Pregnancy Due Date & Fertile Window Calculator
Calculate your estimated due date, gestational age week-by-week, trimester milestones, and fertile ovulation window with clinical accuracy.
Crucial Pregnancy Milestones & Scans
| Milestone Event | Clinical Window | Estimated Date | Significance |
|---|
⚕ Medical Advisory Notice
Only about 4% to 5% of babies are born on their exact estimated due date. A normal full-term pregnancy comfortably delivers anywhere between 37 weeks, 0 days and 41 weeks, 6 days. Consult your obstetrician or midwife for early dating ultrasound confirmation.
About this tool
How to use it
- Select your calculation method: First Day of Last Menstrual Period (LMP), Conception Date, IVF Transfer, or Fertile Ovulation Window.
- Enter the relevant date in the date picker.
- If calculating by LMP, adjust your average menstrual cycle length (default: 28 days).
- Read your Estimated Due Date (EDD), current gestational week, fruit/vegetable size comparison, and scan milestone calendar.
Why it matters
Human pregnancy length is clinically standardized to 280 days (40 weeks) from the first day of the last menstrual period, assuming a 28-day cycle where ovulation occurs on day 14. Adjusting for longer or shorter cycles prevents inaccurate gestational age estimates.
When to use it
Use this calculator immediately after a positive home pregnancy test, when scheduling early prenatal scans, tracking weekly fetal development, or planning conception intercourse windows.
Good to know
Franz Naegele formulated Naegele's rule in 1812: add 1 year, subtract 3 months, and add 7 days to the first day of the LMP. An ultrasound crown-rump length (CRL) scan between 8 and 12 weeks provides the most accurate clinical confirmation.
Common questions
How accurate is an estimated due date (EDD)?
Only 4% to 5% of babies arrive on their exact calculated due date. However, roughly 85% to 90% of healthy births occur within a 2-week window flanking the due date (between 38 and 41 weeks).
How does cycle length affect the due date?
Ovulation consistently occurs approximately 14 days before the next menstrual period. If your cycle is 32 days long, ovulation occurred on day 18 rather than day 14, shifting your due date 4 days later.
How is an IVF due date calculated?
For a 5-day blastocyst transfer, the due date is calculated by adding 261 days to the transfer date. For a 3-day embryo transfer, add 263 days.
When are the three trimesters?
The First Trimester spans from week 1 through week 12. The Second Trimester spans from week 13 through week 26. The Third Trimester spans from week 27 until delivery (around week 40).