Pregnancy · Dating

Pregnancy Due Date Calculator

Five accurate methods — last period, conception date, IVF transfer, ultrasound CRL, or working back from a known due date. Plus current week, trimester, days remaining, and milestones.

Last reviewed 28 May 2026

Calculate based on

Typical: 28. Adjust if yours differs.

Estimated due date

Sunday, 14 March 2027

279 days to go

You are about

0w 1d

pregnant — Trimester 1

Date of conception

Sunday, 21 June 2026

Estimated (~2 weeks after LMP)

Pregnancy progress

0% complete

279 days to your estimated due date · Trimester 1 of 3

What does this mean?
Your estimated due date (EDD) is the calendar date when your pregnancy is expected to reach 40 completed weeks. Only about 5 % of babies are born exactly on their EDD — most arrive within the 2 weeks before or after. By 41-42 weeks, almost all spontaneous deliveries have happened; induction is usually offered if you reach 41-42 weeks without labour. Pregnancy is divided into three trimesters: T1 weeks 1-12, T2 weeks 13-26, T3 weeks 27-40.

Key milestones

Based on your calculated EDD

  1. First prenatal visit (8–10 weeks)

    Week 9

    Sunday, 9 August 2026

  2. End of first trimester

    Week 13

    Sunday, 6 September 2026

  3. Anatomy scan (typically 18–22 weeks)

    Week 20

    Sunday, 25 October 2026

  4. Glucose screening (24–28 weeks)

    Week 26

    Sunday, 6 December 2026

  5. Third trimester begins

    Week 28

    Sunday, 20 December 2026

  6. Group B Strep test (35–37 weeks)

    Week 36

    Sunday, 14 February 2027

  7. Full-term (37 weeks)

    Week 37

    Sunday, 21 February 2027

  8. Estimated due date (40 weeks)

    Week 40

    Sunday, 14 March 2027

Due dates are estimates. Only ~5% of babies are born on their EDD; most arrive within ±2 weeks. A first-trimester dating ultrasound (using CRL) is the most accurate single measurement. Read the medical disclaimer.

When is my baby due? Pick the method you have data for

Use the tab that matches what you know: last period, conception date, IVF transfer, an ultrasound CRL reading from your dating scan, or working backwards from a due date your provider already gave you. The calculator gives you the EDD plus current week, trimester, days remaining, and a milestone calendar.

How is the due date calculated from my last period?

Naegele’s rule (named after Franz Naegele, a 19th-century German obstetrician): EDD = LMP + 280 days. The implicit assumption is a 28-day cycle with ovulation on day 14. Because 280 days is 40 weeks, the standard “40 weeks pregnant” phrasing assumes this rule. The calculator above adjusts the EDD if your cycle is not 28 days — longer cycles push EDD later, shorter cycles pull it earlier.

How accurate is my calculated due date?

Fewer than 5% of babies actually arrive on the EDD. About half arrive within 7 days of EDD; the great majority arrive within 14 days either side. Term pregnancy is anywhere from 37 to 42 weeks — a 5-week range. So treat the due date as a window, not a deadline. The 2013 Jukic study (Human Reproduction) confirmed that natural pregnancy length varies by 5+ weeks even among healthy term pregnancies after excluding obvious confounders.

Which method is most accurate?

First-trimester dating ultrasound (CRL) is the gold standard — accurate to ±5 days when done before 14 weeks. IVF dating is similar accuracy because fertilization is known to the day. LMP dating is less accurate (subject to cycle variability, memory, and breakthrough bleeding mistaken for periods). The order:

  1. First-trimester ultrasound CRL (gold standard).
  2. IVF transfer date.
  3. Known conception date.
  4. LMP + cycle length adjustment.

When do ultrasound and LMP disagree — which wins?

