Calculate your estimated delivery date using various medical methods including LMP, ultrasound, and IVF.
Only about 4% of babies are born on their exact due date. Most arrive within a window of 2 weeks before or after.
A pregnancy due date calculator answers the most exciting question for any expectant parent: “When will I meet my baby – and how far along am I right now, week by week?”
Your estimated due date (EDD) is approximately 280 days (40 weeks) from the first day of your last menstrual period (LMP) — assuming a regular 28‑day cycle and conception around day 14. Only about 1 in 25 women deliver exactly on their due date; most give birth in the two weeks before or after. So think of the due date as a target, not a deadline.
A good pregnancy calculator has two main modes:
But here’s what most people miss: pregnancy is counted from your LMP, not from conception. At the moment of conception, you’re already considered 2 weeks pregnant. That’s why a due date calculator asks for your LMP – it’s the most practical universal starting point for everyone.
Only about 5% of babies are born on their exact due date. Your healthcare provider will use the due date to schedule tests, monitor growth, and determine whether labor is starting too early or too late. It’s a guide, not a guarantee.
The most common method for estimating a due date is Naegele’s Rule, named after the German obstetrician Franz Karl Naegele. The calculation is surprisingly simple:
Start with the first day of your last menstrual period (LMP)
Add 7 days
Subtract 3 months
Add 1 year (if needed)
LMP was June 1, 2024.
• June 1 + 7 days = June 8, 2024
• June 8 – 3 months = March 8, 2024
• March 8 + 1 year = March 8, 2025 (Estimated due date)
If your cycles are longer or shorter, the due date may need to be adjusted. Some calculators let you input your average cycle length and automatically shift the due date.
If you know the exact date of conception (e.g., tracking ovulation, IUI, or IVF), you can calculate your due date more precisely:
Why 266 days? Pregnancy is actually about 266 days from fertilization to delivery. The LMP method adds an extra 14 days to reach 280 days.
For IVF pregnancies: If you know your embryo transfer date, your due date is calculated based on the age of the embryo at transfer.
If you have irregular cycles or your LMP-based due date seems off, your provider will use an ultrasound to adjust your due date.
Once you know your due date, you can track your progress through key milestones. Here’s what happens – and when you can expect it.
| Milestone | Timing (weeks) | What Happens |
|---|---|---|
| Positive pregnancy test | 4–5 weeks | hCG hormone detectable in urine or blood |
| First prenatal visit | 8–12 weeks | Confirm pregnancy, run initial blood work |
| Dating ultrasound | 6–9 weeks | Confirm intrauterine pregnancy, detect heartbeat, set due date |
| Nuchal translucency (NT) scan | 11–14 weeks | Screen for chromosomal conditions |
| Quickening | 16–25 weeks | First fetal movements (flutters, bubbles) |
| Anatomy scan | 18–22 weeks | Detailed survey of fetal anatomy |
| Gestational diabetes screening | 24–28 weeks | Glucose challenge test |
| Viability | ~24 weeks | Baby has a chance of survival outside the womb |
| Rhogam (if Rh‑negative) | ~28 weeks | Injection to prevent antibody formation that could affect future pregnancies |
| Tdap vaccine | 27–36 weeks | Protects baby from pertussis |
| Group B strep (GBS) test | 36–37 weeks | Swab to check for bacteria |
| Full term | 39 weeks | Baby is developmentally ready for delivery |
| Late term | 41 weeks | 7 days past the due date; additional monitoring often begins |
| Post term | 42 weeks | Considered overdue; induction is often recommended |
Weeks 1–13
Fertilization, implantation, organogenesis (heart, brain, limbs form). Heartbeat detectable (~6–7 weeks). Risk of miscarriage highest (but drops significantly after 12 weeks).
Visits: Initial (8-12 wks), then every 4 weeks
Weeks 14–27
“Honeymoon period” – energy returns, nausea subsides. Baby grows rapidly, you feel movement (quickening). Anatomy scan at 18–22 weeks.
