Pregnancy Due Date Calculator
Estimate an expected due date (EDD), trimester ranges, and a simple pregnancy timeline from LMP, conception date, or IVF transfer date. Educational only, not medical advice or a substitute for prenatal care.
Estimates an expected due date, trimester ranges, and week-by-week timing based on user-entered dates. Uses simple calendar math (like counting weeks/days from a starting date). Does NOT replace ultrasound dating or advice from an OB/GYN, midwife, or other clinician. Not a diagnostic tool; only an educational estimate.
Enter Your Information
Default is 28 days if not specified.
Optional Context (For warnings only)
Default is today. Used to calculate current gestational age.
Choose a dating method and enter your dates to see an estimated due date and simple pregnancy timeline.
Estimated due date and milestones
You just got a positive pregnancy test and want to know when your baby might arrive. A pregnancy due date calculator takes your last menstrual period, adds 280 days, and hands you a target date. A common mistake is treating that date like a deadline etched in stone. Only about 5 percent of babies arrive exactly on their due date. The number gives you a reference point for scheduling prenatal visits, planning leave from work, and watching for developmental milestones along the way.
This calculator supports multiple input methods: last menstrual period (LMP), known conception date, or IVF transfer date. Enter your information, and it returns your estimated due date plus a week-by-week breakdown showing when you cross into each trimester. First trimester runs through week 12, second trimester covers weeks 13 through 27, and third trimester stretches from week 28 to delivery.
Milestones matter because they guide prenatal care. The first heartbeat often appears around week 6. Anatomy scans happen between weeks 18 and 22. Glucose screening lands around week 24 to 28. Your due date anchors all of these appointments, even though the actual birth might happen two weeks earlier or later than predicted.
How due dates are calculated
The standard formula is called Naegele's rule. Take the first day of your last menstrual period, add seven days, subtract three months, and add one year. That arithmetic lands you at 280 days, or 40 weeks, from LMP. The math assumes a 28-day cycle with ovulation on day 14, which describes many but not all women.
If your cycle runs longer or shorter than 28 days, the calculator can adjust. A 35-day cycle means ovulation likely happened around day 21 instead of day 14, pushing your due date about a week later. A 24-day cycle shifts ovulation earlier, pulling the due date forward. Enter your average cycle length, and the formula accounts for the difference.
Conception-based calculation works backward. If you know the exact date of conception, add 266 days to get your due date. IVF patients know their transfer date and embryo age precisely. A day-5 blastocyst transfer on January 15 means the embryo is already 5 days old, so the calculator counts from there. These methods remove some guesswork but still land on estimates, not guarantees.
Example: LMP -> week/day
Common scenario: A 29-year-old woman had her last period start on March 1. She has a regular 28-day cycle. Adding 280 days lands on December 6 as her estimated due date. On April 15, she is 6 weeks and 3 days pregnant. The first trimester ends around June 1 (week 12), second trimester runs through September 14 (week 27), and third trimester begins September 15. She schedules her anatomy scan for mid-July and glucose test for late August.
Edge case: A 34-year-old woman has a 35-day cycle. Her LMP was March 1, but she didn't ovulate until around March 22 instead of March 15. Without adjusting for cycle length, the calculator would predict December 6. With the 7-day adjustment, her due date shifts to December 13. On April 15, she is only 5 weeks and 3 days pregnant rather than 6 weeks 3 days. The week difference matters for early ultrasound dating, where a few days can change whether the embryo is visible or not.
These examples show why cycle length matters. A standard 28-day assumption works for many people, but anyone with longer or shorter cycles should enter their actual average to get a more accurate timeline.
Ultrasound dating vs LMP
Early ultrasounds measure the embryo from crown to rump and compare that length to standard growth charts. Between weeks 6 and 9, embryos grow at remarkably consistent rates, so crown-rump length can date a pregnancy within a few days. If the ultrasound date differs from your LMP-based date by more than a week, your provider may adjust your official due date.
Why does ultrasound sometimes trump LMP? Memory can be fuzzy. Some women spot during early pregnancy and mistake it for a light period. Irregular cycles make ovulation timing unpredictable. The ultrasound bypasses all of that by measuring the baby directly. First-trimester scans are most accurate; by the second trimester, normal variation in fetal size makes dating less precise.
If your provider gives you a different due date after an ultrasound, use that number. You can still reference your LMP-based date for personal tracking, but the ultrasound-adjusted date guides medical decisions like timing genetic screenings, monitoring fetal growth, and deciding when to induce if pregnancy goes past 41 weeks.
What to track by trimester
First trimester covers weeks 1 through 12. Key events include confirming the pregnancy, seeing the heartbeat, and completing first-trimester screening for chromosomal conditions. Many women experience nausea, fatigue, and breast tenderness during these weeks. Miscarriage risk is highest in this window, so some people wait until week 12 or 13 to share the news.
Second trimester spans weeks 13 through 27. Nausea often fades, energy returns, and the belly starts showing. The anatomy scan around week 20 checks organ development and can reveal the baby's sex. Fetal movement becomes noticeable somewhere between weeks 16 and 25, depending on placenta position and body type. Glucose screening tests for gestational diabetes between weeks 24 and 28.
Third trimester runs from week 28 to delivery. Prenatal visits become more frequent, shifting from monthly to biweekly and then weekly. Growth scans check that the baby is gaining weight on track. The baby moves into head-down position sometime after week 32 for most pregnancies. After week 37, the pregnancy is considered full term, and labor could begin any day.
Sources and references
This calculator uses Naegele's rule, a dating method introduced in the 19th century and still widely applied today. Trimester definitions and milestone timing follow guidelines from the American College of Obstetricians and Gynecologists (ACOG) and the Centers for Disease Control and Prevention (CDC).
