Enter your last menstrual period date, conception date, or ultrasound measurements to find your estimated due date, current gestational week, trimester, and time remaining. The milestone timeline shows every key development - from the first heartbeat to viability to full term - across all 40 weeks.
🤰 Due Date Calculator
️ Medical Disclaimer: This calculator provides estimates only. Your healthcare provider uses clinical data including ultrasound measurements for accurate dating. Only 5% of babies are born on their exact due date.
Estimated Due Date (EDD)
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40 weeks from LMP
🌱 Trimester Progress
Week 1 - 1st TrimesterWeek 13Week 27Week 40 (EDD)
Pregnancy Milestones
Run the calculator first to see your personalised milestone dates. Past milestones shown in green, current week highlighted.
Run the calculator first.
Week-by-Week Summary
Key developments at each stage. Your current week highlighted.
Week
Baby Size
Key Development
Common Symptoms
How Due Date Is Calculated
Naegele's Rule (LMP Method)
EDD = LMP + 280 days (40 weeks)
More precisely for non-28-day cycles:
EDD = LMP + 280 + (Cycle Length − 28) days
Example: LMP = Jan 1, cycle = 30 days
EDD = Jan 1 + 280 + 2 = Oct 11
Based on the observation that pregnancy lasts
approximately 280 days (40 weeks) from the LMP
for a 28-day cycle.
Conception Date Method
EDD = Conception Date + 266 days (38 weeks)
Conception typically occurs ~14 days after LMP
(at ovulation in a 28-day cycle)
266 days from conception = 280 days from LMP
Both methods give the same EDD for a 28-day cycle.
Ultrasound Dating
EDD = Ultrasound Date + (280 − Gestational Age days)
Gestational Age days = weeks × 7 + extra days
Most accurate in the first trimester (before 13w6d)
Crown-Rump Length (CRL) is measured in 1st trimester
Biparietal Diameter (BPD) used in 2nd trimester
1st trimester ultrasound: accurate to ±5 days
2nd trimester: accurate to ±10-14 days
3rd trimester: accurate to ±3 weeks
IVF Transfer Dating
Day 5 transfer (blastocyst):
EDD = Transfer Date + 261 days
(Because embryo is already 5 days old)
Day 3 transfer (cleavage):
EDD = Transfer Date + 263 days
Day 6 transfer:
EDD = Transfer Date + 260 days
IVF dating is the most precise method since the
exact fertilisation date is known.
Trimesters
First Trimester: Week 1 - Week 12 (Weeks 1–13)
Second Trimester: Week 13 - Week 26 (Weeks 14–27)
Third Trimester: Week 27 - Week 40 (Weeks 28–40+)
Full Term: Week 37 - Week 42
Preterm: Before Week 37
Post-term: After Week 42
Normal delivery window: 38–42 weeks
Frequently Asked Questions
Using LMP (last menstrual period): add 280 days (40 weeks) to the first day of your last period - this is Naegele's rule. Assumes a 28-day cycle with ovulation at day 14. Adjusted for other cycle lengths automatically. Using conception date: add 266 days (38 weeks). Using first-trimester ultrasound: CRL (crown-rump length) measurement gives the most accurate dating before 14 weeks. IVF: add 261 days for a day-5 blastocyst transfer.
LMP method: ±1–2 weeks for regular cycles, less accurate for irregular cycles. First-trimester ultrasound (before 14 weeks): most accurate - within 5–7 days - and is used to confirm or override LMP dating when they differ significantly. Second-trimester ultrasound: ±2–3 weeks. Only about 5% of babies arrive on their exact due date. Most births occur between 38–41 weeks of gestation. The due date is a midpoint estimate, not a precise deadline.
Gestational age (GA) is measured from the first day of the last menstrual period - this is the universal medical standard. Embryonic age counts from actual fertilisation and is 2 weeks less than gestational age. When a doctor says 'you are 10 weeks pregnant,' they mean 10 weeks gestational age - the embryo itself is only 8 weeks old. All standard pregnancy milestones and ultrasound measurements are referenced to gestational age, so always use that term when communicating with your healthcare provider.
This calculator automatically adjusts for your cycle length. Ovulation typically occurs 14 days before the next period, regardless of cycle length. For a 30-day cycle, ovulation is around day 16, so the EDD shifts 2 days later. For a 26-day cycle, ovulation is around day 12, so EDD is 2 days earlier. For very irregular cycles (varying by more than 7–10 days), calendar-based dating is unreliable - first-trimester ultrasound dating is significantly more accurate.
First trimester: Weeks 1–12 (conception through approximately 3 months). Second trimester: Weeks 13–26. Third trimester: Weeks 27 through delivery. These divisions are widely used but not universally standardised - some sources and textbooks define the second trimester as starting at Week 13 or 14, and the third trimester at Week 28. Your obstetrician or midwife may use slightly different cutoffs. The trimester definitions in this calculator follow the most commonly used framework.
