

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.

Enter two people's birth dates; the tool returns the gap in years, months and days, plus the total day count and a percent comparison. Answers the most-Googled "how much older am I than my partner / sibling?" question.

Enter your birth date; the tool returns the days and weeks remaining until your next birthday, the age you will be turning and the weekday it falls on — handles the Feb 29 leap-year case (rolling celebrations to Mar 1 in non-leap years per common convention).

Enter any past date; the tool instantly reports the days, weeks, months and years elapsed since — handy for sobriety milestones, baby month-counts, employee tenure, product launch days, relationship anniversaries and any other "time since the event" tracker.

Enter check-in and check-out dates; the tool returns nights (the unit hotels actually charge) and total inclusive days (counting arrival and departure) — the standard tool for booking comparisons and trip planning anywhere in the world.

Enter the book's total pages, pages already read, how many pages you plan to read per day and the start date; the tool returns the projected finish date and the number of days remaining — useful for reading challenges, Goodreads goals and textbook planning.

Enter the deadline and the number of business days needed; the tool counts backwards, skipping Saturdays and Sundays, to return the latest possible start date — useful for SLA countdowns, project scheduling and signing-deadline reminders.

Enter your birth date and average resting heart rate to see how many beats your heart has logged so far, and to project the lifetime total at your expected lifespan — a sobering perspective shift.

Enter two dates and instantly read the exact day in the middle — useful for half-anniversaries, project mid-point check-ins, the median day of a trip, plus a "you are X% through the span" progress indicator.

Enter a birth date and any target date (past or future); the tool returns exact age (years / months / days) and total days lived on that date — handy for graduation day, retirement, visa age cutoffs and insurance renewals.

Enter the hire date and a snapshot date (defaulting to today); returns tenure in years-months-days, total days of service, the countdown to the next work anniversary and the next service-award milestone (5 / 10 / 15 / 20 / 25 / 30 yr).

Enter your date of birth to see how many days, weeks, hours and minutes you have been alive — and what fraction of an average lifespan that represents.

Enter the first day of your last period and average cycle length to identify the current phase (menses / follicular / ovulation / luteal) and days until the next period.

Enter total episodes, runtime per episode and how many minutes you can watch per day to see how many days the binge will take and the predicted finish date.

Enter two cities' UTC offsets and working hours to find the overlap window in both local times — useful for scheduling cross-timezone meetings.

Enter a year and a month to find the last day of that month (with weekday), the number of days in the month, the count of each weekday in the month and whether the year is a leap year.

Enter a year to instantly check if it is a leap year (Gregorian / Julian), see the rule explanation and the previous & next leap years.

Enter a date of birth and a forecast horizon — get the weekday and age for each upcoming birthday, so you can plan ahead for that next weekend birthday.

Pick a period (today / week / month / quarter / year) to see what percentage has elapsed, how many days remain and a visual progress bar — handy for deadline pacing.

Enter your date of birth to instantly see how many days, hours, minutes and seconds remain until your next birthday, the weekday it falls on, the age you turn and the corresponding zodiac sign.

Enter hours, minutes and seconds to get the percent of the 24-hour day elapsed, seconds since midnight, seconds remaining and the equivalent Swatch Internet Time (.beats).

Climate datasets, demography papers and astronomy commonly use *decimal years* (e.g. 2024.5). Convert calendar date ↔ decimal year both ways, with leap-year handling.

Enter any Gregorian date and get the matching Mayan Long Count (baktun.katun.tun.uinal.kin) plus the Tzolkin (260-day) and Haab' (365-day) calendar-round positions.

Convert any Gregorian date to the Coptic / Alexandrian calendar (basis of the Ethiopian calendar): 12 × 30-day months plus the short "Nasie" intercalary month, counted from the Era of Martyrs (29 August 284 CE).

Convert in both directions between Japan's imperial era years (Reiwa, Heisei, Shōwa, Taishō, Meiji) and the Gregorian calendar — enter a Gregorian year with month/day, or pick an era and year to get the matching Western year.

Taiwan and many Chinese-language official documents use the ROC / Minguo era (1912 = year 1). Convert either direction instantly and see the equivalent Buddhist Era (BE) and Korean Dangi year alongside.

Enter an old year and find the next year whose January 1st falls on the same weekday and whose leap status matches — i.e. the next year your old wall calendar can be reused exactly.

Pick a region (US / Canada / EU / UK / Australia / NZ / Chile etc.) to list the exact spring-forward and fall-back dates of Daylight Saving Time for any year — handy for adjusting clocks on watches, appliances and travel itineraries.

