Estimate the due date of a pregnancy based on the last menstrual period (LMP), an ultrasound, the conception date, or an IVF transfer date. The calculator also shows your current gestational age, trimester, and a full week-by-week pregnancy timeline.
A due date calculator estimates the day a baby is expected to be born. Pregnancy is a journey of roughly 40 weeks, and from the moment a pregnancy is confirmed, one of the very first questions every expectant parent asks is "when is my baby due?" This calculator answers that question in seconds. Enter a single known reference point - the first day of your last menstrual period, the date and measurements from an ultrasound, your conception date, or your IVF embryo transfer date - and the calculator instantly returns your estimated due date (EDD) along with your current gestational age, your trimester, and a complete week-by-week timeline of your pregnancy.
The estimated due date is a cornerstone of prenatal care. It tells your healthcare provider when to schedule screenings and tests, helps you plan maternity leave and prepare your home, and gives you a meaningful countdown to one of life's biggest milestones. While only a small percentage of babies actually arrive on their exact due date, the EDD provides an essential framework around which the entire pregnancy is organized.
Pregnancy is measured in gestational weeks, which are counted from the first day of the last menstrual period (LMP) rather than from the actual date of conception. This convention may seem strange - conception has not occurred during the first two weeks - but it is the universal standard in obstetrics because the LMP is a date most women can identify, whereas the precise moment of conception is rarely known. Under this system, a full-term pregnancy lasts 40 weeks (280 days) measured from the LMP.
The classic method for estimating a due date is Naegele's Rule, named after the German obstetrician Franz Karl Naegele. The rule is simple: take the first day of the last menstrual period, add one year, subtract three months, and add seven days. The result is the estimated due date - which works out to be the same as adding 280 days to the LMP. Our calculator uses this 280-day standard and then adjusts for cycle length, ultrasound measurements, or IVF timing depending on which method you choose.
The LMP method is the most common way to estimate a due date and is the approach most healthcare providers use at the first prenatal visit. You enter the first day of your most recent period and your average cycle length. For a textbook 28-day cycle, the due date is simply the LMP plus 280 days. Because ovulation occurs roughly 14 days before the next period, the calculator adjusts for cycle lengths that differ from 28 days: a longer cycle pushes ovulation - and therefore the due date - later, while a shorter cycle moves it earlier. For example, a woman with a 35-day cycle ovulates around day 21 rather than day 14, so her due date shifts about a week later than a standard calculation would suggest. This calculator supports cycle lengths from 22 to 44 days.
An ultrasound (sonogram) is one of the most accurate ways to date a pregnancy, especially when performed during the first trimester. The sonographer measures the embryo or fetus - most often the crown-rump length (CRL) early on - and reports a gestational age in weeks and days. You enter the date the ultrasound was performed and the gestational age it showed, and the calculator works backward to find the equivalent LMP and forward to establish the due date. First-trimester ultrasound dating is accurate to within about five to seven days, which is why providers often revise an LMP-based due date if an early scan disagrees with it by more than a week.
If you know the date you conceived - perhaps because you tracked ovulation with predictor kits, basal body temperature charting, or fertility awareness - you can calculate your due date directly from it. Because conception corresponds to a fetal age of zero and gestational age of about two weeks, the calculator adds 266 days (38 weeks) to the conception date to find the due date. It also estimates the LMP as 14 days before conception so the gestational-age timeline lines up with clinical conventions. This method works best for women with regular cycles and a confident sense of when they ovulated.
For pregnancies achieved through in vitro fertilization, the due date can be calculated with exceptional precision because every step is documented. You enter the embryo transfer date and select the age of the embryo at transfer - day 3, day 5, or day 6. The calculator converts this to an equivalent conception (fertilization) date by subtracting the embryo's age from the transfer date, then adds 266 days to find the due date. Because the exact timing of fertilization and transfer is known, IVF due dates are among the most reliable of all the methods.
Gestational age describes how far along a pregnancy is, expressed in completed weeks and days since the first day of the last menstrual period. When a provider says you are "ten weeks pregnant," they mean ten weeks have elapsed since your LMP - even though fertilization happened roughly two weeks after that date. As a result, gestational age is about two weeks greater than the embryo's true age (sometimes called fetal age or fertilization age). This is why, at the moment of conception, you are already considered approximately two weeks pregnant in gestational terms.
Gestational age matters because virtually every prenatal guideline is built around it. Screening windows, the timing of the anatomy scan, glucose testing for gestational diabetes, and the definition of "full term" are all expressed in gestational weeks. Knowing your precise gestational age lets you and your provider schedule each test at the right moment and interpret the results correctly.
The first trimester is a period of extraordinary development. After fertilization in week two and implantation in week three, the embryo begins producing human chorionic gonadotropin (hCG) - the hormone home pregnancy tests detect, usually around week four. The heartbeat becomes visible on ultrasound near week six, and during weeks six through ten all the major organ systems take shape. By the end of week twelve the fetus is fully formed in miniature. Common symptoms include nausea, fatigue, tender breasts, and heightened sensitivity to smell, all driven by surging pregnancy hormones.
