Welcome to our professional pregnancy due date calculator. This clinically referenced health tool helps you calculate your health metrics and plan your wellness strategy in real time.
Use our free **pregnancy due date calculator** to estimate your due date, trimester breakdown, and key prenatal milestones instantly. Simply enter the first day of your last menstrual period to run the calculation using the same Naegele's rule formula utilized by obstetricians worldwide.
Due Date Calculator
Find out exactly when you\'ll meet your little one based on your Last Menstrual Period (LMP).
Enter your information to see your timeline.
*Only 5% of babies arrive exactly on their due date. This timeline is a clinical estimate based on Naegele's rule.
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What Your Due Date Actually Means
Your due date is an estimated delivery date, not a deadline. It marks 40 weeks from the first day of your last menstrual period. Only about 5% of babies arrive on their exact due date. Understanding how delivery timing distributes helps you plan without anxiety.
| When Baby Arrives | % of Births | Classification | What It Means |
|---|---|---|---|
| Exactly on due date | ~5% | Right on time | Statistically rare, but perfectly normal |
| Within 7 days of due date | ~50% | Normal range | Half of all deliveries land here |
| 37–38 weeks | ~10% | Early term | Nearly ready; slightly higher rate of breathing difficulty vs full term |
| 39–40 weeks | ~57% | Full term | Ideal window per ACOG; organs fully mature |
| 41 weeks | ~6% | Late term | Provider monitors more closely |
| 42+ weeks | ~3% | Post-term | Induction usually recommended |
| Before 37 weeks | ~10% | Preterm | NICU support may be needed depending on gestational age |
Sources: ACOG Committee Opinion 700 (2017) and CDC National Vital Statistics Reports.
Your Pregnancy Week by Week
Pregnancy spans three trimesters covering distinct developmental milestones. Use this table alongside your calculated due date to understand what is happening at each stage and which appointments to prioritise.
| Trimester | Weeks | Key Developments | What to Expect | Key Screening |
|---|---|---|---|---|
| First | 1–12 | Heart beats at ~6 wks; neural tube, major organs, and limbs form | Nausea, fatigue, breast tenderness; miscarriage risk highest, drops sharply after week 12 | Dating ultrasound (8–10 wks); first-trimester genetic screen (10–13 wks) |
| Second | 13–26 | Baby reaches ~14 in and ~2 lbs; movements felt 18–22 wks; hearing develops | Energy returns; nausea resolves for most; back pain may start; anatomy scan due | Anatomy ultrasound (18–22 wks); gestational diabetes screen (24–28 wks) |
| Third | 27–40 | Rapid weight gain; lungs mature last (~36 wks); baby positions head-down | Shortness of breath, heartburn, Braxton Hicks; visits become weekly after 36 wks | Group B Strep test (35–37 wks); non-stress tests if high-risk or post-dates |
Prenatal Appointment Timeline
Prenatal visits follow a standard schedule in low-risk pregnancies. Knowing what happens at each visit helps you prepare the right questions and ensures nothing is missed.
| When | Visit Type | What Happens |
|---|---|---|
| 8–10 weeks | First prenatal visit | Confirm pregnancy; blood type, Rh factor, CBC, STI screening; dating ultrasound; prenatal vitamin guidance |
| 10–13 weeks | First-trimester screening | Optional nuchal translucency ultrasound + cell-free fetal DNA or quad screen for chromosomal conditions |
| ~16 weeks | Mid-trimester check | Blood pressure, weight, fundal height; review screening results; AFP discussion |
| 18–22 weeks | Anatomy ultrasound | Full fetal anatomy survey; checks all major organs and placenta position; optional sex determination |
| 24–28 weeks | Glucose tolerance test | Screen for gestational diabetes; Rh-negative patients receive Rhogam at 28 weeks |
| 28–36 weeks | Every 2–4 weeks | Blood pressure, fundal height, fetal position, kick counts discussion |
| 35–37 weeks | Group B Strep test | Vaginal/rectal swab; positive result requires IV antibiotics during labor |
| 36–40 weeks | Weekly visits | Cervical checks if indicated; fetal position confirmed; birth plan review; induction discussion if approaching 41 weeks |
How This Calculator Works
This calculator uses Naegele's rule, the method endorsed by the American College of Obstetricians and Gynecologists (ACOG) as the standard for LMP-based due date estimation.
Naegele's Rule Formula:
Due Date = First day of last menstrual period + 280 days (40 weeks)
Equivalently: LMP date + 1 year − 3 months + 7 days
Assumes: A 28-day cycle with ovulation on day 14. If your cycle length differs, the estimate adjusts accordingly.
Source: Naegele FC, 1830. Validated in ACOG Committee Opinion 700 (2017).
ACOG considers a first-trimester ultrasound the most accurate dating method, within plus or minus 5–7 days when performed before 14 weeks. If ultrasound dating differs from LMP dating by more than 7 days in the first trimester, ACOG recommends revising the due date to the ultrasound estimate.
Why Your Due Date Is an Estimate
Naegele's rule assumes a 28-day cycle and ovulation on day 14, which is not true for everyone. Several factors affect how accurate the estimate will be:
- Irregular cycle length: If your cycles are shorter or longer than 28 days, or vary month to month, LMP-based dating is less reliable. An early ultrasound gives a more accurate date.
- Uncertain LMP date: If you are unsure of the first day of your last period, an early ultrasound is the preferred dating method.
- IVF pregnancies: Dating is calculated from egg retrieval date, not LMP, giving a precise gestational age. A day-5 embryo transfer adds 261 days; a day-3 transfer adds 263 days.
