Enter your estimated due date to calculate your pregnancy timeline.
Enter the first day of your last menstrual period and your average cycle length.
Enter your ultrasound date and the gestational age shown on the scan.
Enter the date of conception (fertilization) to calculate your due date and schedule.
Enter your embryo transfer date and the age of the embryo at the time of transfer.
A pregnancy calculator is an online tool that helps expectant parents determine key dates and milestones throughout a pregnancy. By entering a known reference point — such as the due date, the first day of the last menstrual period, an ultrasound measurement, the conception date, or an IVF transfer date — the calculator works backwards and forwards to establish the entire pregnancy timeline. The result is a personalized week-by-week schedule showing when each trimester begins and ends, when key developmental milestones occur, and exactly when the baby is expected to arrive.
Pregnancy calculators are used by millions of women and couples around the world because they translate a single date into an actionable plan. Knowing your gestational age, your current trimester, and when to schedule prenatal appointments removes a great deal of uncertainty from what can be an emotionally overwhelming time. While no calculator replaces the guidance of a licensed obstetrician or midwife, having this information at your fingertips empowers you to ask better questions and prepare more effectively for each stage of your pregnancy.
Pregnancy is measured in gestational weeks, which count from the first day of the last menstrual period (LMP) rather than from the actual date of conception. This may seem counterintuitive — after all, no conception has taken place in week one — but it is the universal standard in obstetrics because the LMP is a known, observable event while the exact moment of conception is rarely known with certainty. Under this convention, a typical pregnancy lasts 40 weeks (280 days) from the LMP to the estimated due date (EDD).
The formula that underpins all standard pregnancy date calculations is Naegele's Rule, developed in the early 19th century by German obstetrician Franz Karl Naegele. The rule states: 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. Mathematically, this is equivalent to adding 280 days to the LMP — which is exactly what our calculator does. For cycles that differ from the standard 28 days, the calculator adjusts by adding the difference between your actual cycle length and 28 to shift the estimated ovulation and conception date accordingly.
If you already know your estimated due date — perhaps from a previous visit to your healthcare provider — this is the simplest starting point. The calculator subtracts 280 days from the EDD to determine the equivalent LMP, then builds the full schedule from there. The conception date is estimated as 14 days after the adjusted LMP (corresponding to the typical ovulation window in a 28-day cycle). This method is ideal when you have a confirmed due date but want to explore the full week-by-week timeline in more detail.
The LMP method is the most widely used approach in clinical practice. You enter the first day of your most recent menstrual period and your average cycle length. For cycles of exactly 28 days, the estimated due date is simply LMP plus 280 days. For longer or shorter cycles, the calculator adjusts the timing of ovulation — which occurs approximately 14 days before the next expected period — and shifts the due date accordingly. For example, a 35-day cycle places ovulation on day 21 rather than day 14, moving the EDD seven days later than the standard calculation would suggest. Cycle lengths between 22 and 44 days are supported.
An obstetric ultrasound (sonogram) is one of the most accurate ways to date a pregnancy, particularly when performed in the first trimester (before 14 weeks). The sonographer measures the embryo's crown-rump length (CRL) or other biometric parameters and reports the gestational age in weeks and days. You enter the date of the ultrasound and the gestational age it indicated, and the calculator works backwards to determine the corresponding LMP and forward to establish the due date. First-trimester ultrasound dating is accurate to within five to seven days, making it more precise than LMP-based dating when the LMP is uncertain or cycles are irregular.
If you know approximately when you conceived — for instance, if you were tracking ovulation with an ovulation predictor kit, basal body temperature monitoring, or fertility charting — you can enter that date directly. The calculator adds 266 days (38 weeks) to the conception date to determine the EDD. It also estimates the LMP as 14 days before conception to align with the standard gestational age convention. This method is particularly useful for women with very regular cycles who have a reliable sense of their ovulation window.
