Pregnancy Due Date Calculator
The pregnancy due date calculator estimates your expected delivery date from your last menstrual period (LMP). Returns your estimated due date, current pregnancy week, trimester, and a timeline of key milestones. Free, no account needed. Always confirm with your healthcare provider.
How to use Pregnancy Due Date Calculator
- Enter the date of your last menstrual period using the date picker.
- Your estimated due date (EDD) appears instantly based on Naegele's rule.
- See your current pregnancy week and trimester.
- Review the milestone timeline showing key dates throughout your pregnancy.
- Share the result with your healthcare provider for confirmation.
Due date calculator by LMP: how Naegele's rule works
The due date calculator by LMP uses Naegele's rule, the standard obstetric formula for estimating the expected date of delivery (EDD). Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. Equivalently, take the date of your LMP, add one year, subtract three months, and add seven days. This assumes a 28-day menstrual cycle with ovulation on day 14. The formula has been in use since 1812 and remains the starting point for estimating due dates in clinical practice worldwide.
Human pregnancy lasts approximately 280 days from the LMP, or 266 days from conception. The discrepancy exists because the LMP is a known, documentable date while conception typically occurs 14 days later during ovulation and cannot be precisely dated without medical assistance. The when is my baby due estimate from Naegele's rule is an approximation, only about 4 percent of babies are born exactly on their estimated due date. The full-term range is between 37 and 42 weeks of gestation.
Pregnancy week by week calculator: trimesters and milestones
The pregnancy week by week calculator displays your current week of gestation alongside key developmental milestones. The first trimester spans weeks 1 to 13. The second trimester covers weeks 14 to 27. The third trimester runs from week 28 to delivery. Each trimester is associated with distinct developmental phases: the first trimester sees all major organ systems form; the second trimester is characterized by rapid growth and fetal movement; the third trimester involves weight gain and lung maturation in preparation for birth.
The estimated due date calculator also shows the first trimester weeks calculator perspective: important early milestones include the first prenatal appointment (typically around week 8–10), the nuchal translucency screening window (weeks 11–14), anomaly scan (typically week 18–21), and glucose tolerance test (typically week 24–28). Use the how many weeks pregnant am I result to track which screenings and appointments are relevant at your current stage. Always confirm dates and milestones with your obstetrician or midwife.
Frequently asked questions
The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. If your cycle is regularly longer or shorter than 28 days, your healthcare provider may adjust the due date accordingly. Naegele's rule gives an estimated due date, not a precise delivery date. About 80 percent of births occur within two weeks of the calculated due date.
An LMP-based due date is an estimate with inherent uncertainty. Only about 4 percent of babies are born on their exact calculated due date. Around 80 percent of births occur within two weeks of the EDD. The LMP method is least accurate for women with irregular cycles or cycles significantly different from 28 days. An early ultrasound (performed between 8 and 13 weeks) provides a more accurate due date by measuring fetal size and is the preferred method in clinical settings when there is any uncertainty.
The first trimester spans from conception (week 1) through week 13. The second trimester covers weeks 14 through 27. The third trimester runs from week 28 through delivery at approximately week 40. The first trimester is the period of highest miscarriage risk and most critical organ formation. The second trimester is typically when fetal movement is first felt. The third trimester is characterized by rapid fetal weight gain and preparation for birth, including lung maturation and descent into the pelvis.
You should book a first prenatal appointment as early in the first trimester as possible, ideally before week 10. Your healthcare provider will confirm your estimated due date through clinical history and, most accurately, through an early dating ultrasound (typically performed between 8 and 13 weeks). The ultrasound measures fetal crown-rump length to estimate gestational age with greater precision than the LMP method alone. Do not rely solely on a calculator-generated date for medical planning.