Pregnancy Due Date Calculator
Calculate your estimated due date using medically recognized methods and track your pregnancy journey with milestones, baby size comparisons, and more
Select the first day of your most recent menstrual period
Most women have a 28-day cycle (22-44 days range). Adjust if yours differs.
Used for Mittendorf-Williams method: first-time mothers tend to carry slightly longer.
Calculate Your Due Date
Select a calculation method and enter your dates to see your estimated due date, pregnancy progress, milestones, and more.
Important
This calculator is provided for general information only and is not medical advice, diagnosis, or treatment. Results are estimates based on population averages and cannot account for your individual circumstances. Speak to a qualified healthcare professional before acting on anything you read here.
Calculate your estimated due date using medically recognized methods and track your pregnancy journey with milestones, baby size comparisons, and more
Welcome to our free Pregnancy Due Date Calculator, a comprehensive tool designed to help expectant parents estimate when their baby will arrive. Knowing your estimated due date (EDD) is one of the most important milestones in pregnancy, as it helps you and your healthcare provider plan prenatal care, monitor fetal development, and prepare for delivery. This calculator supports four medically recognized calculation methods: Last Menstrual Period (LMP) using Naegele's Rule, Conception Date, Ultrasound dating, and IVF Transfer Date. Each method is used in clinical practice, and your doctor may use one or more of these approaches to determine your due date. The most common method is based on your Last Menstrual Period (LMP), which uses Naegele's Rule to estimate your due date by adding 280 days (40 weeks) to the first day of your last period. This method also accounts for cycle length variations, since not everyone has a standard 28-day cycle. If your cycle is shorter or longer, the calculator adjusts accordingly to provide a more accurate estimate. For those who know their exact conception date, the Conception Date method adds 266 days (38 weeks) from conception, since fertilization typically occurs about 14 days after the start of your last period. This can be particularly useful for women who tracked ovulation or had fertility treatments. Ultrasound dating is considered highly accurate, especially when performed in the first trimester. By entering the date of your ultrasound and the gestational age measured at that time, the calculator can determine your due date with precision. Many healthcare providers consider early ultrasound measurements to be the gold standard for dating a pregnancy. For IVF pregnancies, the calculator uses the embryo transfer date and the age of the embryo at transfer (Day 3, Day 5, or Day 6) to calculate the due date. This method is extremely precise because the exact timing of fertilization is known. Beyond simply calculating your due date, this tool provides a wealth of information to help you track your pregnancy journey. You will see your current gestational age in weeks and days, which trimester you are in, a visual progress chart showing how far along you are, and a fun baby size comparison that tells you what fruit or vegetable your baby is the size of this week. The pregnancy milestones timeline shows key dates throughout your pregnancy, from when you might first hear the heartbeat to important prenatal screenings and tests. You can also see your baby's predicted zodiac sign and birthstone based on the estimated due date. Please remember that only about 5% of babies are born on their exact due date. Most healthy pregnancies result in delivery within a window of 37 to 42 weeks. Your due date is an estimate, and your healthcare provider is the best resource for monitoring your pregnancy and delivery timing. All calculations are performed in your browser, and no personal data is stored or transmitted.
Understanding Pregnancy Due Date Calculation
A typical pregnancy lasts about 280 days (40 weeks) from the first day of the last menstrual period, or about 266 days (38 weeks) from conception. Due dates are estimates based on averages, and only about 5% of babies arrive on their exact due date.
Naegele's Rule (LMP Method)
The most widely used method, Naegele's Rule adds 280 days to the first day of your last menstrual period. For cycles that differ from 28 days, the formula adjusts by adding or subtracting the difference. For example, a 30-day cycle adds 2 extra days, while a 26-day cycle subtracts 2 days.
Ultrasound and IVF Methods
Ultrasound dating uses measurements taken during an ultrasound scan combined with the known gestational age at that time. IVF dating is the most precise method because the exact date of fertilization is known. Day 3 embryos add 263 days, Day 5 embryos add 261 days, and Day 6 embryos add 260 days from the transfer date.
Formulas
Naegele's Rule (LMP Method)
EDD = LMP + 280 days
The standard formula used by healthcare providers. Adds 280 days (40 weeks) to the first day of the last menstrual period, assuming a 28-day cycle. For irregular cycles, adjust by adding (cycle length - 28) days.
Modified Naegele's Rule (Irregular Cycles)
EDD = LMP + 280 days + (Cycle Length - 28)
Adjusts Naegele's Rule for women with cycles shorter or longer than 28 days. A 32-day cycle adds 4 extra days; a 25-day cycle subtracts 3 days from the standard estimate.
