Pregnancy Due Date Calculator

Estimate your baby's due date from your last period, conception date, or ultrasound.

Pregnancy Due Date Calculator

Estimate your baby's due date and track your pregnancy progress.

Calculation Method

First Day of Last Period

Average Cycle Length: 28 days

21 days45 days

How to Use

Choose your input method

Select LMP, conception date, or ultrasound-based due date calculation.

Enter the relevant date

Input the first day of your last period, conception date, or ultrasound date with gestational age.

Adjust for cycle length if needed

For LMP method, enter your average cycle length if it differs from the standard 28 days.

Review EDD and gestational age

Note your estimated due date, current week of pregnancy, and trimester. Confirm with your healthcare provider.

How is the Due Date Calculated?

The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). Our calculator also adjusts for non-standard cycle lengths and supports conception date and ultrasound-based inputs.

Real-World Examples & Use Cases

First Pregnancy Planning and Calendar Management

For first-time parents, the due date is the anchor for all pregnancy planning: scheduling the first prenatal appointment (typically 8-10 weeks), planning when to announce the pregnancy publicly (often after the first trimester, 12 weeks), mapping out the timing of anatomy scans (18-20 weeks) and glucose tolerance tests (24-28 weeks), arranging maternity or paternity leave, and planning the nursery. Having the EDD early allows parents to synchronize appointments, baby showers, and family preparations with a concrete date on the calendar.

Tracking Gestational Age and Milestones

Pregnancy is divided into three trimesters and 40 weeks of fetal developmental milestones. Knowing your exact gestational age in weeks and days helps parents follow fetal development stages: the heart begins beating around week 6, gender can often be determined by week 14-16, viability outside the womb begins around week 22-24, and the lungs mature significantly around week 34-36. Healthcare providers use gestational age for all clinical decisions — biometric measurements, screening tests, and monitoring growth deviations from expected development curves.

Irregular Cycle Due Date Correction

Naegele's Rule assumes a standard 28-day cycle with ovulation on day 14. Women with irregular cycles or cycles significantly longer or shorter than 28 days will have an inaccurate due date from the standard LMP calculation. A woman with a 35-day cycle typically ovulates on day 21 rather than day 14, shifting the due date 7 days later. This calculator's cycle-length adjustment corrects for this, producing a more accurate estimate before the first ultrasound, which provides the most precise gestational age assessment.

IVF and Assisted Reproduction Due Date Calculation

IVF pregnancies have known fertilization dates (egg retrieval and fertilization date), making traditional LMP-based calculations less applicable. For IVF with a day-3 embryo transfer, the EDD is calculated as fertilization date + 263 days (38 weeks from fertilization, since fertilization is equivalent to day 14 of the menstrual cycle). For day-5 blastocyst transfer, add 261 days. Using the fertilization/transfer date directly produces the most accurate due date for IVF pregnancies, avoiding the uncertainty inherent in estimating from a last period date.

How It Works

Naegele's Rule (LMP method): EDD = LMP + 280 days = LMP + 9 months + 7 days For non-standard cycle lengths: EDD = LMP + 280 days + (Cycle Length − 28 days) Example (standard 28-day cycle): LMP: January 1 → EDD: October 7 (January + 9 months + 7 days) Example (35-day cycle): LMP: January 1 → EDD: October 14 (7 days later than standard) Conception date method: EDD = Conception Date + 266 days (38 weeks from fertilization) Ultrasound method: EDD = Scan Date + (280 − Gestational Age in days at scan) Most accurate when performed before 14 weeks. Trimester boundaries (weeks from LMP): First trimester: weeks 1–13 Second trimester: weeks 14–26 Third trimester: weeks 27–40 Full term: 39 weeks 0 days to 40 weeks 6 days Normal delivery range: 37 weeks to 42 weeks

Frequently Asked Questions

How accurate is the due date calculation?▼

The LMP-based due date is an estimate with approximately 2 weeks of uncertainty in either direction. Only about 5% of babies are born on their exact calculated due date. A first-trimester ultrasound (before 14 weeks) is the most accurate dating method, with a margin of error of approximately ±5-7 days. Second-trimester ultrasounds are less accurate for dating (±2-3 weeks). The ultrasound EDD is given priority over LMP-based calculations in clinical practice when they differ by more than 5-7 days.

What happens if my baby doesn't arrive by the due date?▼

Going past your due date is very common — about 80% of pregnancies deliver within 2 weeks of the EDD. Pregnancy is considered post-term at 42 weeks (2 weeks past the EDD). Between 40 and 42 weeks, healthcare providers typically monitor closely with non-stress tests and biophysical profiles to assess fetal wellbeing. Induction is often recommended at 41-42 weeks to prevent complications associated with very prolonged pregnancy. Every clinical decision about timing is made by your healthcare team based on your specific situation.

When should I have my first prenatal appointment?▼

Most clinicians recommend the first prenatal visit around 8-10 weeks of pregnancy. This timing allows for: early ultrasound confirmation of pregnancy location and fetal heartbeat; accurate gestational age assessment for establishing the EDD; dating of the nuchal translucency screening window (11-13 weeks); blood tests for blood type, rubella immunity, STI screening, and complete blood count. Very early appointments (before 8 weeks) may not show a heartbeat yet on ultrasound, causing unnecessary anxiety. If you have risk factors or fertility treatment history, your provider may schedule earlier.

What is the difference between gestational age and fetal age?▼

Gestational age (GA) is measured from the first day of the last menstrual period — including approximately 2 weeks before conception actually occurs. Fetal age (conceptional age) is measured from the date of actual fertilization (approximately 2 weeks after LMP). A 10-week gestational age pregnancy contains a fetus that is approximately 8 weeks old from fertilization. All standard prenatal tests, growth charts, trimester boundaries, and clinical discussions use gestational age — the LMP-based count. This is why a 40-week pregnancy contains approximately 38 weeks of actual fetal development.

Does the due date change after an ultrasound?▼

Yes — if the first trimester ultrasound measurement (crown-rump length) differs from the LMP-based EDD by more than 5-7 days, clinicians typically adjust the official EDD to the ultrasound-based date. Early ultrasound is more accurate than LMP calculation because it measures actual fetal size. Once established by early ultrasound, the EDD is not changed by later scans (even if growth measurements seem small or large) — later size variations are interpreted as growth concerns rather than dating errors.

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