Estimate a due date and gestational age from a known conception date, last period, embryo transfer, or ultrasound dating.
Dating information
Select the method matching your records
Calendar estimate
Date estimates
Estimated due date and calendar landmarks
Your pregnancy estimates will appear here
Choose the method that matches the date information you have.
Estimated due dateConvert the selected dating method to an LMP-equivalent date, then add 280 days
Estimated due date
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Gestational age today
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Estimated conception date
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Approximate 10-week landmark: Doppler
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Approximate end of first trimester
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Approximate 10-week landmark: serum screen
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Approximate 12-week landmark: NT ultrasound
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Approximate 16-week landmark: quad screen
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Approximate 16-week landmark: cervical length
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Approximate 20-week landmark: anatomy scan
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Approximate 26-week landmark: glucose screening
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Approximate 28-week landmark: anti-D
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Approximate 32-week landmark: fetal surveillance
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Approximate 36-week landmark: GBS screen
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Approximate 39-week landmark: elective delivery
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A due date and the displayed week landmarks are estimates, not predictions or a personal appointment schedule. Screening and care schedules depend on individual circumstances and local guidance. Use your maternity team’s established dating, especially when early ultrasound or assisted-reproduction records are available.
What is Pregnancy Calculator?
The Pregnancy Calculator gives an estimated due date and calendar landmarks from one of four dating methods: a known conception date, the first day of the last menstrual period, an embryo-transfer date, or an ultrasound date with the gestational age reported at that scan. It also estimates gestational age for today.
A due date is a planning estimate, not a promise about the day labor will begin. ACOG describes first-trimester ultrasound as the most accurate way to establish or confirm gestational age and recommends using assisted-reproduction details when a pregnancy followed that treatment. A maternity professional should establish the date used for clinical care.
How to Use This Calculator
Select the method that matches the information you actually have. Do not choose conception unless that date is known with reasonable confidence.
For last menstrual period, enter the first day of bleeding and the usual cycle length. For transfer dating, enter the transfer date and whether the embryo was three or five days old. For ultrasound dating, copy the scan date and the reported weeks and extra days.
Choose Calculate. The page converts the selected information to an LMP-equivalent starting date, then adds 280 days.
Review the due date, estimated age and week landmarks. Use the landmark dates as orientation only; they are not a personal appointment schedule.
The form rejects missing method-specific dates, future dates and values outside the offered cycle, embryo-age and scan-age ranges. It cannot judge whether a recalled date or scan entry is reliable.
Formula Used
LMP method: EDD = adjusted LMP + 280 days, with adjustment of cycle length − 28 days. Conception: EDD = conception + 266 days. Embryo transfer: EDD = transfer + 266 days − embryo age. Ultrasound: EDD = scan date + 280 days − gestational age at scan.
Variables Explained
Input
Meaning
Important detail
Last menstrual period
First day of the last menstrual bleeding used for dating.
It is not the final day of bleeding.
Cycle length
Usual number of days from one period’s first day to the next.
The simple adjustment assumes timing changes with cycle length.
Conception date
Estimated date of fertilization.
Intercourse date and fertilization date may differ.
Transfer date and embryo age
Assisted-reproduction transfer details.
Choose the age recorded by the treatment clinic.
Ultrasound date and age
Date of scan plus gestational weeks and days stated on its report.
A date alone cannot establish ultrasound dating.
EDD
Estimated due date at 40 weeks’ gestational age.
Clinical dating may confirm or revise a calendar estimate.
Worked Example
Suppose a five-day embryo was transferred on 10 August 2026. Estimated fertilization date = 10 August minus 5 days = 5 August 2026. The LMP-equivalent date is 14 days earlier, 22 July 2026. Adding 280 days gives an estimated due date of 28 April 2027. The direct check is transfer date + 261 days, which gives the same date.
This example uses the embryo’s age at transfer. Treating the transfer day itself as conception would shift the estimate by five days.
Why Use This Calculator?
Keep the method beside the result. A date based on a remembered period has different evidence from a date assigned using an early scan or assisted-reproduction records. ACOG recommends determining and documenting an EDD as soon as the relevant information is available, with later changes reserved for limited circumstances.
The week dates shown beneath the result are arithmetic landmarks counted from the estimated start. Screening, scans, preventive treatment and fetal surveillance depend on medical history, local guidance and clinical findings. The presence of a date on this page does not mean a test or treatment is needed on that day.
If dates conflict, periods are irregular, the pregnancy followed fertility treatment, or there are concerns about pain, bleeding or reduced movement, contact an appropriate healthcare professional. Seek urgent care for severe or emergency symptoms. Do not delay care while trying different entries in a calculator.
Common Mistakes
Entering the last day of a period rather than its first day.
Assuming intercourse identifies the exact conception date.
Omitting embryo age when using an embryo-transfer date.
Entering an ultrasound date without the gestational age printed on that scan’s report.
Treating every generated week landmark as a booked or recommended appointment.
Expecting the due date to predict the exact day of birth.
Changing an established clinical EDD whenever a later estimate differs.
Frequently Asked Questions
Is the estimated due date the expected day of birth?
It is a reference date for a 40-week pregnancy, not a prediction that labor will occur that day. ACOG notes that only about one in twenty women give birth on the due date.
Why does pregnancy dating begin before conception?
Gestational age is conventionally counted from the first day of the last menstrual period, about two weeks before conception in a textbook 28-day cycle.
Can I use the date when intercourse occurred as conception?
That may be inaccurate because sperm can remain capable of fertilization for several days and ovulation timing can vary. Use a clinician’s established dating when available.
Why does embryo age matter for an IVF transfer?
A three-day and five-day embryo have already developed for different lengths of time before transfer. ACOG recommends using both embryo age and transfer date for assisted-reproduction dating.
What information is needed for the ultrasound method?
Enter the scan date and the gestational weeks and days reported for that scan. The scan date alone provides no measure of how far the pregnancy had progressed.
Are the listed screening dates medical recommendations?
No. They are approximate week markers from the estimated start. A maternity team should decide which tests or visits apply and when they should occur.
When should the estimate be checked by a professional?
Clinical review is appropriate for every pregnancy, especially with uncertain dates, irregular cycles, fertility treatment or conflicting scan findings. Urgent symptoms need prompt care rather than another calculation.