PureTools
Due Date Calculator
Find your estimated due date from LMP, conception date, or IVF transfer, with trimester breakdown, current pregnancy week, and 12 key clinical milestones.
Adds 266 days (38 weeks) from conception, the standard gestational period from fertilization to birth.
Day-5 blast: EDD = transfer + 261 days. Day-3 embryo: EDD = transfer + 263 days. Both equal 40 weeks from LMP.
Estimates only, not medical advice. Confirm your due date with your OB or midwife.
Estimated Due Date
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Key Prenatal Milestones
How to use the Due Date Calculator
Choose the input method that matches what you know, your last menstrual period, your confirmed conception or ovulation date, or your IVF transfer date. Enter the date, and the calculator instantly produces your estimated due date (EDD), your current pregnancy week, all three trimester ranges, a progress bar, and 12 key prenatal milestones with their exact projected dates.
- Select a method, LMP is the standard used by most OBs. Conception Date or IVF Transfer give a more personalized result when you know those dates precisely.
- Enter your date, the calculation runs automatically as you type; no button required.
- Review your EDD, the hero card shows your due date and how many weeks remain.
- Check trimester ranges, the three trimester cards show the exact calendar start and end dates for T1, T2, and T3.
- Review key milestones, 12 clinical checkpoints appear with projected dates so you can plan appointments in advance.
- Copy your summary, one button copies all dates in plain text for easy sharing with your provider or partner.
How the due date is calculated
Naegele's Rule, the method used by virtually every OB globally, takes the first day of your last menstrual period and adds 280 days (40 weeks). This assumes ovulation on day 14 of a 28-day cycle. If your cycle is longer or shorter, the calculator adjusts the conception estimate accordingly, though the EDD itself stays at 280 days from the adjusted LMP equivalent. For IVF transfers, the embryo's age at transfer is already known, so the calculation works backward from that: a day-5 blastocyst is treated as 5 days past fertilization, meaning EDD = transfer date + 261 days.
What the milestones mean
The 12 milestones cover the full arc of prenatal care: the early dating ultrasound (8–10 weeks), the critical NT scan (11–14 weeks) that screens for chromosomal conditions like Down syndrome, the anatomy scan (18–20 weeks), the glucose challenge test (24–28 weeks) for gestational diabetes, Group B Strep testing (35–37 weeks), and the weekly provider visits that begin at 36 weeks. All dates are estimates, your actual appointments depend on your provider's protocol and individual risk factors. If you are also tracking your ovulation and fertility cycle, the Ovulation Calculator can help contextualize how your conception timing maps to these milestones.
Frequently asked questions
How is my due date calculated?
The standard method uses Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle and ovulation on day 14. If you know your conception date, the calculator adds 266 days (38 weeks). For IVF, it adds 261 days from a day-5 blastocyst transfer or 263 days from a day-3 embryo transfer. All three methods target the same gestational endpoint: 40 weeks from LMP. Sources: American College of Obstetricians and Gynecologists (ACOG).
How accurate is the estimated due date?
Only about 5% of babies are born on their exact due date. The EDD marks the midpoint of a normal delivery window. Full-term pregnancies range from 39 weeks 0 days to 40 weeks 6 days. Early-term is 37–38 weeks 6 days; late-term is 41–41 weeks 6 days; post-term is 42 weeks or more. Your OB or midwife may revise your EDD after a first-trimester ultrasound, which is the most accurate dating method before 14 weeks. The earlier the ultrasound, the more reliable the dating. Source: ACOG.
What are the three trimesters?
The first trimester spans weeks 1–13 (from LMP through roughly month 3). The second trimester covers weeks 14–27. The third trimester runs from week 28 until birth. Major organ development occurs in the first trimester, making it the most critical period for fetal formation. The second trimester is when most parents feel movement for the first time, called quickening, typically between weeks 16 and 25. The third trimester is dominated by rapid growth, lung maturation, and positioning for delivery.
What prenatal appointments should I expect?
Key milestones include: a dating ultrasound at 8–10 weeks; the nuchal translucency (NT) scan at 11–14 weeks to screen for chromosomal conditions; the anatomy scan (mid-pregnancy ultrasound) at 18–20 weeks; the glucose challenge test at 24–28 weeks to screen for gestational diabetes; Group B Strep (GBS) testing at 35–37 weeks; and weekly visits from 36 weeks onward. Your provider's schedule may vary based on risk factors. All 12 projected milestone dates are shown in the results above. Sources: ACOG, CDC.
What if I have an irregular cycle?
Naegele's Rule assumes a 28-day cycle. If your cycle is shorter or longer, ovulation shifts, and your LMP-based EDD may be off by a few days to a week. The first-trimester ultrasound is more reliable in these cases because it directly measures fetal crown-rump length (CRL) and back-calculates gestational age independent of your cycle. If you know your actual conception or ovulation date, use the Conception Date method on this calculator for a more personalized estimate. The Ovulation Calculator can help you identify your cycle length and ovulation timing if you are still trying to conceive.
When does each trimester start and end in weeks?
Trimester 1: weeks 1–13 (days 1–97 from LMP). Trimester 2: weeks 14–27 (days 98–195). Trimester 3: week 28 to birth (days 196–280+). The transitions happen automatically in this calculator based on your EDD. You will see your current trimester, the exact week and day you are in today, and the projected calendar start dates for each trimester alongside their week ranges.
What is a full-term pregnancy?
Full-term is defined by ACOG as 39 weeks 0 days through 40 weeks 6 days. Early-term is 37–38 weeks 6 days; late-term is 41–41 weeks 6 days; post-term is 42 weeks or more. Babies born before 37 weeks are considered preterm. Organ systems, especially lungs, brain, and liver, continue maturing significantly between weeks 37 and 40, which is why reaching full term matters clinically and why elective deliveries before 39 weeks without medical indication are generally discouraged. Source: ACOG.
Is my pregnancy data saved after I close the tab?
No. All inputs, your LMP date, conception date, or IVF transfer date, are stored only in sessionStorage, which is automatically cleared when you close the tab or browser window. Nothing is ever sent to a server. All calculations run entirely in your browser. Your personal health information remains completely private. This is a core part of PureTools' zero-trace privacy commitment. Your data is never used to train AI models or improve machine learning systems.