Estimate your due date and how many weeks pregnant you are
This pregnancy due date calculator works out your estimated due date (EDD) the way clinics do, then shows where you are today: weeks and days pregnant, pregnancy week and month, trimester, days left and the dates of the scans ahead. Start from the first day of your last period, a conception date, an IVF embryo transfer, an ultrasound scan, or a due date you already have — it doubles as a pregnancy week calculator and a gestational age calculator.
Everything is calculated in your browser; nothing about your pregnancy is sent anywhere. It is information only, not a diagnosis — talk to your doctor or midwife about your dates.
How to calculate your due date
- Choose what you know: Last period, Conception, IVF transfer, Ultrasound or Due date.
- Pick the date. For the last-period method this is the first day of bleeding, not the last.
- For last period, enter your usual cycle length; for IVF pick a day-3, day-5 or day-6 embryo; for ultrasound type the weeks and days on the report, or the crown–rump length (CRL) in millimetres.
- Read your due date, weeks pregnant today, trimester and days to go.
- Scroll the milestone timeline, the month-by-month table and the week-by-week calendar for exact dates.
Pregnancy Due Date Calculator features
Five dating methods
Last period, conception, IVF transfer (day 3, 5 or 6), ultrasound (reported age or CRL) and a known due date.
Cycle-length adjustment
Enter a 20–45 day cycle and the due date shifts by the difference from 28 days, because ovulation moves with cycle length.
Week and month views
Today’s week of 40 and month of 9, plus a month-by-month table and a 42-week calendar with dates.
Clinical mode
CRL dating (Robinson or Hadlock) and an ACOG redating check — for clinicians and students.
How the due date is calculated
Pregnancy is counted from the first day of the last menstrual period (LMP), about two weeks before conception, so it “lasts” 40 weeks, or 280 days. Naegele’s rule is the calendar shortcut: add one year, subtract three months and add seven days. The calculator counts 280 days exactly, so it can differ by a day from the shortcut.
Naegele’s rule assumes a 28-day cycle; for a 33-day cycle the calculator adds 5 days, for 25 days it subtracts 3. A conception date + 266 days gives the due date. For IVF, a day-5 blastocyst transfer + 261 days, a day-3 transfer + 263 days. For an ultrasound, the scan date minus the measured gestational age gives an equivalent LMP, and a known due date minus 280 days does the same.
Worked example: a last period on 1 January 2024 with a 28-day cycle gives 7 October 2024; with a 35-day cycle, 14 October 2024.
Gestational age from CRL, and when to redate (clinical mode)
Choose Ultrasound and Crown–rump length to convert a first-trimester CRL into gestational age. The default is Robinson and Fleming (1975) in the BMUS form: GA (days) = 8.052 × √(1.037 × CRL mm) + 23.73. The alternative is Hadlock et al. (Radiology, 1992): GA (weeks) = e^(1.684969 + 0.315646c − 0.049306c² + 0.004057c³ − 0.000120456c⁴), c in cm. A 45 mm CRL is 11w 2d by both. CRL is used only up to 84 mm (about 14 weeks).
Add the last-period date and the tool applies ACOG Committee Opinion 700 (2017, reaffirmed 2022): redate to the scan when the two differ by more than 5 days up to 8w 6d, 7 days to 15w 6d, 10 days to 21w 6d, 14 days to 27w 6d and 21 days after, judged by LMP age. For clinicians and students; check your local protocol.
Trimesters and key pregnancy milestones
The first trimester runs to 13 weeks 6 days, the second from 14 weeks to 27 weeks 6 days, and the third from 28 weeks until birth. The month table uses one common convention — weeks 1–4, 5–8, 9–13, 14–17, 18–22, 23–27, 28–31, 32–35 and 36–40 — and other charts differ by a week. Timings vary by clinic, so follow your appointment letters.
| Weeks | What usually happens |
|---|---|
| 4 | Period is missed; most home pregnancy tests turn positive |
| 11–14 | Dating and first-trimester screening scan (nuchal translucency) |
| 18–22 | Mid-pregnancy anatomy (anomaly) scan |
| 24 | Widely used threshold of viability |
| 24–28 | Glucose screening for gestational diabetes |
| 37–38+6 | Early term |
| 39–40+6 | Full term |
| 41–41+6 | Late term |
| 42+ | Post-term |
Why your due date is only an estimate
A due date is the midpoint of a range. Only around 4–5% of babies are born on the day itself; most arrive between 37 and 42 weeks. Ovulation can come early or late, and period dates are often remembered imperfectly. ACOG considers a first-trimester ultrasound the most accurate way to date a pregnancy, and IVF dates are the most precise of all. If your clinic gave you a scan due date, use the Due date or Ultrasound method so the timeline matches theirs.
To learn your cycle length, log periods in the period calculator; if you are trying to conceive, the ovulation calculator shows your fertile days.
Pregnancy Due Date Calculator FAQ
How accurate is a pregnancy due date calculator?
Only as accurate as the date you enter. LMP dating can be out by a week or more; conception, IVF and early-scan dates are more precise. Babies still arrive across a five-week window, so the result is an estimate, not medical advice.
How many weeks pregnant am I?
Count the days from the first day of your last period to today and divide by seven. “14w 2d” means 14 full weeks and 2 days — you are in your 15th week, month 4.
Why am I already two weeks pregnant at conception?
Gestational age is measured from the start of the last period, which is easier to know than ovulation. Conception happens about two weeks later.
How do I calculate gestational age after IVF?
Choose “IVF transfer”, pick the embryo age and enter the transfer date. The calculator adds 266 days minus the embryo’s age — 261 days for a day-5 blastocyst — as fertility clinics do.
My scan gave a different due date. Which one is right?
Usually the scan, if it was early and the difference is larger than the ACOG threshold for that stage. Enter the scan and your last period in the Ultrasound method to see which date the guideline keeps — then confirm with your doctor or midwife.
What if my cycles are irregular?
Enter your average cycle length if it varies a little. If it varies a lot, a dating scan is the best way to set your due date.