ACOG Committee Opinion 700 sets out the thresholds. Use the ultrasound EDD if it differs from LMP EDD by more than:

  • 5 days if ultrasound was before 9 weeks.
  • 7 days at 9 weeks to 13 weeks 6 days.
  • 7 days at 14 to 15 weeks 6 days.
  • 10 days at 16 to 21 weeks 6 days.
  • 14 days at 22 to 27 weeks 6 days.
  • 21 days at 28 weeks onwards (with caution — later ultrasound dating is less reliable).

How do you work out the due date with IVF?

IVF dating is precise because fertilization happens in the lab on a known date. The formula:

EDD = transfer date + (266 days − embryo age at transfer)

  • Day-3 transfer: add 263 days to transfer date.
  • Day-5 blastocyst transfer: add 261 days.
  • Frozen embryo transfer: same formula, embryo age at thaw.

What does the dating scan actually measure?

The first-trimester dating scan measures crown-rump length (CRL) — from the top of the head to the bottom of the buttocks. Between 6 and 14 weeks, fetal growth is remarkably consistent across pregnancies, making CRL the most accurate single measurement. The Robinson-Fleming 1975 formula is what most ultrasound machines apply:

GA_days = 8.052 × √CRL_mm + 23.73

After 14 weeks, individual variation grows and biparietal diameter (BPD) and femur length (FL) take over for dating.

What does 'term' actually mean?

ACOG breaks term into four parts:

  • Early term: 37 wk 0 d through 38 wk 6 d
  • Full term: 39 wk 0 d through 40 wk 6 d
  • Late term: 41 wk 0 d through 41 wk 6 d
  • Post term: 42 wk 0 d and beyond

Best neonatal outcomes are at full term (39-41 weeks). Most providers don’t intervene actively until late or post-term unless other factors are present.

Different scenarios — how the EDD changes

Scenario 1: Regular 28-day cycle, LMP 1 January

Naegele’s rule: 1 January + 280 days = 8 October.

Scenario 2: 35-day cycle, LMP 1 January

Ovulation day 21 (not day 14), so conception ~1 week later. EDD = 1 January + 280 + 7 = 15 October.

Scenario 3: 25-day cycle, LMP 1 January

Ovulation day 11, conception 3 days earlier. EDD = 1 January + 280 − 3 = 5 October.

Scenario 4: IVF day-5 transfer on 15 February

EDD = 15 February + 261 days = 3 November.

Scenario 5: LMP calculated EDD = 8 October. 12-week dating scan CRL = 60 mm

CRL 60 mm = 8.052 × √60 + 23.73 ≈ 86 days = 12 wk 2 d. If your scan was 2 weeks earlier than that LMP calculation predicted, the scan will set a new EDD — following ACOG’s threshold rules (under 9 weeks ±5 days, 9-14 weeks ±7 days etc.).

What milestones happen at which weeks?

  • Week 5-6: first positive home pregnancy test; nausea may start.
  • Week 8-10: booking appointment with midwife / OB.
  • Week 11-13+6: first-trimester combined screen (nuchal translucency + bloods) or NIPT.
  • Week 12: dating scan in most UK areas (combined with combined screen).
  • Week 16-18: quad screen if NIPT not done.
  • Week 18-22: anomaly / 20-week scan (anatomy).
  • Week 20: halfway! Often baby movements first felt.
  • Week 24: viability milestone (intervention possible if preterm).
  • Week 24-28: GDM screen (OGTT or two-step).
  • Week 28: third trimester starts; anti-D if Rh-neg; kick counting starts.
  • Week 36-37: early term begins; hospital bag ready; carseat installed; birth plan finalised.
  • Week 37: full term begins.
  • Week 40: EDD.
  • Week 40-42: stretch-and-sweeps offered; induction discussed.

What this calculator does NOT do

  • It doesn’t assess fetal growth, amniotic fluid, placenta, or signs of labour.
  • It doesn’t diagnose miscarriage, ectopic, or molar pregnancy.
  • It doesn’t replace your dating scan — the scan trumps the calculator.
  • It assumes a singleton pregnancy — twins / triplets have different actual delivery windows.

