Pregnancy Calculator

Select the dating method your care team uses most often: LMP is the classic starting point (first day of bleeding, not spotting). If you know conception date or an early ultrasound estimate, some workflows prefer those anchors. Enter the date and review the projected due date and week of gestation.

Gestational age in obstetrics is usually counted from LMP, so "week 12" includes roughly two weeks before conception in a typical 28-day cycle—that is why pregnancy is described as lasting about 40 weeks from LMP even though fertilization occurred later.

A common textbook method is Naegele's rule: add one year, subtract three months, and add seven days to the first day of the LMP (with calendar adjustments at month boundaries). Another equivalent framing is LMP + 280 days (40 weeks). Your app may use precise calendar arithmetic rather than the simplified rule, but the intent is the same.

Ultrasound dating in the first trimester can revise the due date when it differs from LMP-based dating by more than a small margin—your provider will document the official estimated due date (EDD).

LMP is a visible, memorable anchor most people know. Conception day is often unknown, and implantation adds further variability. Clinical guidelines therefore standardized on LMP-based gestational age while acknowledging it is an approximation.

Longer or shorter cycles shift ovulation relative to LMP, so LMP-only dating can be off by days or more. Early ultrasound is especially helpful in that situation. Treat any online estimate as a starting point for discussion with your clinician.

Roughly: first trimester through week 12, second through week 27, third from week 28 until delivery. Exact cutoffs can vary slightly by source; your prenatal schedule is guided by your provider regardless of labels.

• Planning time off: Roughly map when third-trimester rest or parental leave might begin around the EDD window.
• Understanding visit schedules: Align with why certain screenings cluster around week 10–13 or 18–22 per standard guidelines.
• Comparing tools:Sanity-check another app's week counter against the same LMP you enter here.