Free Due Date Calculator — When Is My Baby Due?

Calculate your estimated due date using your last menstrual period, conception date, or IVF transfer date. Includes current trimester and key milestone dates.

Enter your details

Enter the date that matches your selected method above.

Result
Enter your details on the left, then press Calculate.

What is this calculator for?

You just got a positive pregnancy test. The first question after the second pink line: when. When is the baby due. When do I tell my employer. When do I need to take time off work. The due date calculator answers the most-asked question of early pregnancy using Naegele's Rule — the same formula your OB uses at your first appointment.

Naegele's Rule: estimated due date (EDD) = first day of last menstrual period (LMP) + 280 days (40 weeks). This assumes a 28-day menstrual cycle with ovulation on day 14, conception around day 14, and a 38-week gestation from conception. The rule is the medical standard despite known imperfections — actual cycle lengths vary (21-35 days is normal), ovulation timing varies, and conception-to-birth duration varies. Only about 4-5% of babies are born exactly on the EDD; 50% are born within ±7 days; 95% within ±14 days.

For more precise dating: an ultrasound between weeks 8-13 measures crown-rump length (CRL) and produces an EDD with ±5 days accuracy in the first trimester. After week 14, ultrasound dating becomes progressively less accurate (±2-3 weeks by late pregnancy). For IVF pregnancies, conception date is known exactly — use it as the anchor instead of LMP.

This calculator handles all three input methods (LMP, conception date, or IVF transfer date) and outputs your estimated due date, current pregnancy week, current trimester, and key upcoming milestones (genetic screening, anatomy scan, glucose test, etc.).

How to use this calculator

Pick your calculation method. Last Menstrual Period (LMP) is the most common — your OB will use this method at your first appointment. Conception date is more accurate if you know when conception happened (often via tracking ovulation with apps). IVF transfer date is the most precise — used for assisted reproduction pregnancies.

For LMP method: enter the first day of your last period before conception. If you don't remember exactly, estimate within a few days — first-trimester ultrasound will refine the date at your initial OB appointment.

For conception method: enter your best estimate of the date intercourse resulted in pregnancy. The calculator adds 266 days (38 weeks) to derive due date.

For IVF method: enter the date of embryo transfer and whether it was a Day 3 or Day 5 transfer (most modern transfers are Day 5 blastocyst). The calculator adds the appropriate offset to derive due date. IVF dating is the most precise method available since conception timing is known exactly.

If your cycle length differs from 28 days, the calculator can adjust LMP-based dating accordingly. A 32-day cycle means ovulation around day 18 (not 14), shifting the conception date and due date by 4 days.

Understanding your results

The calculator returns your estimated due date, current pregnancy week, current trimester, and a milestone timeline: when to expect first ultrasound, genetic screening, anatomy scan, glucose tolerance test, and other key OB appointments.

How to read it. EDD of August 22 means: conception around November 29 (38 weeks before), LMP around November 15 (40 weeks before). At any given calendar date you can calculate weeks pregnant. Trimester boundaries: T1 = weeks 1-13, T2 = weeks 14-27, T3 = weeks 28-40+.

The "your baby is the size of X" framing common in pregnancy apps comes from typical fetal length at each week. Week 12: lime. Week 20: banana. Week 28: large eggplant. Week 36: large papaya. The comparisons are roughly accurate for typical fetal growth and provide intuitive sense of development progress.

Key milestones with timing context: First positive pregnancy test typically at 4 weeks (just after missed period). First ultrasound at 6-8 weeks confirms viability. NIPT (cell-free DNA test) at 10+ weeks screens for Down syndrome and other chromosomal conditions. Anatomy ultrasound at 18-22 weeks examines fetal anatomy in detail (gender often confirmed here). Glucose tolerance test at 24-28 weeks screens for gestational diabetes. Tdap vaccine recommended at 27-36 weeks. Group B strep test at 35-37 weeks. Full term: weeks 37-42; induction typically considered at 41 weeks if labor hasn't started.

Edge cases. Pregnancies past 42 weeks (post-term): risk increases significantly; most providers induce labor by week 42 at latest. Pregnancies that deliver before 37 weeks: preterm; before 32 weeks is significantly preterm with higher complications. The full-term band (37-42 weeks) is wide; planning around the EDD specifically is risky for important events (don't plan a wedding for week 40 — baby might come at 38).

A worked example

Priya, 31, was tracking ovulation in her cycle-tracking app. Her LMP was March 15, 2026. She conceived around March 29. She wants to know her due date and when key prenatal appointments will fall.

LMP method: March 15 + 280 days = December 19, 2026. EDD: December 19. Today is May 12, 2026; that's 8 weeks 3 days from LMP. She's in early second month, late first trimester pattern. Trimester 1 ends June 12 (week 13).

Milestone timeline based on EDD:

First OB appointment: 8-10 weeks (May 17-31). Ultrasound to confirm pregnancy, set EDD officially, screen for known issues.

NIPT (optional): May 24+ (10 weeks). Blood test that screens for chromosomal conditions; results in 1-2 weeks.

