Pregnancy Calculator — Free Due Date Estimator
Estimate your due date, track your current pregnancy week and trimester, and see key milestone dates based on your last menstrual period and cycle length using Naegele's rule.
Key Milestones
Pregnancy Progress
Estimated Due Date
Wednesday, May 6, 2026
Current Week
30w 0d
Trimester
3/rd
Summary: Based on your last menstrual period of Wednesday, July 30, 2025 with a 28-day cycle, your estimated due date is Wednesday, May 6, 2026. You are currently 30 weeks and 0 days into your pregnancy (Trimester 3). This is an estimate only. Your healthcare provider will confirm your due date with an ultrasound.
How to Use the Pregnancy Calculator
- Enter the first day of your last menstrual period (LMP): Click the date picker and select or type the date when your most recent menstrual period started. This is not the date your period ended, but the first day of bleeding. If you are unsure of the exact date, use your best estimate. The calculator allows dates within the past 300 days, covering the full range of a possible pregnancy. This date is the foundation for all calculations, as standard pregnancy dating begins from the LMP.
- Adjust your average cycle length: Enter the typical length of your menstrual cycle in days. The default is 28 days, which is the average cycle length used in standard pregnancy dating. If your cycles are consistently shorter (such as 25 days) or longer (such as 33 days), adjusting this value will refine your due date estimate. The calculator accepts cycle lengths from 20 to 45 days. If your cycles are irregular (varying by more than 7 days), use the average of your last three cycles for the best estimate.
- Review your pregnancy progress and milestones: The results panel instantly displays your estimated due date, current pregnancy week and day (e.g., 24 weeks 3 days), which trimester you are in, the number of days remaining until your due date, and a percentage completion. A color-coded progress bar visually represents your journey through all three trimesters. The milestone panel shows the dates marking the end of each trimester for easy reference.
All results update instantly when you change any input. Share these estimates with your healthcare provider, who may adjust the due date based on ultrasound measurements. Remember that the estimated due date is just that — an estimate. Only about 4% of babies are born on their exact due date, and a normal delivery can occur from 37 to 42 weeks gestation.
Due Date Calculation Formula
Naegele's Rule (standard):
Due Date = LMP + 280 days Adjusted for cycle length:
Due Date = LMP + 280 + (Cycle Length - 28) days Current Week = Days Since LMP / 7 Variables Explained
- Last Menstrual Period (LMP): The first day of your most recent menstrual period. This serves as the starting point for gestational age calculation because it is an observable date, unlike conception which is typically unknown. Standard pregnancy dating starts from this date, meaning you are considered approximately 2 weeks pregnant at the time of conception.
- 280 days (40 weeks): The standard duration of human pregnancy from LMP to delivery. This includes approximately 2 weeks before conception (the follicular phase of the menstrual cycle) and 38 weeks of actual fetal development. The 280-day figure represents the median duration and was established through observation of thousands of pregnancies.
- Cycle Length Adjustment: For cycles other than 28 days, the formula adjusts the due date. Longer cycles imply later ovulation, so days are added. Shorter cycles imply earlier ovulation, so days are subtracted. For a 32-day cycle, ovulation likely occurs on day 18 instead of day 14, adding 4 days to the due date.
- Trimester Calculation: First trimester spans weeks 1-12, second trimester weeks 13-27, and third trimester weeks 28-40. These divisions roughly correspond to major developmental phases and help organize prenatal care schedules.
- Progress Percentage: Calculated as (days since LMP / total expected days) x 100. This provides an intuitive measure of how far along the pregnancy has progressed toward the estimated due date.