Full term is 39–40 weeks 6 days gestational age. ACOG updated terminology: Early term = 37–38 weeks 6 days. Full term = 39–40 weeks 6 days. Late term = 41–41 weeks 6 days. Post-term = 42+ weeks. Babies born before 37 weeks are preterm. Babies born 37–38 weeks are 'early term' - they have better outcomes than preterm babies but may still benefit from additional time in the womb. Most healthy spontaneous labours occur between 38–41 weeks.
Around 24 weeks gestational age, a premature baby has a meaningful chance of survival with intensive neonatal care - this is called the threshold of viability. Approximate survival rates with NICU care: 22 weeks ~10%, 23 weeks ~23%, 24 weeks ~55%, 25 weeks ~76%, 26 weeks ~84%. Every additional week significantly improves outcomes. By 28 weeks, most premature babies do very well. The milestone at 24 weeks is why it is a significant clinical and ethical reference point.
IVF is more precise because the exact fertilisation or transfer date is known. For a day-5 blastocyst transfer: add 261 days to the transfer date (equivalent to LMP minus 14 days, because the blastocyst is already 5 days old at transfer). For a day-3 embryo transfer: add 263 days. IVF pregnancies use the same gestational age scale (40 weeks total from equivalent LMP), but the equivalent LMP is calculated backwards from the known transfer date. Ultrasound at 6–8 weeks confirms the dating.
Pregnancy Due Date Calculator - How EDD Is Calculated and What Each Week Means
Medical note: This calculator provides general educational estimates. Due dates are approximations - only about 5% of babies are born on their exact EDD. Always confirm your due date and gestational age with your obstetrician or midwife, who will use clinical examination and ultrasound findings.
Your estimated due date (EDD) is one of the first pieces of information established in any pregnancy - and it shapes everything from prenatal appointments to maternity leave planning. Understanding how it's calculated, which method is most accurate, and what "40 weeks" actually means helps you contextualise the number your doctor gives you.
Naegele's rule - the LMP method: Add 280 days (40 weeks) to the first day of your last menstrual period. Why 280 days? Because pregnancy is dated from LMP, not conception - conception typically occurs around day 14 of a 28-day cycle, so those 14 extra days are included. The 40-week total includes approximately 2 weeks before fertilisation actually occurred.
Three Ways to Calculate Your Due Date
LMP Method (Most Common)
Add 280 days to the first day of your last period
Assumes 28-day cycle and ovulation at day 14
Adjusted automatically for longer/shorter cycles
Accuracy: ±1–2 weeks for regular cycles
Less reliable for irregular cycles - use ultrasound instead
Foundation of all standard gestational age calculations
Conception & Ultrasound Methods
Conception date: Add 266 days (38 weeks) to the known conception or ovulation date
First-trimester ultrasound (most accurate): CRL (crown-rump length) measurement before 14 weeks - accurate to ±5–7 days
Second-trimester ultrasound: Less precise - ±2–3 weeks by 20 weeks
IVF: Day-5 blastocyst transfer - add 261 days to transfer date
Gestational Age vs Embryonic Age
This distinction confuses many first-time parents. Gestational age - the standard medical measurement - counts from the first day of the last menstrual period, not from conception. Embryonic age counts from actual fertilisation, which is typically 2 weeks later.
When your doctor says "you are 8 weeks pregnant," they mean 8 weeks gestational age. The embryo itself is only about 6 weeks old (embryonic age). This is why the due date calculation adds 280 days from LMP but only 266 days from conception - the 14-day difference represents the time between LMP and fertilisation in a standard cycle.
The Three Trimesters - What Changes in Each
First Trimester (Weeks 1–12): Most critical period of organ formation. All major organs develop. Highest risk of miscarriage (most due to chromosomal abnormalities). Symptoms often most intense: nausea, fatigue, breast tenderness. The nuchal translucency scan and NIPT testing typically happen in Week 10–13.
Second Trimester (Weeks 13–26): Most comfortable for many pregnancies - nausea typically resolves, energy returns. Fetal movement ("quickening") first felt around Weeks 16–20. Anomaly scan (mid-pregnancy ultrasound) at Weeks 18–22. Viability milestone at Week 24.
Third Trimester (Weeks 27–40+): Rapid fetal weight gain. Increased physical discomfort as the uterus expands. Group B Strep test, glucose challenge, and other third-trimester screening. Full term defined as 39–40 weeks; most births occur between 38–42 weeks.
The Delivery Window - When Most Babies Actually Arrive
The 40-week due date is a midpoint estimate, not a deadline. Only about 5% of babies arrive on the exact EDD. The expected delivery window is 37–42 weeks, with most births occurring in the 38–41 week range. The clinical terminology updated by ACOG:
Early term: 37 weeks 0 days to 38 weeks 6 days
Full term: 39 weeks 0 days to 40 weeks 6 days
Late term: 41 weeks 0 days to 41 weeks 6 days
Post-term: 42 weeks and beyond (induction typically discussed)
How this calculator works, and where the numbers come from
The Pregnancy Due Date applies the standard formula for this calculation to the values you enter and updates the result as you type. The calculation itself happens in your browser, and the page explains the method so you can check any result by hand.
Please note: This tool gives general estimates based on published population formulas. It is not medical advice and does not replace assessment by a doctor, dietitian or other qualified professional.