End of first trimester: June 12 (week 13). Miscarriage risk drops significantly; she'll share news publicly.

Anatomy ultrasound: August 4-25 (weeks 19-22). Detailed fetal anatomy check; can confirm gender.

Glucose tolerance test: September 22 - October 6 (weeks 24-28). Screen for gestational diabetes.

Tdap vaccine: October 13 - November 24 (weeks 27-36). Protects baby in early life through maternal antibodies.

Group B strep test: November 24 - December 8 (weeks 35-37).

Full-term window: November 27 (37 weeks) through December 31 (42 weeks). Baby could arrive any time in this window.

Final planning: Priya plans her maternity leave to start by week 38 (December 4). She tells her employer at the end of T1 (mid-June) and finalizes leave plans in T3. The EDD is December 19, but 75% of babies are born in the 37-41 week window — meaning the actual birth might fall in early December or late December. She doesn't schedule anything she can't move from late November through early January.

Related resources

For tracking weekly fetal development, see Pregnancy Week Calculator. For appropriate weight gain throughout pregnancy, the Pregnancy Weight Calculator. For nutrition during pregnancy with appropriate caloric increases, the Calorie Calculator. The American College of Obstetricians and Gynecologists (ACOG) publishes the authoritative US clinical guidelines on pregnancy dating, prenatal care, and milestone testing.

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Frequently asked questions

How accurate is Naegele's Rule for calculating due dates?

Naegele's Rule (LMP + 280 days) is a solid first estimate, but a first-trimester ultrasound crown-rump length (CRL) measurement at 7–12 weeks is more accurate. Studies show births cluster around 39–41 weeks; the most common birth week is 39–40. First-time mothers tend to go slightly past their due date; second-time mothers tend to deliver a bit earlier. Your OB will use the LMP estimate and first ultrasound together to establish your confirmed EDD.

What if I don't know my last menstrual period?

A first-trimester ultrasound (7–12 weeks) can establish gestational age from the fetal crown-rump length (CRL) with high precision. If ultrasound dating differs from LMP dating by more than 5–7 days in the first trimester, the ultrasound date takes precedence. Second-trimester biometry is less accurate for dating. If you're uncertain about your LMP, use the conception date input if you have a better estimate.

What is 'full term' in pregnancy?

ACOG defines full term as 39 weeks 0 days through 40 weeks 6 days. Before 37 weeks is preterm; 37–38 weeks 6 days is early term; 41+ weeks is late term; 42+ weeks is post-term. Elective deliveries before 39 weeks without medical indication are generally discouraged — babies born at 37–38 weeks have higher rates of respiratory, feeding, and developmental challenges than those born at 39+ weeks.

Is my due date accurate?

Within ±14 days for 95% of pregnancies. Only ~5% of babies are born exactly on the EDD; 50% within ±7 days. The wide variance is normal — gestation length varies by genetics, maternal factors, and chance. First-trimester ultrasound dating is more accurate than LMP-based dating (±5 days vs ±2 weeks); your OB may adjust the EDD slightly after the first ultrasound. For planning purposes, treat the EDD as the center of a multi-week window, not a fixed appointment date.

What if my cycle isn't 28 days?

Naegele's Rule assumes 28-day cycles with ovulation on day 14. If your typical cycle is longer (32-35 days), ovulation happens later (day 18-21), shifting your due date 4-7 days later. If your cycle is shorter (24-26 days), ovulation is earlier, shifting due date earlier. The calculator can adjust for non-28-day cycles. First-trimester ultrasound dating bypasses cycle-length issues by measuring actual fetal size; OBs use ultrasound dating when cycle history is irregular or unknown.

When can I expect the baby to actually be born?

The 'normal range' for full-term birth is 37-42 weeks (5-week window). Within that: ~10% of births are 37-38 weeks (early term), ~80% are 39-41 weeks (full term), ~5% are 42 weeks (late term), ~5% before 37 weeks (preterm). Most providers won't induce labor before 39 weeks for elective reasons (research shows worse outcomes for elective early induction). After 41 weeks, induction is offered or recommended. After 42 weeks, induction is standard practice to reduce stillbirth risk. The most-likely single week of delivery is week 40, with week 39 close behind.

How accurate is IVF date for calculating due date?

Most accurate of any method, by far. For a Day 5 (blastocyst) IVF transfer: due date = transfer date + 261 days. For Day 3 transfer: + 263 days. Because conception timing is exactly known (the embryo was placed on a specific day), the resulting due date has minimal uncertainty from the conception side — only typical gestation variation remains. IVF babies have the same ±2 week birth window as non-IVF babies, but the EDD itself is more precise than LMP-based calculations.

What's the difference between 'due date' and 'estimated due date'?

They mean the same thing in practice. 'EDD' (estimated due date) is the medical term that acknowledges uncertainty; 'due date' is the colloquial version. Both describe the date at 40 weeks LMP — the center of the expected birth window. The 'estimated' qualifier reminds patients that the date is not a fixed appointment. Some OBs and apps use 'estimated date of confinement' or EDC, which is an older synonym. All three terms refer to the same calculation and the same meaning: the center of the expected 5-week birth window.

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