Estimate your pregnancy due date and key trimester milestones.
Estimating a pregnancy due date is one of the very first calculations performed at the start of prenatal care, providing both expectant parents and healthcare providers a framework for timing key prenatal appointments, screenings, and milestones throughout the pregnancy. The CalcEqual Due Date Calculator estimates the expected delivery date using either the first day of your last menstrual period (LMP) or a known conception date, then maps out the boundaries of each trimester based on that estimate.
Healthcare providers use a due date estimate to schedule the timing of important screenings — including first-trimester genetic screening, the anatomy ultrasound typically performed around 18-22 weeks, and glucose tolerance testing for gestational diabetes — all of which are scheduled relative to gestational age rather than calendar date alone. Expectant parents commonly use the estimate for practical planning purposes: scheduling parental leave, preparing a nursery, and setting general expectations with family and employers.
It's essential to understand that a due date is a statistical estimate, not a prediction with any precision — the convention of dating pregnancy from the LMP (rather than the actual, often unknown, conception date) reflects historical practicality, since the LMP date is something most people can identify with reasonable confidence, while the exact conception date often is not precisely known.
Modern obstetric practice increasingly relies on early ultrasound dating to refine or confirm the LMP-based estimate, particularly when a person's menstrual cycle is irregular or significantly different from the standard 28-day cycle this calculation conventionally assumes, since ultrasound measurements of fetal size in early pregnancy can provide a more individually accurate gestational age estimate.
Many fertility tracking apps and at-home ovulation prediction kits allow for more precise conception date estimation than traditional LMP-based dating, which can be particularly useful for those with irregular cycles or who conceived through assisted reproductive technology, where the exact conception or transfer date is already precisely known.
Naegele's Rule is named after German obstetrician Franz Karl Naegele, who formalized the 280-day LMP-based due date estimation method in the 19th century, building on earlier observational traditions in obstetrics. Despite its age, the rule remains the standard baseline calculation used in modern prenatal care worldwide, though it is now typically refined using ultrasound dating rather than relied upon in isolation.
The American College of Obstetricians and Gynecologists (ACOG) provides detailed clinical guidelines on gestational age dating methods, generally recommending that early first-trimester ultrasound measurements take precedence over LMP-based dating alone when there is a significant discrepancy between the two, since ultrasound measurements of fetal crown-rump length in early pregnancy are considered the most accurate dating method available.
Tracking fetal movement and attending all scheduled prenatal visits remain important regardless of the exact due date estimate, since these check-ins monitor pregnancy health markers independent of precise date calculations.
Pregnancy trimester boundaries by gestational week:
| Trimester | Weeks | Approx. Days from LMP |
|---|---|---|
| First | 1–13 | 0–90 |
| Second | 14–27 | 91–189 |
| Third | 28–40 | 190–280 |