Visits: Every 4 weeks
Weeks 28–40
Baby gains weight rapidly, positions head‑down (usually by 32–36 weeks). You may feel Braxton Hicks contractions, breathing becomes more difficult as baby pushes up.
Visits: Every 2–3 weeks, then weekly after 36 weeks
Your due date determines the timing of critical prenatal screenings and tests. Here’s a quick guide.
| Test | Timing | What It Screens For |
|---|---|---|
| Dating ultrasound | 6–9 weeks | Confirm pregnancy, detect heartbeat, set due date |
| Carrier screening | Preconception or 1st trimester | Cystic fibrosis, SMA, fragile X (based on history/ethnicity) |
| Nuchal translucency (NT) | 11–14 weeks | Chromosomal conditions (often combined with blood test) |
| Cell‑free DNA (NIPT) | 10 weeks or later | Trisomy 21/18/13, sex chromosome conditions |
| Maternal serum AFP | 16–18 weeks | Neural tube defects (e.g., spina bifida) |
| Anatomy scan | 18–22 weeks | Detailed structural survey (organs, limbs) |
| Gestational diabetes screen | 24–28 weeks | High blood sugar during pregnancy |
| Group B strep (GBS) | 36–37 weeks | Bacteria that can pass to baby during delivery |
ACOG recommends Tdap during each pregnancy, as early as possible in the 27–36 week window. During fall/winter respiratory season, annual influenza and COVID‑19 vaccines are also recommended.
| Factor | How It Affects Due Date |
|---|---|
| Irregular menstrual cycles | Naegele’s Rule assumes a 28‑day cycle; longer/shorter cycles shift ovulation and due date. |
| Uncertain LMP | If you don’t remember your LMP, early ultrasound becomes essential for dating. |
| Conception via ART (IVF/IUI) | Exact dates are known, so due date is calculated precisely (conception + 266 days or transfer‑based). |
| Late ultrasound | Early ultrasounds are accurate; later scans are less accurate for dating and usually won’t change EDD unless discrepancy is large. |
| Multiple pregnancies | Twins are often delivered earlier; your provider will individualize the plan. |
If your average cycle length isn’t 28 days, enter it when possible. If you’re unsure, start with LMP and let your provider refine the EDD after an early ultrasound.
| Mistake | Why It’s Wrong |
|---|---|
| Using the date your period ended | Naegele’s Rule uses the first day of LMP; using end date shifts EDD by ~5–7 days. |
| Ignoring cycle length variations | If cycles are longer (e.g., 35 days), ovulation is later, so EDD should be adjusted. |
| Assuming the due date is exact | Only ~5% deliver on EDD; most arrive between 37 and 42 weeks. |
| Changing EDD based on 2nd‑trimester ultrasound | Early ultrasound is most accurate; later growth scans should not routinely change dating. |
| Forgetting IVF/ART details | IVF due dates depend on transfer date and embryo age, not standard LMP assumptions. |
| Relying only on the calculator | An early ultrasound can confirm or refine dating when cycles are irregular or LMP is uncertain. |
Don’t stress over small differences. Use the calculator to start planning, then let your provider fine‑tune with early ultrasound if needed.
→ Input your LMP (and cycle length if not 28 days). Use your EDD to schedule a first prenatal visit around weeks 8–12.
→ Use the calculator for a rough estimate, but expect your provider to rely on an early ultrasound for the official due date.
→ Use conception/IVF mode with transfer date and embryo age. Confirm the EDD with your fertility clinic.
Are you taking a prenatal vitamin with at least 400 mcg of folic acid? It’s most important in the first trimester.
A pregnancy due date calculator is your roadmap for the next 40 weeks. It tells you when to expect your baby, how far along you are, and when critical tests will occur. But it’s not a crystal ball – only about 5% of babies arrive on their exact due date.
*Sources: American College of Obstetricians & Gynecologists (ACOG), UpToDate, Merck Manual, Cleveland Clinic, UC San Diego Health*
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