Calculate your estimated due date (EDD) from your last menstrual period or conception date.
This tool estimates your expected delivery date based on the first day of your last menstrual period (LMP) or the date of conception, using standard obstetric dating conventions. It's intended as a general estimate — actual delivery dates commonly vary by a couple of weeks in either direction.
This calculator commonly uses Naegele's Rule: Due Date = LMP + 280 days (40 weeks), assuming a standard 28-day cycle with ovulation around day 14. If conception date is known instead, 266 days is added directly.
Enter the first day of your last menstrual period (or your conception date if known), and the calculator estimates your expected due date.
Example: If your last period began on January 1, your estimated due date would be around October 8 of the same year (280 days later).
Only about 5% of babies are actually born on their exact calculated due date — most births occur within a two-week window before or after, so treat this as a general estimate rather than a precise prediction.
Because the exact ovulation and conception date is often unknown, due dates are conventionally calculated from the last menstrual period instead, which adds roughly two extra weeks compared to counting from conception directly.
Yes, this standard calculation assumes a 28-day cycle with ovulation on day 14; individuals with longer, shorter, or irregular cycles may have a less accurate estimate from this method alone.
Often yes — early pregnancy ultrasounds can provide a more precise dating estimate based on fetal measurements, which may adjust the initially calculated due date from LMP.
It's best used as a general planning reference; since actual delivery timing varies naturally, flexibility around the estimated date is generally recommended for practical planning purposes.
Most due date calculators, including this one, rely on Naegele's Rule, a method developed in the 19th century that estimates a due date by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a fairly typical 28-day cycle with ovulation occurring around day 14. If your cycle is longer or shorter than 28 days, your actual ovulation date shifts, which can make the LMP-based estimate slightly less accurate for you personally. Doctors often refine this initial estimate further using an early ultrasound, particularly one done in the first trimester, since ultrasound measurements of the fetus at that stage are considered the most reliable way to confirm gestational age.
It's worth knowing upfront that only a small percentage of babies are actually born on their calculated due date — most arrive within a window of about two weeks before or after it, and that's considered completely normal. Due dates calculated from IVF or a known conception date tend to be more precise than those based purely on the last menstrual period, since they remove the guesswork around exactly when ovulation happened. As your pregnancy progresses, your doctor may adjust your estimated due date based on ultrasound growth measurements, especially if there's a noticeable difference between the LMP-based estimate and what the scan shows. Rather than treating the due date as a fixed deadline, it's more useful to think of it as the midpoint of a normal delivery window.
Once you have an estimated due date, it becomes a useful reference point for tracking key pregnancy milestones — the end of the first trimester around week 13, the anatomy scan typically performed between weeks 18 and 22, viability milestones around week 24, and full term starting at week 37. Many people also use their due date to plan maternity leave, prepare a nursery, or simply get a general sense of how far along they are. Whatever the exact date turns out to be, remember that this calculator provides an estimate based on standard medical formulas, and any decisions about your pregnancy timeline should always be discussed with your obstetrician or midwife, who can factor in your specific cycle history and any ultrasound results.
Once you have your estimate, share it with your doctor at your first prenatal visit so it can be confirmed or adjusted based on a clinical exam and ultrasound. Many hospitals and clinics also use this date to schedule routine screenings at the right gestational week, so having an accurate starting point helps your entire care team stay on the same page throughout your pregnancy.