Pregnancy Due Date Calculator

How Pregnancy Due Date Calculation Works

The estimated due date (EDD) is calculated from the beginning of the last menstrual period (LMP) using Naegele's Rule — the standard method used by obstetricians worldwide. Pregnancy is considered to last 280 days (40 weeks) from the first day of the LMP, assuming a 28-day cycle.

Naegele's Rule (LMP Method)

The most common due date calculation adds 280 days to the first day of the last menstrual period. For non-28-day cycles, the calculator adjusts by the difference between your cycle length and 28 days. This is the method used in most clinical settings and obstetric software.

• Formula: EDD = LMP + 280 days + (cycle length − 28)

Conception Date Method

If you know your conception or ovulation date, pregnancy is calculated as 266 days (38 weeks) from that date, since conception typically occurs approximately 14 days after the LMP in a 28-day cycle.

IVF Transfer Date Methods

• Day-3 Transfer: EDD = transfer date + 263 days
• Day-5 Transfer (blastocyst): EDD = transfer date + 261 days

Trimesters

• First Trimester: Weeks 1–13 — organogenesis, highest miscarriage risk
• Second Trimester: Weeks 14–26 — foetal growth, typically the most comfortable period
• Third Trimester: Weeks 27–40 — rapid growth, preparation for birth

For monitoring during pregnancy, use our blood pressure tracker to detect preeclampsia risk, and our calorie calculator to estimate nutritional needs per trimester. After birth, our pediatric dose calculator and APGAR score tool support newborn care. For all pregnancy-related tools visit our Medical tools hub.

⚠️ The estimated due date is an approximation. Only about 5% of babies are born on their exact EDD. Always confirm your due date with your obstetrician via ultrasound dating, especially in the first trimester.