Step-by-Step Example
Calculate the due date for someone with an LMP of June 1, 2025, and a 30-day cycle:
- Start with the LMP date: June 1, 2025
- Add standard gestation: 280 days
- Adjust for cycle length: 30 - 28 = +2 days
- Total days to add: 280 + 2 = 282 days
- Due date: June 1, 2025 + 282 days = March 10, 2026
- If today is October 15, 2025 (136 days since LMP): Week 19, Day 3
- Trimester: 2nd (week 19 falls between weeks 13-27)
- Days remaining: 282 - 136 = 146 days
- Progress: (136 / 282) x 100 = 48.2% complete
This tells the expecting parent that they are about halfway through their pregnancy, in the second trimester, with approximately 146 days (about 4.8 months) until the estimated due date. The 2-day cycle adjustment shifted the due date from March 8 to March 10.
Practical Examples
Example 1: Amanda's First Pregnancy
Amanda, a 29-year-old first-time mother, has regular 28-day cycles. Her LMP was August 15, 2025. She discovered she was pregnant in mid-September and wants to know her due date and current progress (as of February 14, 2026).
- Due Date: August 15, 2025 + 280 days = May 22, 2026
- Days since LMP: 183 days
- Current week: 26 weeks, 1 day
- Trimester: 2nd (approaching 3rd trimester at week 28)
- Days remaining: 97 days
- Progress: 65.4% complete
Amanda is approximately two-thirds through her pregnancy and approaching the third trimester. Her healthcare provider has scheduled her anatomy scan, glucose tolerance test, and Group B strep screening based on these dates. She shares the due date with her employer to plan maternity leave starting around May 8, giving her two weeks before the due date to prepare.
Example 2: Rachel with a Longer Cycle
Rachel, a 33-year-old, has consistently longer cycles averaging 35 days. Her LMP was July 1, 2025. She wants to understand how her longer cycle affects the due date.
- Standard due date (28-day cycle): July 1 + 280 = April 7, 2026
- Adjusted due date (35-day cycle): July 1 + 287 = April 14, 2026
- Difference: 7 days later
- As of Feb 14, 2026: Week 32, Day 4 (adjusted)
- Trimester: 3rd
- Days remaining: 59 days
The 7-day adjustment is significant because it places Rachel a full week earlier in her pregnancy than a standard calculation would suggest. Without this adjustment, her provider might consider scheduling interventions (like induction) earlier than necessary. Rachel's 12-week ultrasound confirmed the adjusted date was more accurate, falling within 3 days of the ultrasound-based estimate. This shows why reporting your actual cycle length to your healthcare provider is important for accurate dating.
Example 3: Jennifer Planning Around Work
Jennifer is a 36-year-old project manager. Her LMP was September 20, 2025, with a 26-day cycle. She needs to plan project handoffs, maternity leave, and childcare arrangements well in advance.
- Adjusted due date: September 20 + 278 days = June 25, 2026
- End of 1st trimester: December 20, 2025
- End of 2nd trimester: April 4, 2026
- As of Feb 14, 2026: Week 21, Day 1
- Planning buffer: Start handoffs by June 1, 2026
Jennifer uses the milestone dates to create a detailed timeline. She announces at work at the end of her first trimester (December 2025), begins training her replacement in April 2026, completes all project handoffs by early June, and starts maternity leave on June 11 — two weeks before her due date. The date calculator helps her count business days for scheduling meetings and deadlines during this transition period.
Example 4: Twins and High-Risk Monitoring
Maria, a 31-year-old expecting twins, has an LMP of October 5, 2025, with a 28-day cycle. While the calculator provides the standard singleton due date, twin pregnancies require different expectations.
- Standard due date: October 5 + 280 = July 12, 2026
- Average twin delivery: 36-37 weeks (around June 28 to July 5, 2026)
- As of Feb 14, 2026: Week 18, Day 6
- Trimester: 2nd
Maria's OB-GYN explains that while the calculator correctly estimates 40 weeks, twin pregnancies typically deliver earlier. The average twin delivery occurs at 36-37 weeks, and ACOG recommends delivery of uncomplicated dichorionic-diamniotic twins at 38 weeks. Maria uses the calculator's milestone dates as a framework but works closely with her maternal-fetal medicine specialist for a personalized delivery plan. Her more frequent prenatal visits begin at 28 weeks for additional monitoring. This example illustrates that while the calculator provides an excellent baseline, individual circumstances always require professional medical guidance.