Enter a year — using the Meeus algorithm the tool returns the date of Orthodox (Eastern / Greek / Russian Orthodox) Easter, typically 0, 4 or 5 weeks after Western (Catholic / Protestant) Easter.

Enter a Gregorian year — the tool returns the date of Chinese Lunar New Year (Spring Festival) and the zodiac animal for that year. Covers 1900–2100 via the standard reference table, accurate to ±1 day.

Enter a Gregorian year — the tool returns the dates of all 24 solar terms (Lichun 立春, Yushui 雨水, Jingzhe 驚蟄 … Dahan 大寒). These divisions of the solar year are used in Chinese, Japanese, Korean and Vietnamese traditional calendars to schedule farming, festivals and seasonal practices.

Enter an Earth UTC date and time — the tool returns the Mars Sol Date (MSD) and Coordinated Mars Time (MTC), the same scheme NASA / JPL mission teams use. One sol is ~24 h 39 m 35.244 s.

Enter a date of birth; the tool simultaneously shows the three age systems used in Korea — *se-neun nai* (Korean age: 1 at birth, +1 every Jan 1), *man nai* (international age, now South Korea's legal age since June 2023) and *yeon nai* (year age = current year − birth year). Useful for K-drama context, military service age, school-entry checks and expat paperwork.

Enter a Gregorian year (A.D.) to get the corresponding Thai Buddhist year (B.E. = พุทธศักราช = A.D. + 543), or vice versa; the tool also reports the +544 offset used in Cambodia, Sri Lanka, Myanmar and the Vietnamese religious calendar. Essential when reading Thai newspapers, passports, visa forms, government records and royal proclamations.

Enter today's date (defaults to today); the tool computes how many workdays (Mon–Fri, with optional custom holidays) remain in the current month, quarter and year — useful for employees, students and project managers estimating deliverable timelines.

Enter departure local time, flight duration and the UTC offsets at origin and destination; the tool returns the arrival local time, an across-midnight flag and the real elapsed clock-time — the essential tool for picking up someone at the airport.

Enter any year; the tool applies the Gregorian leap-year rule (divisible by 4, except by 100 unless also by 400) to tell you whether that year is a leap year, find the next leap year, list the next five leap years and the gap between them.

Enter your birth date to find your "golden birthday" — the year your age equals the day of the month you were born (e.g. born on the 22nd → age 22), with its date, weekday and countdown.

Enter your birth date; the tool reduces the year, month and day and adds them using numerology to give your Life Path Number 1–9 (or master numbers 11 / 22 / 33).

Enter your birth date and life expectancy to see how many weeks you have lived, what percentage of your life that represents, and roughly how many weeks remain.

Enter a date and hemisphere to see which season it falls in — showing both the meteorological season (by month) and the astronomical season (by equinoxes and solstices).

Enter a date to find which week of the month it falls in (simple ceil(day/7) and calendar-row methods), which "nth weekday" it is, and how many weeks the month spans.

Convert any date into Roman numerals (e.g. XI · VII · MMXXVI) in your choice of day/month order — ideal for anniversary tattoos and engravings.

From a resignation date and notice period (days/weeks/months), work out your last working day, optionally rolled off weekends.

Enter two date ranges to find how many days they overlap, plus the overlap start and end dates.

Work back from your last frost date and a seed's recommended head-start to get the indoor sowing, hardening-off and transplant dates.

Enter a time to see the traditional Chinese two-hour "shichen" (Zi, Chou, Yin…), its time range and the matching earthly-branch zodiac animal.

From a birth date, work out a baby's age in weeks, months and total days to line up with growth milestones and vaccine schedules.

Enter a year and ISO week number to get the Monday–Sunday date range for that week.

Enter a start and end date and pick a pay frequency (weekly, biweekly, semi-monthly or monthly) to count how many pay periods and paychecks fall in between.

Compute the physical, emotional and intellectual biorhythm cycles as percentages from your birth date and a target date.

From a start date and a fixed interval (every N days / weeks / months), list the next N occurrence dates.

From a start and end date, compute the percentage elapsed today plus days done and days remaining.

From a start date, find the date of the next (or Nth) occurrence of a given weekday and how many days away it is.

Count how many Saturdays, Sundays, weekend days and full Sat–Sun weekends fall between two dates.

Add up multiple flight legs and layovers to get total journey time, total flying time and total layover time.

Enter each day's clock-in, clock-out and break time to total your weekly hours worked and overtime as decimal hours.

Enter a date to find its ISO 8601 week number of the year (weeks start on Monday).

Add a number of working hours to a start time, counting only office hours and skipping evenings and weekends, to get the deadline.