- Natural variation in pregnancy length: Research in Human Reproduction (Jukic et al., 2013) found that natural variation in pregnancy length can span up to 5 weeks between women, independent of cycle regularity.
- First vs. subsequent pregnancies: First-time mothers statistically deliver about 8 days later than the estimated due date on average. Subsequent pregnancies are often closer to the estimate.
6 Health Numbers to Track During Pregnancy
Your due date is one number. These six tools help you monitor the metrics that matter most for a healthy pregnancy and postpartum recovery.
Ovulation & Fertility
Identify your fertile window and predict ovulation to plan conception precisely.
Blood Pressure
Preeclampsia affects 5–8% of pregnancies. Track your BP against normal ranges by trimester.
Blood Sugar
Gestational diabetes affects ~10% of pregnancies. Know your numbers before your 24–28 week glucose test.
Daily Hydration
Fluid needs increase during pregnancy. Calculate your personal daily target with electrolyte balance.
Sleep Debt
Sleep disruption peaks in the third trimester. Measure how much rest you are missing and plan recovery.
Mental Health Support
Prenatal and postpartum anxiety affect 1 in 5 women. Screen your mental health support needs.
When to Call Your Provider Immediately
These symptoms require prompt medical evaluation at any point during pregnancy. Do not wait for a scheduled appointment.
- Vaginal bleeding beyond light spotting, especially in the second or third trimester
- Severe or persistent abdominal pain or cramping
- Decreased or absent fetal movement after 28 weeks (fewer than 10 movements in 2 hours)
- Signs of preterm labor before 37 weeks: regular contractions, pelvic pressure, lower back pain, watery discharge
- Severe headache, vision changes, or sudden facial/hand/foot swelling (potential preeclampsia signs)
- Fever above 100.4°F (38°C)
- Painful or burning urination (untreated UTIs can trigger preterm labor)
- Sudden significant weight gain of 4–5 lbs in one week after 20 weeks
Frequently Asked Questions
How do I calculate my due date from my last period?
Add 280 days (40 weeks) to the first day of your last menstrual period. This is Naegele's rule, the standard formula used by obstetricians worldwide. Our calculator does this automatically and adjusts if your cycle length differs from 28 days.
How accurate is a pregnancy due date calculator?
Only about 5% of babies are born on their exact calculated due date. Around 80% of deliveries happen between 37 and 42 weeks. A first-trimester ultrasound before 14 weeks is more accurate than LMP calculation alone, with a margin of plus or minus 5 to 7 days. ACOG recommends revising the due date if ultrasound dating differs by more than 7 days in the first trimester.
Can my due date change after an ultrasound?
Yes. If your first-trimester ultrasound (before 14 weeks) gives a date more than 7 days different from your LMP-based estimate, your provider will typically revise your due date to the ultrasound date. After the first trimester, ultrasound dating becomes less precise, so the original due date is usually kept.
What if my periods are irregular?
If your cycles vary significantly, LMP-based dating is less reliable. An early ultrasound is the preferred method for establishing your due date in that case. You can still use this calculator for an initial estimate, but confirm with your provider using an ultrasound.
What is the difference between gestational age and fetal age?
Gestational age counts from the first day of your last menstrual period, which is about 2 weeks before conception. Fetal age counts from actual conception. All clinical calculations, including this calculator, use gestational age. At 6 weeks pregnant by clinical dating, the embryo is only about 4 weeks old in terms of fetal age.
Is 37 weeks considered full term?
No longer. ACOG updated terminology in 2013. Early term is 37 to 38 weeks and 6 days. Full term is 39 weeks to 40 weeks and 6 days. Late term is 41 weeks, and post-term is 42 weeks or beyond. Babies born at 37 to 38 weeks, while usually healthy, can have slightly higher rates of breathing difficulties compared to full-term babies.
What happens if I go past my due date?
Around 6% of pregnancies reach 41 weeks and about 3% reach 42 weeks. Between 41 and 42 weeks your provider will typically monitor more closely with non-stress tests. ACOG recommends discussing induction starting at 41 weeks and typically recommends it by 42 weeks because complication risk begins to rise after that point.
Does the method of conception (IVF) change how due date is calculated?
Yes. For IVF pregnancies the due date is calculated from egg retrieval date, not LMP. For a day-5 embryo transfer, the due date is 261 days after retrieval. For a day-3 transfer, it is 263 days after retrieval. This makes IVF due dates more precise than LMP-based estimates for natural conception.
Sources
- American College of Obstetricians and Gynecologists: Committee Opinion 700 — Methods for Estimating the Due Date
- ACOG: How Your Fetus Grows During Pregnancy
- CDC National Vital Statistics Reports: Births — Final Data
- Jukic AM et al. (2013): Length of human pregnancy and contributors to its natural variation, Human Reproduction
- Mayo Clinic: Prenatal Care: First Trimester Visits
- Office on Women's Health, U.S. DHHS: Pregnancy
Clinical Focus Areas & Key Concepts Covered: This tool utilizes data relating to due date estimator, integrates pregnancy week by week tracker, and offers guidance on conception date calculator to support your wellness journey.
Medical Disclaimer: This calculator is for general educational purposes only and does not constitute medical advice or professional diagnosis. Always consult a qualified physician or healthcare specialist for clinical guidelines. See our full Medical Disclaimer and Editorial Policy.
Clinical Focus Areas & Key Concepts Covered: pregnancy due date calculator, calculate due date, pregnancy weeks tracker, conception date estimator.
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