Pregnancy Week-by-Week Development Reference
| Week | Trimester | Baby Size | Key Development |
|---|---|---|---|
| Week 4 | 1st | Poppy seed | Implantation complete, positive pregnancy test |
| Week 8 | 1st | Raspberry | All major organs forming, heartbeat detectable |
| Week 12 | 1st | Lime | End of 1st trimester, miscarriage risk drops significantly |
| Week 16 | 2nd | Avocado | Gender may be visible, first movements possible |
| Week 20 | 2nd | Banana | Halfway point, anatomy scan, movements felt regularly |
| Week 24 | 2nd | Ear of corn | Viability milestone, lungs developing surfactant |
| Week 28 | 3rd | Eggplant | 3rd trimester begins, eyes can open, sleep-wake cycles |
| Week 32 | 3rd | Squash | Rapid brain growth, practicing breathing movements |
| Week 36 | 3rd | Honeydew melon | Lungs nearly mature, head may engage in pelvis |
| Week 40 | 3rd | Watermelon | Full term, average weight 7.5 lbs, ready for delivery |
Tips and Complete Guide to Pregnancy Tracking
Understanding Due Date Accuracy and Expectations
While the due date is presented as a single date, it is more accurate to think of it as the center of a "due window." About 80% of babies are born within 2 weeks of the estimated due date — either before or after. First-time mothers tend to deliver a few days after their due date on average, while subsequent pregnancies may deliver slightly earlier. The due date serves as an important reference point for scheduling prenatal care, monitoring fetal growth, and making plans, but flexibility in expectations is key. Discuss with your healthcare provider what to expect as you approach and potentially pass your due date.
Prenatal Care Timeline
Knowing your current week helps you stay on track with recommended prenatal care. Schedule your first prenatal visit as soon as you know you are pregnant, ideally between weeks 6 and 8. Key screening tests include first-trimester screening (weeks 11-14), cell-free DNA testing (available from week 10), the anatomy ultrasound (weeks 18-22), glucose tolerance test (weeks 24-28), and Group B streptococcus screening (weeks 35-37). Your provider may schedule additional monitoring based on your individual risk factors, age, and health history. Use the milestone dates from the calculator to plan ahead for these appointments.
Nutrition and Weight Gain During Pregnancy
Calorie needs increase during pregnancy, but not as dramatically as the old "eating for two" saying suggests. During the first trimester, no additional calories are typically needed. In the second trimester, approximately 340 extra calories per day are recommended, increasing to about 450 extra calories in the third trimester. Total recommended weight gain depends on your pre-pregnancy BMI: 25-35 pounds for normal weight, 15-25 pounds for overweight, and 11-20 pounds for obese BMI. Our calorie calculator can help establish your baseline needs, though you should work with your healthcare provider to determine pregnancy-specific targets. Key nutrients include folic acid (600mcg daily), iron (27mg), calcium (1000mg), and DHA omega-3 fatty acids.
Planning and Preparation by Trimester
Each trimester brings different preparation priorities. In the first trimester, focus on finding a healthcare provider, starting prenatal vitamins, and adjusting lifestyle habits. The second trimester is ideal for setting up the nursery, taking childbirth education classes, creating a birth plan, and beginning to research childcare options. The third trimester is the time to install the car seat, pack the hospital bag (by week 36), finalize maternity leave plans, pre-register at the hospital, and choose a pediatrician. Having key dates from this calculator helps you map these tasks to specific timeframes so nothing is left to the last minute.
Common Mistakes to Avoid
- Using the end date of your period instead of the start date: The LMP is always the first day of bleeding, not the last. Using the wrong date can shift your due date by 3-7 days and affect the timing of prenatal screenings and milestone tracking.
