Pregnancy Due Date
Calculator
Enter your last menstrual period or conception date. See your due date, current week, trimester milestones, and key screening appointments — all in one place.
Pregnancy Due Date Calculator: Find Your Baby’s Estimated Arrival Date
Enter your last menstrual period or conception date to calculate your estimated due date, current week of pregnancy, and key milestone dates across all three trimesters.
How Is a Pregnancy Due Date Calculated?
A pregnancy due date — formally called the estimated date of confinement (EDC) or estimated date of delivery (EDD) — is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This standard method, known as Naegele’s Rule, has been used in obstetrics for nearly two centuries and remains the basis for due date calculation worldwide.
The 40-week count assumes a standard 28-day menstrual cycle with ovulation occurring on day 14. If your cycle is shorter or longer than 28 days, your actual due date may differ by several days, and your doctor may adjust your EDD based on early ultrasound measurements.
Naegele’s Rule in plain terms:
Take the first day of your last period → add 1 year → subtract 3 months → add 7 days.
Example: LMP = August 10, 2025 → Due date = May 17, 2026
Three Ways to Calculate Your Due Date
1. Last Menstrual Period (LMP) Method
The most common starting point. Enter the first day of your last period. Works best if your cycles are regular and close to 28 days.
2. Conception Date Method
If you know your approximate conception date — for example, from tracking ovulation or using fertility treatments — enter that date and add 266 days (38 weeks from conception, which equals 40 weeks from LMP).
3. IVF Transfer Date Method
For IVF pregnancies, due dates are calculated from the embryo transfer date:
- Day 3 embryo transfer: Add 263 days
- Day 5 embryo transfer (blastocyst): Add 261 days
How Accurate Is an Estimated Due Date?
Your EDD is an estimate, not a guaranteed delivery date. Research shows that only about 4–5% of babies are born on their exact due date. The majority of full-term babies arrive within a two-week window on either side of the EDD.
- Babies born between 37 and 42 weeks are considered full term
- Fewer than 1 in 10 pregnancies end on the calculated due date
- First-time mothers tend to deliver slightly later than their EDD on average
- Early ultrasound (before 14 weeks) is the most accurate method for confirming gestational age
Your healthcare provider may revise your due date after your first ultrasound if the measurements suggest a different gestational age than the LMP calculation.
The Three Trimesters: What Happens When
Pregnancy is divided into three trimesters, each approximately 13 weeks long. Understanding where you are helps you know what to expect at each prenatal visit and what developmental milestones your baby is reaching.
First Trimester (Weeks 1–12)
The most critical period of fetal development. Major organs form during these weeks. Morning sickness is most common in weeks 6–10. Most miscarriages, if they occur, happen in the first trimester. The first prenatal appointment typically happens around week 8–10.
Key milestones:
- Week 4: Implantation complete, pregnancy test turns positive
- Week 6: Heartbeat detectable by transvaginal ultrasound
- Week 8: All major organs beginning to form
- Week 10: Embryo is now called a fetus
- Week 12: Risk of miscarriage drops significantly; nuchal translucency screening
Second Trimester (Weeks 13–26)
Most people find the second trimester the most comfortable. Morning sickness typically eases. You will begin to feel fetal movement (called quickening) between weeks 16 and 25. The anatomy scan ultrasound — which checks for structural abnormalities and can reveal the sex of the baby — occurs around week 18–20.
Key milestones:
- Week 13: Second trimester begins; miscarriage risk very low
- Week 16–18: Possible to feel first movements
- Week 18–20: Anatomy scan ultrasound
- Week 20: Halfway point of pregnancy
- Week 24: Viability threshold — baby has a chance of survival if born prematurely
- Week 26: Baby’s eyes open for the first time
Third Trimester (Weeks 27–40)
The final stretch. The baby gains most of its weight during these weeks, growing from about 2 pounds at week 27 to an average of 7–8 pounds at term. The baby moves into a head-down position (ideally) between weeks 32 and 36. Group B Strep testing occurs around week 36. Weekly prenatal appointments begin around week 36.
Key milestones:
- Week 28: Third trimester begins; Rh factor injection if needed
- Week 32: Baby is practicing breathing movements
- Week 34: Most major organ systems mature
- Week 36: Group B Strep test; weekly appointments begin
- Week 37: Early full term — safe to deliver
- Week 39–40: Full term; optimal window for delivery
- Week 41+: Post-term; increased monitoring begins
- Week 42: Medical induction typically recommended
Key Prenatal Appointments and Screening Timeline
| Week | Appointment / Screening |
|---|---|
| 8–10 | First prenatal visit, dating ultrasound |
| 10–13 | First trimester screening, NIPT (non-invasive prenatal testing) |
| 11–14 | Nuchal translucency ultrasound |
| 15–20 | Quad screen / AFP blood test |
| 18–20 | Anatomy scan (20-week ultrasound) |
| 24–28 | Glucose challenge test (gestational diabetes) |
| 28 | Rh factor injection (if Rh-negative) |
| 32–34 | Growth ultrasound (if indicated) |
| 35–37 | Group B Strep swab test |
| 36+ | Weekly prenatal appointments |
| 40+ | Non-stress test, biophysical profile (if post-term) |
Gestational Age vs. Fetal Age: What’s the Difference?
