Pregnancy Due Date Calculator
Enter the first day of your last menstrual period (LMP) and the calculator instantly returns your estimated due date (EDD), current gestational age in weeks and days, trimester, and how many days remain. It also lists the estimated conception date, the start of the second and third trimesters and the 37-week "full-term" marker — useful for planning antenatal visits and maternity leave. Everything runs in your browser; the link includes your inputs so you can share it with a partner or clinician.
Please enter a valid number
Estimated due date (EDD)
—
Current gestational age
—
Pregnancy milestones
Naegele's rule: EDD = LMP + 280 days (40 completed gestational weeks). Only about 5% of babies arrive exactly on the EDD; spontaneous labour normally happens within two weeks either side. Early ultrasound (CRL measurement) is more accurate than LMP — defer to your doctor or midwife's latest assessment.
Formula
EDD = LMP + 280 days | gestational age = (today − LMP), grouped in 7-day weeks | estimated conception = LMP + 14 days (28-day-cycle assumption)
- · Naegele's rule assumes a 28-day cycle with ovulation on day 14. For longer cycles (e.g. 30–35 days), actual ovulation is later and the LMP-based EDD typically runs a few days early — early-pregnancy ultrasound (CRL measurement) is more accurate.
- · Trimester boundaries follow the clinical convention used by ACOG and the NHS: T1 covers 0w0d–13w6d, T2 covers 14w0d–27w6d, and T3 starts at 28w0d. The same cut-offs are used here.
- · "Term" begins at 37w0d; "full term" is 39w0d–40w6d; "post-term" is 42w0d onwards and usually triggers an offer of induction.
- · In Hong Kong, public antenatal visits at HA clinics are typically spaced 4-weekly, then 2-weekly, then weekly. Statutory paid maternity leave has been 14 weeks since December 2020 (Employment (Amendment) Ordinance 2020).
- · Only about 4–5% of babies arrive on the exact EDD; roughly 80% are born within two weeks either side. The EDD is a planning reference, not a guarantee.
- · Sources: ACOG Committee Opinion 700 (2017, reaffirmed 2023), NHS "Pregnancy week by week", and the Hong Kong Labour Department's Concise Guide to the Employment Ordinance.
Frequently asked
Which date should I enter for LMP?
Enter the first day of bleeding from your last period — not the day it ended, and not the day you think you conceived. Obstetric dating worldwide is anchored to LMP because most people remember when their period started, even though conception actually happens about 14 days later. If your cycles are not 28 days, your doctor will usually re-date the pregnancy using an early ultrasound (CRL measurement between 8–13 weeks).
My cycles are 30 / 35 days — will the EDD be too early?
Yes — Naegele's rule assumes a 28-day cycle with ovulation on day 14. For an N-day cycle, ovulation is (N − 14) days later, so the LMP-based EDD typically runs (N − 14) days early: add 2 days for a 30-day cycle, 7 days for a 35-day cycle. The single most accurate adjustment, though, is an early ultrasound CRL measurement at 8–13 weeks — your clinician will redate the pregnancy if the discrepancy is more than a few days.
When does a pregnancy count as "term", and what happens at 42 weeks?
Since 2013 ACOG splits "term" into early term (37w0d–38w6d), full term (39w0d–40w6d, the lowest-risk natural delivery window), late term (41w0d–41w6d) and post-term (42w0d onwards). Stillbirth risk rises after 41–42 weeks, so induction is typically offered between 41 and 42 weeks in Hong Kong and internationally — the exact timing is an individual decision with your obstetrician.
How is maternity leave calculated in Hong Kong?
Since 11 December 2020, Hong Kong's statutory maternity leave is 14 weeks (up from 10), all paid at 80% of average wages (the government reimburses employers for weeks 11–14, capped at HK$80,000 per employee). Leave usually starts 2–4 weeks before the EDD and the employee must give the employer prior notice of the expected confinement. Refer to the Labour Department's latest guidance for the exact entitlements that apply to your contract.
Related tools
Age Calculator
From your date of birth, get exact age, Chinese nominal age (虛歲), days lived and days to next birthday.
Date Difference Calculator
Enter any two dates to get the calendar gap, working days, weekend days, plus year/month/day breakdown and total weeks/months.
Time Zone Converter
Pick your local and target cities to convert a given clock time across time zones.
Date Add / Subtract Calculator
Add or subtract years, months, weeks and days from a start date to get the resulting date and weekday.
Business Days Calculator
Count the working days between two dates (excluding weekends) — or add N business days to a start date to find the deadline.
Time Card Calculator (clock-in / clock-out / break)
Enter clock-in/clock-out times and break minutes to get total hours worked and gross pay — overnight (graveyard) shifts handled automatically.
Day of Year & Week Number Calculator
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.
Day of the Week Calculator (Any Date)
Enter any Gregorian date (past or future) to instantly find the day of the week — useful for birthdays, anniversaries and historical events.
Unix Timestamp ↔ Date Converter
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.
Easter Date Calculator
Pick a year and the Computus algorithm returns Easter Sunday plus Ash Wednesday, Palm Sunday and Good Friday.
Moon Phase Calculator
Enter any date to compute the lunar phase (new, first quarter, full, last quarter …), moon age in days and illuminated fraction.
Chinese Zodiac & Lunar Age Calculator
Find your Chinese zodiac animal, stem-branch element, zodiac year and lunar (nominal) age from any birth date.
Western Zodiac Sign Calculator
Enter your birth date to see your Western zodiac sign (Aries, Taurus, Gemini…) along with its element, modality and opposing sign.
Birthstone Calculator
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.
Julian Day Number Calculator
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.
ISO 8601 Week Number Calculator
Enter any date and compute its ISO 8601 week number, ISO year and weekday — using the Monday-first / first-week-contains-Jan-4 rule.
Time Between Two Times Calculator
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.
Hong Kong Statutory Annual Leave Calculator
Enter years of service and see the statutory paid annual leave entitlement under the HK Employment Ordinance §41AA.
Half-Birthday Calculator
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).
Daylight Hours (Sunrise / Sunset) Calculator
Enter a latitude, longitude and date to get the local sunrise, sunset, solar noon and total daylight hours using the NOAA solar position formula.