Pregnancy Due Date Calculator
Use this pregnancy due date calculator to estimate your delivery date, track your current gestational age, and map out each trimester. Whether you are calculating by last menstrual period (LMP), conception date, ultrasound date, or IVF transfer, get an accurate medical estimate in seconds.
How Does a Pregnancy Due Date Calculator Work?
A pregnancy due date calculator estimates your delivery date by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). It determines fetal gestational age, tracks development milestones, and adjusts for your unique menstrual cycle length.
Clinical pregnancies are measured from the start of your LMP rather than the exact day you conceive. Because conception and ovulation typically happen two weeks after your period starts, the first two weeks of the 40 weeks gestation count toward your overall pregnancy timeline.
How Doctors Calculate Due Date: Naegele's Rule
Obstetricians rely on Naegele's rule for standard calculations. The formula assumes an average 28-day cycle with ovulation occurring on day 14. If your cycle is longer or shorter, the date shifts accordingly.
Estimated Delivery Date (EDD) = LMP + 7 Days - 3 Months + 1 Year + (Cycle Length - 28 Days)Step-by-Step Example Calculation:
- First day of LMP: May 10, 2026
- Add 7 days: May 17, 2026
- Subtract 3 months: February 17, 2026
- Add 1 year: February 17, 2027
- Cycle adjustment: For a 30-day cycle (+2 days), the final EDD is February 19, 2027.
Alternative Calculation Methods:
- Due date calculator based on conception date: Add 266 days (38 weeks) directly to your known ovulation date.
- Due date calculator by IVF transfer date: For a Day 3 transfer, add 263 days. For a Day 5 blastocyst transfer, add 261 days.
- Due date calculator by ultrasound date: Uses crown-rump length (CRL) during an early scan to establish an authoritative timeline.
Trimester Breakdown & Gestational Milestones
A full-term pregnancy spans between 37 and 42 weeks, divided across three clinical stages:
- First Trimester (Weeks 1 – 12): Begins on the first day of your LMP. The fertilized egg implants, forming the placenta and foundational neural and organ structures.
- Second Trimester (Weeks 13 – 26): Fetal anatomy develops rapidly. Bone density increases, the baby begins moving, and sex can usually be identified on an anatomy ultrasound.
- Third Trimester (Weeks 27 – 40+): Rapid weight gain and lung development. A pregnancy is officially considered early term at 37 weeks and full term between 39 weeks, 0 days and 40 weeks, 6 days.
Frequently Asked Questions
How is my due date calculated?
Your due date is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). If you calculate by conception date or ovulation date, 266 days (38 weeks) are added to account for the post-ovulation timeline.
How many weeks pregnant am I based on due date?
To find your current gestational age, count backwards from your due date. Since a full term is 40 weeks (280 days), subtract the number of remaining days until your due date from 280, then divide by 7.
Can a due date change after an ultrasound?
Yes. If an early first-trimester dating ultrasound differs from your LMP calculation by more than 5 to 7 days, your healthcare provider will update your estimated delivery date based on the ultrasound measurements.
What percentage of babies are born on their due date?
Only around 4% to 5% of babies arrive on their exact calculated due date. Most healthy births occur within the full-term window between 37 and 42 weeks of gestation.
How do doctors calculate due date from last period?
Doctors use Naegele's rule: identify the first day of your LMP, add 7 days, subtract 3 months, and add 1 year. This gives your estimated delivery date based on a standard 280-day gestational cycle.
Pregnancy Due Date Calculator
Conception Window: --- | Countdown: 0 Days to Birth
* Estimated Due Date (EDD) calculations follow standard American College of Obstetricians and Gynecologists (ACOG) and Naegele’s clinical guidelines. Only about 4% to 5% of babies are born on their exact due date; delivery typically occurs between 37 and 42 weeks. Consult your OB-GYN or midwife for ultrasound confirmation and clinical prenatal care.
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