For pregnancies achieved through in vitro fertilization (IVF), the date of embryo transfer is precisely known. The calculator adjusts for the age of the embryo at transfer — day 3, day 5, or day 6 — to determine the equivalent fertilization (conception) date. From there, it adds 266 days to the conception date to produce the EDD. Because IVF timelines are controlled and documented in detail, this method produces highly accurate due date estimates, often matching ultrasound dating very closely.
Gestational age is expressed in weeks and days counted from the first day of the last menstrual period. When a healthcare provider says a patient is "eight weeks pregnant," they mean eight weeks have elapsed since the LMP — even though actual fertilization occurred roughly six weeks earlier. This means that at the moment of conception, you are already considered to be approximately two weeks pregnant in gestational terms.
Gestational age is important because nearly all clinical guidelines for prenatal testing, screening windows, and intervention thresholds are expressed in gestational weeks. Knowing your precise gestational age allows you to schedule first-trimester screening (typically between weeks 11 and 13), the anatomy scan (around week 20), glucose tolerance testing (weeks 24–28), and group B streptococcus screening (weeks 35–37) at the optimal times for accuracy and clinical usefulness.
The first trimester encompasses the most dramatic developmental changes of the entire pregnancy. During weeks 1 and 2, the body prepares for ovulation while the uterine lining thickens. Fertilization typically occurs in week 2 (day 14 of a 28-day cycle), and the fertilized egg travels through the fallopian tube toward the uterus. By week 3, implantation takes place and the embryo begins producing human chorionic gonadotropin (hCG), the hormone detected by home pregnancy tests. By week 4, hCG levels are usually high enough for a home test to read positive.
Week 6 is a landmark moment: the embryonic heartbeat becomes detectable by transvaginal ultrasound. Between weeks 6 and 10, all major organ systems begin forming — the heart, brain, spinal cord, limbs, and facial features all take shape during this critical organogenesis window. By the end of the first trimester (week 12), the fetus is fully formed in miniature, measuring about 2.5 inches from crown to rump. The risk of miscarriage drops significantly after week 13 as the placenta takes over hormone production and the embryonic period gives way to the fetal period.
Common first-trimester experiences include nausea and vomiting (morning sickness), breast tenderness, fatigue, frequent urination, and heightened sensitivity to smells. These symptoms are driven primarily by rising hCG and progesterone levels. Although the pregnancy is not yet visible externally, the physiological changes underway are profound.
The second trimester is widely regarded as the most comfortable period of pregnancy. Nausea typically subsides, energy levels improve, and the pregnancy begins to show visibly. This is also a period of rapid fetal growth and development. By week 16, the fetus begins making small movements, though these are not yet felt by the mother. By week 18, movements become more pronounced and are often described as "fluttering" or "quickening." Around this same time, a detailed anatomy scan can typically identify the baby's sex and assess organ development.
Week 20 marks the halfway point of pregnancy. By this stage, the fetus is covered in a protective waxy coating called vernix caseosa and is developing eyebrows and fingernails. The mother's abdomen is now clearly visible, and many couples choose to announce the pregnancy publicly during the second trimester. Week 23 is a significant viability threshold: babies born at this gestational age have a chance of survival with intensive neonatal care, though outcomes vary considerably. Viability increases substantially with each passing week from this point forward.
The third trimester is characterized by rapid weight gain — both for the fetus and the mother — and increasing physical discomfort as the growing baby presses against internal organs. By week 28, the baby can open its eyes, respond to light and sound, and breathe amniotic fluid in and out of its lungs in preparation for air breathing after birth. From this point, the main task is continued growth and maturation, particularly of the lungs, brain, and immune system.
Week 37 marks the threshold for "full term." Babies born between weeks 37 and 38 are considered early term; those born between weeks 39 and 40 are full term; those born between weeks 41 and 42 are late term; and those born after 42 weeks are post-term. The due date falls at week 40, but only about 5% of babies are born exactly on their due date. Most births occur within two weeks before or after the EDD, meaning a delivery window of roughly weeks 38 to 42 is entirely normal.
