Calculate your estimated due date, gestational age, and pregnancy milestones using your last menstrual period and cycle length.
Last menstrual period date is required
Enter values above to calculate results.
Estimating an accurate due date is essential for prenatal care planning, timing of screenings, and preparing for delivery. Because cycle lengths vary and recall of last menstrual period (LMP) can be imperfect, clinicians and expectant parents need clear methods for producing the most reliable date possible.
Use cases include scheduling prenatal ultrasounds, planning maternity leave, and monitoring fetal development milestones. Inaccurate dating can lead to mistimed interventions, unnecessary inductions, or missed opportunities for early screening.
If LMP = Jan 1 and cycle length = 30 days → base due date Jan 1 + 280 = Oct 8; adjust +2 days → Oct 10. Gestational age is current date minus Jan 1.
Obstetricians, midwives, and sonographers use due date estimation to schedule critical prenatal tests (NT scan, anatomy scan) and to assess fetal growth. Best practice: confirm LMP-based dating with an early ultrasound (6–12 weeks) which is more accurate.
When discrepancies occur between LMP and ultrasound, clinicians decide which dating method to prioritize; our calculator highlights this and recommends clinical follow-up.
A timeline showing LMP → conception window → trimesters → estimated due date helps expectant parents and clinicians visualize milestones and schedule care appropriately.
Using our Pregnancy Due Date Calculator is simple and requires just two key pieces of information:
This calculator uses Naegele's Rule, the standard method used by healthcare providers worldwide, which adds 280 days (40 weeks) to the first day of your last menstrual period, adjusted for your specific cycle length.
Your Pregnancy Due Date Calculator provides comprehensive pregnancy timeline information:
The most likely date for your baby's arrival, though only about 5% of babies are born exactly on their due date. Full-term delivery can occur anywhere from 37-42 weeks.
How far along you are in your pregnancy, expressed in weeks and days. This helps track fetal development and schedule appropriate prenatal care.
Which trimester you're currently in and when each trimester ends:
The approximate date when conception occurred, typically around ovulation (about 14 days after LMP for a 28-day cycle).
Our calculator uses Naegele's Rule with cycle length adjustment for accurate due date estimation:
Due Date = LMP + 280 days + (Cycle Length - 28 days)
The standard medical formula used globally for due date calculation
Step 1: Add 280 days (40 weeks) to LMP
Step 2: Adjust for cycle length if different from 28 days
Step 3: Calculate gestational age from LMP to current date
For LMP of January 1, 2024, with a 30-day cycle:
Knowing your accurate due date is crucial for optimal pregnancy care and outcomes:
Plan appropriate timing for prenatal visits, screenings, and tests throughout your pregnancy.
Monitor baby's growth and development milestones at the appropriate gestational ages.
Prepare for delivery, plan maternity leave, and make necessary arrangements around your due date.
Identify potential complications like preterm labor or post-term pregnancy for appropriate medical intervention.
Healthcare providers use due dates to guide important decisions about prenatal care, screening schedules, and delivery planning throughout your pregnancy journey.
Follow these guidelines for the most accurate due date estimation:
Pregnancy due date calculations serve essential purposes across various healthcare and personal planning contexts:
Due date calculations are estimates, with only about 5% of babies born on their exact due date. Most babies (about 90%) are born within two weeks of their due date. First pregnancies tend to go slightly longer, while subsequent pregnancies may be shorter.
If you have irregular cycles, LMP-based calculations may be less accurate. Your healthcare provider may rely more heavily on early ultrasound measurements (especially before 12 weeks) or use ovulation tracking data if available.
Early ultrasound between 6-12 weeks provides the most accurate dating, with accuracy within 3-5 days. Dating becomes less accurate as pregnancy progresses due to individual variations in fetal growth patterns.
Healthcare providers typically use ultrasound dating if there's a significant discrepancy (more than 7-10 days) with LMP dating, especially if the ultrasound is performed early in pregnancy. Your provider will explain which date to use.
Due dates are typically established early in pregnancy and rarely change unless there's significant new information. However, your provider may adjust expectations based on baby's growth patterns or other factors discovered during pregnancy.
Many factors influence labor timing including: first vs. subsequent pregnancies, maternal age, stress levels, baby's position, overall health, and genetic factors. Each pregnancy is unique, so past experiences may not predict future ones.
Our Pregnancy Due Date Calculator uses Naegele's Rule, the internationally recognized standard method for estimating due dates in clinical practice.
Developed by German obstetrician Franz Naegele in the early 1800s. This method adds 280 days (40 weeks) to the first day of the last menstrual period, based on the assumption of a 28-day menstrual cycle with ovulation occurring on day 14.
Our calculator adjusts for individual cycle lengths by adding or subtracting the difference from 28 days, providing more personalized estimates for women with shorter or longer cycles.
Multiple studies have validated Naegele's Rule, showing it provides accurate estimates for about 70-80% of pregnancies within a two-week window of the actual delivery date.
This calculator provides estimates for educational purposes only and should not replace professional medical advice. Healthcare providers use additional clinical information, physical examinations, and ultrasound measurements for official pregnancy dating. Always consult your healthcare provider for comprehensive prenatal care.
