Pregnancy Due Date Calculator

A pregnancy due date calculator estimates the expected date of delivery (EDD) based on the first day of the last menstrual period (LMP) or a known conception date. The calculated due date represents the end of a full-term pregnancy of approximately 40 weeks (280 days) from the LMP. It also shows the current week of pregnancy, which trimester the pregnancy is in, and an approximate schedule of important prenatal milestones.

Knowing the due date is essential for prenatal care scheduling, determining appropriate gestational age for screenings (first trimester nuchal translucency scan at 11–14 weeks, anatomy scan at 18–20 weeks), and planning maternity leave and hospital bookings. Only about 5% of babies are born on their exact due date — most arrive within 2 weeks before or after — but the EDD provides the anchor for all obstetric management decisions.

This calculator supports two input methods: the LMP method (standard clinical approach) and the conception date method. When the conception date is known (e.g., from IVF or a precisely tracked ovulation window), it can give a more accurate result for women with irregular cycles. The calculator also adjusts for cycle lengths other than the standard 28-day cycle.

The standard medical formula for calculating the estimated due date is Naegele's Rule, named after German obstetrician Franz Karl Naegele who described it in 1812.

Viability (survival outside the womb with intensive care) begins around 22–24 weeks. Full-term pregnancy is defined as 39–40 weeks. Early term: 37–38 weeks; Post-term: 41+ weeks.

1. Choose a Calculation Method: Select "LMP" (last menstrual period — most common) or "Conception Date" (if you know the exact conception date).
2. Enter the Date: For LMP, enter the first day of your last period. For conception, enter the date conception occurred.
3. Enter Cycle Length: If your cycle is not 28 days, enter your average cycle length. This adjusts the due date for irregular cycles.
4. Read Results: The estimated due date, current gestational age in weeks and days, trimester, and days remaining until the due date are displayed.

Important: This calculator is for informational purposes only. Consult a healthcare provider for official gestational age assessment, which typically uses first-trimester ultrasound for the most accurate dating.

Obstetricians and midwives use the EDD to schedule prenatal screenings at the optimal gestational windows. The first-trimester combined screening (nuchal translucency + blood test) must be performed between 11 weeks 0 days and 13 weeks 6 days — knowing the exact EDD ensures patients are booked at the right time.

HR departments and employees use the EDD to calculate maternity/paternity leave start dates, FMLA eligibility periods, and disability insurance claims. Many jurisdictions define maternity leave relative to the expected or actual delivery date, making accurate due date calculation legally important.

Hospital birth centers use the EDD for scheduling birth suite availability, midwife and anesthesiologist call scheduling, and capacity planning. Insurance companies use it for preauthorization of delivery-related hospital stays.