Sources

  • ACOG Committee Opinion 700. Methods for Estimating the Due Date. Obstet Gynecol 2017;129:e150-e154.
  • Robinson HP, Fleming JE. A critical evaluation of sonar “crown-rump length” measurements. Br J Obstet Gynaecol 1975;82:702-710.
  • Jukic AM, et al. Length of human pregnancy and contributors to its natural variation. Hum Reprod 2013;28:2848-55.
  • NICE NG201. Antenatal care. 2021.
  • RCOG Green-top Guideline 31. Investigation and management of the small-for-gestational-age fetus.

See our methodology. Not a substitute for medical advice — read the medical disclaimer.

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Frequently asked questions

How is my due date calculated?
The standard method (Naegele's rule) adds 280 days (40 weeks) to the first day of your last period. It assumes a 28-day cycle with ovulation on day 14. If you have a longer or shorter cycle, the due date shifts: a 32-day cycle pushes it 4 days later; a 25-day cycle pulls it 3 days earlier. More accurate methods use a known conception date, IVF transfer date, or an early ultrasound CRL (crown-rump length) measurement. Use whichever input you have.
Which due date method is most accurate?
A first-trimester dating ultrasound that measures CRL is the gold standard — accurate to ±5 days when done before week 14. After 14 weeks, ultrasound dating accuracy drops. ACOG Committee Opinion 700: use ultrasound EDD when it differs from LMP EDD by more than 5 days (<9 weeks), 7 days (9-14 weeks), 10 days (14-16 weeks), 14 days (16-22 weeks), 21 days (22-28 weeks), 28 days (28+ weeks). IVF dating is also very accurate because the fertilization date is known exactly.
Does my cycle length affect my due date?
Yes. Naegele's rule assumes day-14 ovulation. If your cycle is consistently longer (e.g. 35 days), you ovulate later (day ~21), so conception happens later, so your due date is later — by 7 days. The calculator above adjusts automatically when you enter your cycle length. If your cycles are irregular, your early ultrasound will set the more accurate date.
How accurate is the calculated due date?
Fewer than 5% of babies actually arrive on their calculated EDD. About half arrive within 7 days of EDD; the great majority arrive within 14 days either side. Term pregnancy is anywhere from 37 to 42 weeks — a 5-week range. So treat the due date as a WINDOW, not a deadline. The 2013 Jukic study (Human Reproduction) found that natural pregnancy length varies by 5+ weeks even among healthy term pregnancies.
What's the difference between gestational age and fetal age?
Gestational age is counted from the first day of your last period (LMP). When clinicians say 'you're 12 weeks pregnant', they mean gestational age. Fetal age (or conceptional age) is counted from the moment of conception, about 2 weeks LATER than the LMP. So at '12 weeks gestational age', the embryo / fetus is actually about 10 weeks old. Clinicians use gestational age in almost all documentation and ultrasound dating.
What is CRL and how is it used?
CRL = Crown-Rump Length, measured by ultrasound from the top of the fetal head to the bottom of the buttocks. Between 6 and 14 weeks, fetal growth is so consistent across pregnancies that CRL predicts gestational age to ±5 days. After 14 weeks, individual variation grows and biparietal diameter (BPD) and femur length (FL) take over for dating. The standard formula is Robinson-Fleming 1975: GA_days = 8.052 × √CRL_mm + 23.73.
I had IVF — how is my due date worked out?
IVF dating is precise because the fertilization date is known exactly. EDD = transfer date + (266 days − embryo age at transfer). DAY-3 TRANSFER: add 263 days. DAY-5 BLASTOCYST TRANSFER: add 261 days. FROZEN EMBRYO TRANSFER: same formula based on embryo age. Donor egg cycles: use the donor's egg-retrieval date for the same calculation. IVF EDDs are second only to first-trimester ultrasound in accuracy.
What does 'term' actually mean?
ACOG breaks the term window into four parts: EARLY TERM (37 wk 0 d to 38 wk 6 d), FULL TERM (39 wk 0 d to 40 wk 6 d), LATE TERM (41 wk 0 d to 41 wk 6 d), POST TERM (42 wk 0 d onwards). Most providers don't intervene actively until late or post-term unless other factors are present. The optimal outcomes (lowest neonatal complications) are at full term — between 39 and 41 weeks.