- Not adjusting for irregular cycles: If your cycle is consistently longer or shorter than 28 days, using the default setting will give an inaccurate due date. A 35-day cycle means ovulation occurs about a week later than assumed, pushing the true due date back by a week.
- Treating the due date as a deadline: Only about 4% of babies arrive on their exact due date. Normal full-term delivery ranges from 37 to 42 weeks. Becoming anxious when you pass the due date is common but usually unnecessary. Discuss post-date management with your provider.
- Ignoring the importance of the dating ultrasound: If your first-trimester ultrasound gives a due date that differs from the LMP-based calculation by more than 5-7 days, the ultrasound date is generally more accurate. Always follow your healthcare provider's recommended due date.
- Comparing your pregnancy timeline to others: Every pregnancy is unique. Symptoms, belly size, weight gain, and timing of fetal movement vary significantly between individuals and between pregnancies. Focus on your own health metrics and your provider's assessments rather than comparing yourself to friends or online experiences.
Frequently Asked Questions
The estimated due date (EDD) is most commonly calculated using Naegele's rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This method was developed by German obstetrician Franz Naegele in the early 19th century and assumes a 28-day menstrual cycle with ovulation occurring on day 14. Our calculator adjusts this calculation based on your actual cycle length. For cycles shorter or longer than 28 days, the formula adds or subtracts the difference from the standard 280 days. For example, a 30-day cycle would add 282 days to LMP. It is important to note that only about 4% of babies are born on their exact due date, and a normal full-term delivery can occur anywhere from 37 to 42 weeks.
Gestational age counts from the first day of the last menstrual period (LMP), which typically precedes conception by about two weeks. This is the standard method used in clinical practice and is what our calculator displays. Fetal age (also called embryonic age or conceptional age) counts from the estimated date of conception, making it approximately two weeks less than gestational age. For example, at 12 weeks gestational age, the fetus is actually about 10 weeks old from conception. Healthcare providers universally use gestational age because the LMP date is usually known with certainty, while the exact date of conception is often uncertain. All pregnancy milestones, screening schedules, and due date calculations reference gestational age.
The first trimester (weeks 1-12) encompasses major organ development. The brain, heart, lungs, and all other vital organs begin forming. By week 8, the embryo is called a fetus. Morning sickness, fatigue, and breast tenderness are common symptoms. The second trimester (weeks 13-27) is often called the most comfortable period. The fetus develops recognizable features, begins moving (quickening usually felt around weeks 16-20), and grows rapidly. Many parents learn the sex during this period. The third trimester (weeks 28-40) involves significant fetal growth and maturation of organs, especially the lungs and brain. The baby gains most of its birth weight during this period. Common maternal symptoms include back pain, difficulty sleeping, and Braxton-Hicks contractions.
A due date calculated from LMP is an estimate, not a guarantee. The accuracy depends largely on how regular your menstrual cycles are and how precisely you remember the date. For those with regular 28-day cycles, LMP-based dating is typically accurate within about 5 days for the first trimester. However, if your cycles are irregular (varying by more than 7 days), ovulation may not follow the assumed day-14 pattern, reducing accuracy. First-trimester ultrasound dating (performed at 7-13 weeks) is considered the gold standard and is accurate to within 3-5 days. If ultrasound dating differs from LMP dating by more than 5-7 days, your healthcare provider will likely adjust the due date to match the ultrasound. Remember that fewer than 5% of babies arrive on their calculated due date.
Yes, and our calculator accounts for this. The average menstrual cycle is 28 days, but normal cycles can range from 21 to 35 days. The key factor is when ovulation occurs, which is typically 14 days before the start of your next period (not 14 days after the start of your last period). For a 35-day cycle, ovulation likely occurs around day 21, meaning conception happens about a week later than the standard model assumes. Our calculator adjusts the due date by adding or subtracting the difference between your cycle length and 28 days. If your cycle is 35 days, 7 days are added to the standard 280, giving you a due date at 287 days from LMP. This adjustment can shift your due date by up to a week or more.