Often called the "honeymoon" phase, the second trimester usually brings relief from early nausea and a return of energy. The pregnancy begins to show, and around week eighteen many parents feel the baby's first movements and can learn the baby's sex at the anatomy scan. Week twenty marks the halfway point. By week twenty-three, a baby has a chance of survival outside the womb with intensive medical care, a threshold known as viability that improves with every passing week.
The final trimester is defined by rapid growth and the baby's preparation for life outside the womb. The lungs, brain, and immune system mature, and the baby gains weight quickly. By week twenty-eight the baby can open its eyes and practice breathing. Week thirty-seven marks the start of "early term," weeks thirty-nine and forty are "full term," and the due date falls at week forty. Prenatal visits become more frequent - typically every two weeks until week thirty-six, then weekly until delivery.
The week-by-week timeline produced by this calculator highlights the milestones that matter most:
It is important to view the estimated due date as a midpoint rather than a deadline. Only about 4 to 5 percent of babies are born on their exact due date. Roughly 70 percent arrive within ten days of it, and the overwhelming majority are born within the two weeks before or after. A delivery between 37 and 42 weeks is considered normal. The most accurate dating comes from a first-trimester ultrasound, which can pinpoint gestational age within five to seven days; LMP-based dating is reliable for women with regular cycles, and IVF dating is highly precise because fertilization timing is known exactly.
Several factors can make a due date less certain, including irregular menstrual cycles, an unknown or uncertain LMP, late ovulation, and bleeding in early pregnancy that is mistaken for a period. When the LMP-based date and an early ultrasound disagree by more than about a week, providers generally adopt the ultrasound date as the more reliable estimate.
Once you know your due date, you can build a practical plan around it. Early in pregnancy, focus on starting prenatal vitamins with folic acid, scheduling your first prenatal appointment, and making healthy lifestyle choices. The second trimester is an ideal time to plan maternity or paternity leave, begin preparing the nursery, and consider childbirth education classes. As the third trimester progresses, pack a hospital bag, finalize your birth plan, install the car seat, and learn the signs of labor. Using the due date as an anchor helps ensure nothing important is left until the last minute.
As your due date approaches, it helps to recognize the signs of real labor. True labor contractions grow stronger, longer, and closer together over time, often following the "5-1-1" pattern: contractions five minutes apart, each lasting about one minute, continuing for at least one hour. Other signs include the loss of the mucus plug, a trickle or gush of fluid when the membranes rupture (your "water breaking"), and increasing pressure in the pelvis as the baby settles lower. Contact your healthcare provider promptly if your water breaks, if contractions follow the 5-1-1 pattern, if you notice significant bleeding or a decrease in the baby's movements, or if you develop a severe headache, vision changes, or sudden swelling, which can be signs of a serious complication.
The calculator uses the same standard formulas that healthcare providers rely on, so its estimated due date matches the clinical calculation for the information you enter. However, every due date is an estimate. Only about 4–5% of babies are born on their exact due date, and the majority arrive within two weeks on either side. A first-trimester ultrasound is the most accurate way to confirm or adjust the date.
If you are unsure of your LMP, the most reliable alternative is an early ultrasound, which dates the pregnancy from the baby's measurements. You can also use the conception date method if you tracked ovulation, or the IVF method if your pregnancy resulted from in vitro fertilization. Choose whichever method matches the information you have.
Yes. The standard 280-day calculation assumes a 28-day cycle with ovulation on day 14. If your cycles are consistently longer or shorter, ovulation - and therefore conception - happens later or earlier, shifting the due date accordingly. This calculator adjusts automatically for cycle lengths between 22 and 44 days.
Gestational age is counted from the first day of the last menstrual period and is the standard used in prenatal care. Fetal age (or fertilization age) is counted from conception, which occurs about two weeks after the LMP. Fetal age is therefore roughly two weeks less than gestational age. When a calculator or doctor says "8 weeks pregnant," they mean 8 weeks of gestational age.
For IVF pregnancies, the calculator works from the embryo transfer date and the embryo's age at transfer. For a day-5 blastocyst transfer, fertilization is dated five days before the transfer; for a day-3 transfer, three days before; and for a day-6 transfer, six days before. The due date is then 266 days after that fertilization date. Because IVF timing is documented precisely, these due dates are very accurate.
Yes. It is common for a provider to revise the estimated due date after a first-trimester ultrasound, especially if it differs from the LMP-based date by more than about a week. Early ultrasound dating is generally considered more reliable than LMP dating when the two conflict. If your due date is updated, you can recalculate your timeline here using the Ultrasound method.
This Due Date Calculator is provided for educational and general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Estimated due dates are approximations based on population averages for a single pregnancy; results for twins or other multiples will differ. Always consult a qualified healthcare provider regarding your pregnancy, prenatal care, and expected delivery date.