Pregnancy Calculator
Calculate the expected due date and pregnancy timeline.
Pregnancy Due Date Calculator: Estimate Your Due Date & Weekly Trimester Milestones
You see two pink lines on a home pregnancy test, and an overwhelming rush of excitement and anticipation fills the room. Almost immediately, the first question on every expectant parent's mind is: "When will our baby arrive? When is our due date?"
Calculating your estimated due date (EDD) isn't just about picking a date on the calendar. It helps you schedule prenatal medical appointments, plan maternity and paternity leave, schedule routine ultrasound scans, and prepare your nursery before your baby arrives.
Our free Pregnancy Due Date Calculator calculates your estimated date of delivery using clinical obstetric standards (Naegele's Rule). Calculate your timeline from your Last Menstrual Period (LMP), exact conception date, or IVF embryo transfer date, and explore week-by-week development milestones across all three trimesters.
The Medical Math: How Due Dates Are Calculated (Naegele's Rule)
Clinicians track human pregnancy across an average span of 40 weeks (280 days) from the first day of the mother's Last Menstrual Period (LMP). In 1812, German obstetrician Franz Naegele established the standard formula used in obstetrics today:
Example: If your last period started on May 10, adding a year brings you to May 10 next year. Subtracting 3 months brings you to February 10, and adding 7 days yields an estimated due date of February 17.
Your 40-Week Journey Across the Three Trimesters
First Trimester (Weeks 1 – 12)
Foundation & OrgansThe period of rapid cell division and organogenesis. The neural tube forms, and early embryonic heart activity is typically detected on ultrasound around Week 6. Morning sickness, fatigue, and hormonal shifts peak.
Second Trimester (Weeks 13 – 26)
Growth & MovementOften considered the most comfortable trimester as early nausea subsides. Parents usually feel first fetal flutters (quickening) between Weeks 18 and 22. The detailed mid-pregnancy anatomy scan (Level II ultrasound) takes place around Week 20.
Third Trimester (Weeks 27 – 40+)
Maturation & BirthThe baby puts on insulating body fat, lungs develop surfactant for breathing air, and the baby typically rotates into a head-down (cephalic) birth position. Reaching 37 weeks marks early term, and 39 weeks is considered full term.
The Due Date Reality Check: The 4% Rule
It may surprise you to learn that only about 4% to 5% of babies are born on their exact calculated due date.
Your due date should be viewed as an estimated reference midpoint rather than an immovable deadline. A healthy full-term birth naturally occurs anywhere between 37 weeks and 42 weeks. First-time mothers routinely carry babies past 40 weeks, while twins or multiples often arrive closer to 36 or 37 weeks.
Frequently Asked Questions
Can my doctor adjust my due date later?
Yes. If your early first-trimester dating ultrasound (crown-rump length measurement) differs by more than five to seven days from your period calculation, your OB-GYN or midwife will update your official due date based on the ultrasound scan.
What if my menstrual cycle is longer or shorter than 28 days?
Standard Naegele's math assumes a 28-day cycle with ovulation occurring on Day 14. If you have an irregular or 35-day cycle, our calculator adjusts for your custom cycle length to ensure the ovulation day is accurately factored into your estimated date.
Medical Disclaimer
This calculator provides general informational estimates based on standard statistical formulas. It is not medical advice. Always consult your qualified healthcare provider, obstetrician, or certified nurse-midwife for clinical prenatal care and diagnosis.