Conception-Based Calculation
EDD = Conception Date + 266 days
Adds 266 days (38 weeks) from the known or estimated date of conception. Useful when ovulation tracking or fertility treatments provide a known fertilization date.
IVF Transfer Calculation
EDD = Transfer Date + (280 - Embryo Age - 14) days
For IVF pregnancies: Day 3 transfer adds 263 days, Day 5 adds 261 days, Day 6 adds 260 days. The most precise method since the exact fertilization date is known.
Reference Tables
Pregnancy Trimesters and Key Milestones
The three trimesters of pregnancy with their week ranges and major developmental milestones.
| Trimester | Weeks | Key Milestones |
|---|---|---|
| First | 1–12 | Positive test (week 4), heartbeat detectable (week 6), major organs forming, NT scan (week 10–13) |
| Second | 13–27 | Anatomy scan (week 18–22), first movements felt (week 18–20), viability milestone (week 24), glucose test (week 24–28) |
| Third | 28–40+ | Rapid brain development, GBS test (week 35–37), early term (week 37), full term (week 39), due date (week 40) |
Fetal Development Size by Week
Approximate fetal size at key gestational weeks, measured as crown-to-rump length (early) or head-to-heel length (later).
| Week | Size | Comparable To | Weight |
|---|---|---|---|
| 8 | 1.6 cm (0.6 in) | Kidney bean | ~1 g |
| 12 | 5.4 cm (2.1 in) | Lime | ~14 g |
| 16 | 11.6 cm (4.6 in) | Avocado | ~100 g |
| 20 | 25.6 cm (10.1 in) | Banana | ~300 g |
| 24 | 30 cm (11.8 in) | Ear of corn | ~600 g |
| 28 | 37.6 cm (14.8 in) | Eggplant | ~1,000 g |
| 32 | 42.4 cm (16.7 in) | Jicama | ~1,700 g |
| 36 | 47.4 cm (18.7 in) | Romaine lettuce | ~2,600 g |
| 40 | 51.2 cm (20.2 in) | Watermelon | ~3,400 g |
Worked Examples
Due Date from Last Menstrual Period (28-day cycle)
A woman's last menstrual period started on January 15, 2026, and she has a regular 28-day cycle.
Apply Naegele's Rule: January 15 + 280 days
Count forward: January (16 days remaining) + February (28) + March (31) + April (30) + May (31) + June (30) + July (31) + August (31) + September (30) + October (22 days) = 280 days
Estimated due date: October 22, 2026
Estimated conception date: January 15 + 14 days = January 29, 2026
Delivery window: Early term October 8 (37 weeks) to post-term November 5 (42 weeks)
Estimated due date is October 22, 2026. The baby will most likely arrive between October 8 and November 5, 2026.
Due Date from Conception Date
A woman knows she conceived on March 10, 2026, based on ovulation tracking.
Apply conception formula: March 10 + 266 days
Count forward 266 days from March 10
Estimated due date: December 1, 2026
Current gestational age adds 14 days (LMP equivalent): conception is considered week 2 day 0
Estimated due date is December 1, 2026. Gestational age at conception is counted as 2 weeks 0 days (since gestational age counts from the theoretical LMP).
Due Date with a 35-Day Cycle
A woman's LMP was February 1, 2026, and her average cycle length is 35 days (7 days longer than standard).
Standard Naegele's: February 1 + 280 = November 8, 2026
Cycle adjustment: 35 - 28 = +7 days
Modified due date: November 8 + 7 = November 15, 2026
Estimated ovulation: February 1 + 21 days (35 - 14) = February 22, 2026
Adjusted due date is November 15, 2026 — one week later than the standard calculation because her longer cycle means ovulation occurs later.
How to Use the Pregnancy Due Date Calculator
Choose Your Calculation Method
Select from four medically recognized methods: Last Menstrual Period (most common), Conception Date (if you know when conception occurred), Ultrasound (using measurements from an ultrasound scan), or IVF Transfer Date (for in vitro fertilization pregnancies). You can also use the Reverse mode to plan a conception date around a desired due date.
Enter Your Dates and Details
For the LMP method, enter the first day of your last period and adjust your average cycle length if it differs from 28 days. For Conception Date, enter the date you believe conception occurred. For Ultrasound, enter the scan date and measured gestational age. For IVF, enter your transfer date and select the embryo age (Day 3, Day 5, or Day 6).