Third-trimester symptoms include back pain, shortness of breath, frequent urination (as the baby descends into the pelvis), Braxton Hicks contractions, ankle swelling, and disrupted sleep. Healthcare visits become more frequent in this trimester, typically every two weeks from weeks 28 to 36 and then weekly from week 36 until delivery.
The following milestones are embedded in the pregnancy schedule table generated by our calculator:
Consistent prenatal care is one of the most important investments you can make in both your health and your baby's health. Most healthcare providers recommend the following general schedule, though individual needs vary:
As the due date approaches, knowing the signs of true labor versus false labor (Braxton Hicks contractions) is important. True labor contractions become progressively longer, stronger, and closer together — typically following a pattern of five minutes apart, lasting one minute, for one hour (the "5-1-1 rule"). Other signs that labor may be beginning include the release of the mucus plug (a blood-tinged discharge), rupture of membranes (the "water breaking"), and increasing pelvic pressure as the baby descends.
Contact your healthcare provider or go to the hospital if contractions are following the 5-1-1 pattern, if your water breaks, if you notice significant bleeding, if the baby's movements suddenly decrease, or if you experience severe headaches, blurred vision, or sudden swelling — all of which can indicate preeclampsia and require immediate evaluation.
The EDD is an estimate, not a guarantee. Only about 4–5% of babies are born on their exact due date. Around 70% of births occur within 10 days of the EDD, and the vast majority occur within two weeks. The most accurate dating method is a first-trimester ultrasound (before 14 weeks), which can pinpoint gestational age within 5–7 days. LMP-based dating is less precise because it assumes a 28-day cycle and consistent ovulation on day 14, neither of which applies to all women.
Our calculator adjusts automatically for cycle lengths between 22 and 44 days. The adjustment works by shifting the estimated ovulation date — which occurs approximately 14 days before the next expected period, regardless of cycle length. For a 35-day cycle, ovulation occurs around day 21 rather than day 14, so the due date is shifted seven days later than a standard 28-day calculation would suggest.
A first-trimester ultrasound is generally the most accurate dating method, particularly for women with irregular cycles or uncertain LMP dates. When performed before 14 weeks, ultrasound dating is accurate to within 5–7 days. LMP-based dating is accurate for women with regular 28-day cycles and a known LMP date. IVF dating is extremely precise because the exact day of fertilization is known. The due date method is simply the reverse of LMP dating — equally accurate if the original EDD was established by ultrasound.
Gestational age counts from the first day of the last menstrual period and is the standard measurement used in obstetrics. Fetal age (also called embryonic age or fertilization age) counts from the actual moment of conception, which typically occurs about 14 days after the LMP in a 28-day cycle. Fetal age is therefore approximately two weeks less than gestational age. When a doctor or calculator says you are "8 weeks pregnant," they mean 8 weeks gestational age — the embryo itself is only about 6 weeks old in terms of fetal age.
It is common for healthcare providers to revise the estimated due date after a first-trimester ultrasound, particularly if there is a discrepancy of more than seven days from the LMP-based date. If the ultrasound date is different from your original EDD, use our Ultrasound tab to recalculate your schedule based on the sonogram measurements. Early ultrasound dating is generally considered more reliable than LMP dating when there is a conflict between the two, especially for women with irregular cycles.
For IVF pregnancies, the due date is calculated from the date of embryo transfer and the age of the embryo at the time of transfer. For a day-5 transfer (blastocyst), the conception date is estimated as five days before the transfer date, and the EDD is 266 days (38 weeks) after conception. For a day-3 transfer, the calculator subtracts three days from the transfer date. For a day-6 transfer, it subtracts six days. The IVF method is highly accurate because every step of the fertilization and transfer process is precisely timed and documented.