The American College of Obstetricians and Gynecologists (ACOG) defines pregnancy terms as follows: Early term is 37 weeks 0 days through 38 weeks 6 days. Full term is 39 weeks 0 days through 40 weeks 6 days. Late term is 41 weeks 0 days through 41 weeks 6 days. Post-term is 42 weeks 0 days and beyond. Research shows that babies born at 39-40 weeks have the best health outcomes. While babies born at 37-38 weeks are generally healthy, they may have slightly higher rates of breathing difficulties, feeding challenges, and neonatal intensive care admission compared to full-term babies. Healthcare providers generally will not induce labor before 39 weeks without a medical indication. If your pregnancy extends past 41 weeks, your provider will discuss options including induction of labor.
If you are uncertain about your LMP date, there are several ways to estimate your due date. An early ultrasound (ideally between 8-13 weeks) is the most accurate alternative method, measuring the fetus's crown-rump length to estimate gestational age within 3-5 days. If you track ovulation using basal body temperature or ovulation predictor kits, adding 266 days to your estimated ovulation date gives a due date estimate. IVF patients can calculate their due date precisely from the date of embryo transfer. If you have no records at all, fundal height measurement (the distance from the pubic bone to the top of the uterus) can give a rough estimate in the second and third trimesters. Always share your best estimate with your healthcare provider, who can use clinical assessment and imaging to determine the most accurate due date.
Pregnancy dating starts from the last menstrual period (LMP) for practical and historical reasons. The LMP date is usually known with certainty because it is an observable event, while the exact date of conception is typically unknown (sperm can survive up to 5 days in the reproductive tract, making the precise moment of fertilization uncertain). This convention was established long before ultrasound technology existed and remains the international standard because it is reliable, consistent, and allows for universal communication among healthcare providers. Under this system, you are technically considered about 2 weeks pregnant at the time of conception and about 4 weeks pregnant when you miss your first period. While this may seem confusing, it provides a standardized framework that works well for scheduling prenatal care and tracking development milestones.
The standard prenatal care schedule for a low-risk pregnancy includes visits approximately every 4 weeks from weeks 4-28, every 2 weeks from weeks 28-36, and weekly from week 36 until delivery. Key milestone appointments include: first prenatal visit (weeks 8-10) for confirming pregnancy and baseline tests; first-trimester screening and dating ultrasound (weeks 11-13); anatomy scan or mid-pregnancy ultrasound (weeks 18-22); glucose tolerance test for gestational diabetes (weeks 24-28); Group B streptococcus screening (weeks 35-37); and weekly non-stress tests if indicated (weeks 36-40). High-risk pregnancies may require more frequent monitoring. Your healthcare provider will create a personalized schedule based on your health history and pregnancy progression.
The pregnancy progress percentage represents how far along you are in the standard 40-week (280-day) gestation period, adjusted for your cycle length. It is calculated by dividing the number of days since your LMP by the total expected days of pregnancy, then multiplying by 100. For example, at 20 weeks (140 days), you would be 50% through your pregnancy. The progress bar in the calculator uses three colors to represent each trimester: pink for the first trimester (weeks 1-12, about 0-33%), purple for the second trimester (weeks 13-27, about 33-70%), and blue for the third trimester (weeks 28-40, about 70-100%). This visual representation helps you quickly understand where you are in the overall pregnancy timeline and how much time remains until your estimated due date.
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Disclaimer: This calculator is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional for medical guidance.
Last updated: February 23, 2026
Sources
- American College of Obstetricians and Gynecologists (ACOG) — Methods for Estimating the Due Date: acog.org/clinical/clinical-guidance
- World Health Organization — Pregnancy, Childbirth, Postpartum and Newborn Care: who.int/publications
- National Institute of Child Health and Human Development (NICHD) — How Is Due Date Calculated: nichd.nih.gov/health