Calculate and Review Your Results
Click Calculate Due Date to see your estimated due date prominently displayed, along with your current gestational age, trimester, days remaining, and the likely delivery window (37-42 weeks). Scroll down to see your pregnancy progress chart, baby size comparison, and milestones timeline.
Explore Additional Details
Review the trimester dates, key prenatal appointments, your baby's predicted zodiac sign and birthstone, and the full pregnancy milestones timeline. You can export your results to CSV or print them to share with your healthcare provider. Remember that due dates are estimates, and always consult your doctor.
Frequently Asked Questions
How accurate is a pregnancy due date calculator?
Pregnancy due date calculators provide a good estimate, but only about 5% of babies are born on their exact estimated due date. Most babies arrive within a two-week window around the due date, with the majority born between 37 and 42 weeks of gestation. The accuracy depends on the calculation method used. Ultrasound dating in the first trimester is considered the most accurate, typically within 5-7 days of the actual delivery date. The LMP method using Naegele's Rule assumes a regular 28-day cycle, so accuracy improves when you adjust for your actual cycle length. IVF dates are extremely precise since the exact fertilization timing is known. Your healthcare provider may adjust your due date based on ultrasound measurements taken during your first prenatal visit.
What is Naegele's Rule and how does it calculate my due date?
Naegele's Rule is the standard formula used by healthcare providers to estimate a pregnancy due date. It works by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes that conception occurs approximately 14 days after the start of your period, based on a 28-day menstrual cycle. If your cycle length differs from 28 days, the formula is adjusted by adding or subtracting the difference. For example, if you have a 32-day cycle, 4 extra days are added to the standard 280 days. While simple and widely used, Naegele's Rule has limitations because it assumes regular cycles and a consistent 14-day follicular phase. Your doctor may use ultrasound dating to refine the estimate if needed.
Can my due date change during pregnancy?
Yes, your due date can change, and this is relatively common. The most frequent reason for a due date change is when an early ultrasound measurement differs significantly from the date calculated using your last menstrual period. If the ultrasound estimate differs by more than 7 days in the first trimester or more than 10-14 days in the second trimester, your healthcare provider may adjust your due date to match the ultrasound measurements. Other factors that may lead to a due date change include irregular menstrual cycles that made the initial LMP calculation less reliable, or if you were unsure about the exact date of your last period. Once a due date is established by a first-trimester ultrasound, it typically remains unchanged for the rest of the pregnancy.
What is the difference between gestational age and fetal age?
Gestational age and fetal age are two different ways to measure how far along a pregnancy is. Gestational age is counted from the first day of the last menstrual period (LMP), which is about two weeks before conception actually occurs. This means gestational age is always approximately two weeks more than the actual age of the embryo or fetus. Fetal age (also called embryonic age or conceptional age) counts from the actual date of fertilization. So when your doctor says you are 10 weeks pregnant, that is the gestational age, and the fetus is actually about 8 weeks old. Most pregnancy timelines, due date calculations, and prenatal care schedules use gestational age as the standard measurement. The 40-week pregnancy duration refers to gestational age.
What does full-term pregnancy mean and when is it safe to deliver?
The American College of Obstetricians and Gynecologists (ACOG) defines pregnancy terms as follows: Early term is 37 weeks through 38 weeks and 6 days, full term is 39 weeks through 40 weeks and 6 days, late term is 41 weeks through 41 weeks and 6 days, and post-term is 42 weeks and beyond. A baby born at full term (39+ weeks) has had the optimal time for brain, lung, and liver development. While babies born at 37-38 weeks are generally healthy, research shows that waiting until at least 39 weeks reduces risks of breathing problems, feeding difficulties, and NICU admissions. Delivery is not typically induced before 39 weeks unless there are medical complications. Your healthcare provider will monitor your pregnancy closely as you approach and pass your due date.
How is the due date calculated for IVF pregnancies?
IVF (in vitro fertilization) due dates are calculated differently because the exact timing of fertilization is known. For IVF pregnancies, the calculation starts from the embryo transfer date and adds the number of days to reach a full 280-day (40-week) gestational period, minus the embryo's age at transfer plus 14 days. For a Day 3 embryo transfer, the due date is the transfer date plus 263 days. For a Day 5 blastocyst transfer, it is the transfer date plus 261 days. For a Day 6 transfer, it is 260 days. The logic is that a Day 3 embryo has a gestational age of 17 days at transfer (3 days embryo age plus 14 days from theoretical LMP to ovulation), so 280 minus 17 equals 263 days remaining. IVF dating is considered the most accurate method since the exact fertilization date is known.
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