When will I have my dating scan?
UK NHS: dating scan offered 8-14 weeks (most commonly 11-13+6 weeks, combined with the nuchal translucency screen). US: dating scan usually at first prenatal visit if there's any uncertainty about LMP, or as part of standard early ultrasound 8-13 weeks. The earlier the scan, the more accurate the dating. If your scan EDD differs significantly from your calculated EDD, the scan EDD becomes your official EDD.
What if I don't remember my last period?
Common — many people don't track LMP especially when not actively trying to conceive. Options: (1) use the conception date if you know it; (2) use the IVF transfer date if applicable; (3) wait for the early ultrasound scan (CRL) which will set the date. Don't worry — your first booking visit will set an accurate EDD. If your cycles are irregular or you've recently come off hormonal contraception, ultrasound dating is more accurate than LMP anyway.
Why might my due date be changed at my scan?
An early ultrasound CRL measurement is more accurate than LMP-based calculation. ACOG Committee Opinion 700 sets out exact thresholds: if CRL EDD differs from LMP EDD by more than 5-7 days in early pregnancy, the scan EDD becomes the official one. This isn't a mistake — it's a more accurate measurement replacing an estimate. Your medical notes will reflect the scan EDD from then on.
Should I plan around the due date or two weeks before?
Reasonable to be prepared from 37 weeks (early term). Hospital bag packed by 36-37 weeks. Carseat installed and tested. Birth plan finalised. Maternity leave timed to start a week or two before EDD if you have flexibility — some women want to be at work right up to the date, others want a buffer. For second + babies, plan earlier — fewer first-time mums deliver early, but second+ mums often deliver on or just before EDD.
What's the difference between LMP date and conception date?
LMP is the first day of your last menstrual period — what gestational age is measured from by convention. Conception is about 2 weeks LATER (around ovulation, typically day 14 of a 28-day cycle). So at any point in pregnancy, gestational age is about 2 weeks higher than the actual embryonic/fetal age. The 280-day (40-week) figure includes those 2 pre-conception weeks.
Can my due date be earlier than expected with twins?
Twin pregnancies have a different normal length: DICHORIONIC TWINS (two placentas) average 37 weeks; MONOCHORIONIC TWINS (sharing one placenta) often delivered at 36-37 weeks; MONOAMNIOTIC TWINS (sharing one sac) usually delivered at 32-34 weeks. The 'due date' calculation still applies (the same 40-week count) but the actual delivery is usually earlier. Triplets / higher: 32-34 weeks average. Your obstetric team will plan around this.
What is post-term pregnancy and what happens?
Pregnancy that has gone past 42 weeks. Becomes uncommon — most women are offered induction between 41+0 and 42+0 weeks because of slightly higher risks beyond 42 weeks (stillbirth, meconium, macrosomia, placental insufficiency). UK NICE: offer induction between 41+0 and 42+0. ACOG: offer between 41+0 and 42+0. Stretch-and-sweeps from 40 weeks can sometimes start labour spontaneously and avoid induction.
What does the calculator give me besides the due date?
It gives you: estimated due date, your current pregnancy week and trimester, days remaining, estimated conception date, and a milestone calendar of common pregnancy stages (12-week scan, 20-week anomaly scan, viability at 24 weeks, full term 37 weeks, etc.). Use the reverse method if you already have a due date from your provider and want to work backwards to conception date or last period.
How does this relate to other calculators on BumpBites?
Companion: /calculators/ovulation for finding conception timing; /calculators/conception-date for the reverse calculation; /calculators/pregnancy-week for the current week and milestone tracker; /calculators/baby-size-by-week for size comparisons; /calculators/due-date-countdown for the countdown widget; /calculators/maternity-leave for leave timing.

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