Gestational age counts from the first day of your last menstrual period — even though conception hasn’t happened yet. This is the number your doctor uses and the number this calculator shows.
Fetal age (also called embryonic age or conception age) counts from the moment of fertilization — approximately 2 weeks after LMP in a standard 28-day cycle. Fetal age is always about 2 weeks less than gestational age.
When your doctor says you are “10 weeks pregnant,” they mean 10 weeks of gestational age — the baby has only been developing for approximately 8 weeks since conception.
Signs That Labor May Be Starting
As you approach your due date, watch for these signs that labor may be beginning:
- Lightening (baby dropping): The baby descends into the pelvis, making breathing easier but adding pelvic pressure. Can happen 2–4 weeks before labor in first-time mothers, or just hours before in subsequent pregnancies.
- Bloody show: Pink or brown-tinged mucus discharge as the cervix begins to dilate. Can precede labor by days or hours.
- Braxton Hicks contractions: Practice contractions that are irregular and don’t increase in frequency or intensity. Different from true labor contractions.
- Water breaking: Rupture of the amniotic sac, felt as a gush or slow leak of fluid. Call your provider immediately.
- Regular contractions: True labor contractions come at regular intervals, grow closer together, and increase in intensity. The classic guideline is the 5-1-1 rule: contractions 5 minutes apart, lasting 1 minute each, for at least 1 hour.
Frequently Asked Questions
The standard method is Naegele’s Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This calculator does that math instantly and also shows your trimester milestones, key screening dates, and current week of pregnancy.
Use your conception date if you know it (add 266 days), or the date of a positive pregnancy test as a rough guide. Your doctor will use an early ultrasound — the most accurate method — to confirm gestational age and set your official due date.
Yes. If your first ultrasound shows measurements that differ significantly from the LMP-based calculation, your provider may revise your EDD. A difference of more than 7–10 days typically leads to a new official due date based on ultrasound measurements.
What does “full term” mean?
The American College of Obstetricians and Gynecologists (ACOG) defines pregnancy terms as:
Early term: 37 weeks 0 days to 38 weeks 6 days
Full term: 39 weeks 0 days to 40 weeks 6 days
Late term: 41 weeks 0 days to 41 weeks 6 days
Post-term: 42 weeks 0 days and beyond
An ultrasound performed before 14 weeks of pregnancy is the most accurate method for determining gestational age and due date. The earlier the ultrasound, the more accurate — a first-trimester ultrasound is accurate to within 5–7 days.
The first trimester runs from week 1 through the end of week 12. The second trimester runs from week 13 through the end of week 26. The third trimester runs from week 27 through delivery, with week 40 as the standard due date.
Yes. About 50% of pregnancies extend past 40 weeks. Most providers allow pregnancy to continue until 41–42 weeks with increased monitoring. Medical induction is typically recommended by 42 weeks due to rising risks associated with post-term pregnancy.
Pregnancy math works the same regardless of leap years — you are always adding 280 days. If your due date falls on February 29, your provider will use February 28 or March 1 in non-leap years for scheduling purposes.
No — twins share a due date since they share a conception. However, twin pregnancies are typically delivered earlier than singleton pregnancies. The standard target for uncomplicated di/di twins is 38 weeks; for mo/di twins, 36–37 weeks.
IVF due dates are calculated from the embryo transfer date rather than LMP. For a day-5 blastocyst transfer, add 261 days. Your fertility clinic will provide your official EDD based on the transfer protocol used.
Both terms mean the same thing. EDC stands for Estimated Date of Confinement (an older term); EDD stands for Estimated Date of Delivery. Both refer to your calculated due date at 40 weeks of gestation.
Not necessarily for first-time mothers. Most providers recommend waiting until contractions follow the 5-1-1 pattern: 5 minutes apart, lasting 1 minute, for 1 hour. Always call your provider if your water breaks, you experience heavy bleeding, or you have any concerns regardless of contraction pattern.
Related Calculators You May Find Useful
- Age Calculator — Find out exactly how old you will be when your baby arrives
- Date Difference Calculator — Count the exact days remaining until your due date
- BMI Calculator — Track pregnancy weight gain against pre-pregnancy BMI
This calculator is for informational purposes only and does not constitute medical advice. Always consult your obstetrician, midwife, or healthcare provider for your official estimated due date and prenatal care plan.