- ACOG: How Your Fetus Grows During Pregnancy
- CDC: Pregnancy Information
- March of Dimes: Pregnancy Week by Week
Disclaimer: This calculator is for educational purposes only and does not provide medical advice. Due dates are estimates based on calendar math and general assumptions. Only about 5 percent of babies arrive on their exact due date; most come within a two-week window on either side. Ultrasound dating is often more accurate, especially in the first trimester. Always consult a qualified healthcare professional for personalized prenatal care, accurate dating, and guidance on pregnancy-related decisions.
Frequently Asked Questions
Common questions about due dates, pregnancy timelines, and using this calculator.
How accurate are due date calculators?
Due date calculators provide rough estimates based on simple calendar math. They can be helpful for general awareness, but they are not as accurate as ultrasound-based dating performed by healthcare providers. Many factors can affect accuracy, including cycle length, uncertainty about dates, and individual variations. Only about 5% of babies are born exactly on their due date—most arrive within a two-week window before or after. Healthcare providers often use early ultrasound measurements (especially in the first trimester) to refine due dates, which can be more accurate than LMP-based calculations alone. This calculator is for educational purposes only and should not replace your healthcare provider's due date, especially if it's based on ultrasound measurements.
Why is my doctor's due date different from this one?
There are several reasons why your healthcare provider's due date might differ from a calculator estimate: (1) Your provider may have used early ultrasound measurements, which can be more accurate than LMP-based calculations, especially if your cycle length is irregular or uncertain. Ultrasound dating measures fetal size directly and doesn't depend on knowing your exact LMP or cycle length. (2) Your provider considers your complete medical history, physical examination findings, and any complications. (3) Different calculation methods (LMP, conception date, IVF, ultrasound) can produce slightly different estimates, often varying by a few days to a week. Your healthcare provider's due date should always take priority over calculator estimates. This tool is for educational awareness only.
Can this tool tell me if my pregnancy is healthy?
No. This calculator only provides simple calendar-based date estimates. It cannot assess pregnancy health, fetal development, viability, or any medical conditions. It cannot diagnose complications, predict outcomes, or provide medical reassurance. Pregnancy health and fetal development are assessed through prenatal care, including physical examinations, ultrasounds, blood tests, and other medical evaluations performed by healthcare providers. If you have concerns about your pregnancy health, symptoms (such as severe abdominal pain, heavy bleeding, decreased fetal movement), or fetal development, please discuss them with your healthcare provider immediately. This tool is for educational purposes only and does not provide medical advice or diagnosis.
What if I'm not sure of my LMP?
If you're not sure of your last menstrual period (LMP), the calculator's estimate may be less accurate. In this case, your healthcare provider will likely use early ultrasound measurements to determine your due date, which can be more accurate than LMP-based calculations when the LMP is uncertain. Ultrasound dating doesn't depend on knowing your exact LMP or cycle length—it measures fetal size directly. If you're using this calculator and are uncertain about your LMP, consider using the 'Known Due Date (from clinician)' option if your provider has already given you a due date, or wait until you have an ultrasound-based due date from your provider. This tool is for educational awareness only.
How does IVF dating work compared to LMP dating?
IVF pregnancies have a known transfer date and gestational age at transfer, which makes dating more precise than LMP-based calculations. For IVF, the gestational age at transfer depends on the embryo stage (day 3, day 5, or day 6) and whether it was a fresh or frozen transfer. Day 5 embryos (blastocysts) typically have a gestational age of about 19 days at transfer, while day 3 embryos have a gestational age of about 16 days. The calculator works backwards from the transfer date using the known gestational age at transfer to estimate an LMP-equivalent date, then adds 280 days to get the due date. However, your fertility clinic or healthcare provider will provide the most accurate due date based on their specific protocols and any early ultrasound measurements. This calculator is for educational purposes only and should not replace your provider's due date.
What if my cycle is longer or shorter than 28 days?
If your menstrual cycle is longer or shorter than the standard 28 days, you can enter your average cycle length in the calculator for more accurate LMP-based calculations. Longer cycles (35+ days) may result in later due dates, while shorter cycles (21-25 days) may result in earlier due dates. The calculator adjusts the LMP date based on your cycle length before calculating the due date. However, if you have irregular cycles, LMP-based calculations may still be less accurate, and ultrasound dating is often more reliable. Ultrasound dating doesn't depend on cycle length—it measures fetal size directly. If you have irregular cycles, your healthcare provider will likely use ultrasound measurements to determine your due date.
Can I use this for multiple pregnancies (twins, triplets)?
The calculator can provide general estimates for multiple pregnancies, but multiple pregnancies may have different due dates and often deliver earlier than singleton pregnancies. Twins typically deliver around 36-37 weeks, while triplets may deliver even earlier. The calculator provides warnings for multiple pregnancies, but it cannot fully account for the unique characteristics of multiple pregnancies, which require specialized monitoring and care. Always follow your healthcare provider's due date and recommendations for multiple pregnancies, as they consider the specific needs of multiple pregnancies, including more frequent monitoring, potential complications, and delivery planning. This calculator is for educational purposes only and should not replace your provider's guidance for multiple pregnancies.
What percentage of babies are born on their due date?
Only about 5% of babies are born exactly on their due date. Most babies (about 80%) are born within a two-week window before or after the due date (between 38 and 42 weeks). About 10% of babies are born before 37 weeks (preterm), and about 10% are born after 42 weeks (post-term). Due dates are estimates, not exact predictions, and many factors can affect when labor begins, including individual variation, medical factors, and natural variation in pregnancy length. Don't stress if your baby doesn't arrive exactly on the due date—this is normal and expected. Use the due date as a reference point for planning, not a guarantee. Your healthcare provider will monitor your pregnancy and discuss delivery timing based on your individual circumstances.