DUE DATE TOOL

Pregnancy Countdown

Enter your last period or due date to see exactly where you are — and when to expect your little one.

Your pregnancy due date — also called the EDD — is figured out by adding 280 days to the first day of your last period, using a formula called Naegele's rule. Enter your LMP or known due date below to see how far along you are, what week and trimester you're in, how many days are left, and a live countdown — calculated right in your browser, no data sent anywhere.

days  (22–44, default 28)

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Est. Conception Date
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What Happens in Each Trimester?

Trimester 1
Weeks 1 – 13
💓
First Heartbeat
~Week 6
🔬
First Ultrasound
~Week 8
✅
End of First Trimester
Week 12
Trimester 2
Weeks 14 – 27
👶
Gender Reveal Possible
~Weeks 18 – 20
🦶
Baby Kicks
~Week 20
⭐
Viability Milestone
~Week 24
Trimester 3
Weeks 28 – 40
🎉
Baby Shower Window
~Weeks 28 – 34
🏥
Early Term
~Week 37
🎂
Due Date
~Week 40

How Is a Pregnancy Due Date Calculated?

The most common method is Naegele's rule: take the first day of your LMP and add 280 days. German obstetrician Franz Naegele published this formula in 1812, and it's still the starting point used by OB-GYNs and midwives today. It assumes a 28-day cycle with ovulation around day 14 — which isn't true for everyone, which is why this calculator lets you adjust for your actual cycle length. For IVF pregnancies, the math is different: providers use the embryo transfer date instead of the LMP, since the fertilization date is known exactly.

That said, Naegele's rule is an estimate, not a guarantee. A 2013 study in Human Reproduction (Jukic et al.) found that the median pregnancy from ovulation to birth is 268 days, with a standard deviation of about 10 days from ovulation, and about 14 days when measured from the LMP. Put another way: even in a perfectly healthy pregnancy, the range of normal delivery dates spans roughly five weeks. Only about 4–5% of babies actually arrive on the due date. It's a target, not a deadline.

What pushes that date earlier or later? Cycle length is a big one — longer cycles mean later ovulation, which shifts everything back. Maternal age matters too; women over 35 having their first baby tend to go a little longer. An early ultrasound at 8–13 weeks can tighten the estimate considerably, to within about 5–7 days, by measuring the embryo's CRL. If the ultrasound date and the LMP date disagree by more than 7 days, ACOG guidelines say to go with the ultrasound.

How Far Along Am I? Using This Calculator

Three steps: pick your input mode, enter a date, hit Calculate. If you know your LMP, use that tab. If your OB-GYN already gave you an EDD, use the due date tab. If you tracked ovulation and know roughly when you conceived, the conception date tab will work too.

One thing worth knowing: gestational age is counted from your LMP, not from when conception actually happened. That means you're technically "two weeks pregnant" before you've even conceived. It sounds weird, but it's the standard — providers use it because the LMP is a date you can know, while the exact day sperm met egg usually isn't.

Key Pregnancy Dating Terms

EDD (Estimated Due Date)
The predicted date of childbirth, calculated as 280 days (40 weeks) from the first day of the last menstrual period. Also called the estimated date of delivery.
Gestational Age
The age of a pregnancy counted in weeks from the first day of the last menstrual period — not from conception. A pregnancy at 10 weeks gestational age is 8 weeks post-conception.
LMP (Last Menstrual Period)
The first day of the last normal menstrual period before pregnancy. This date is the standard starting point for all gestational age and due date calculations using Naegele's rule.
Naegele's Rule
The formula OB-GYNs still use today to estimate an EDD from an LMP date. It assumes a 28-day cycle — and if yours isn't, the result needs adjusting. Naegele published it in 1812, which explains both its staying power and its limits.
Crown-Rump Length (CRL)
The measurement from the top of the embryo's head to the bottom of its torso, taken during a first-trimester ultrasound. CRL is the most accurate method for confirming or adjusting gestational age before 14 weeks.

Pregnancy Due Date Questions & Answers

Pretty reasonable for people with regular 28-day cycles, but it does have real limits. Population data shows the average pregnancy runs about 281–282 days from LMP with a standard deviation of 13–14 days — which means the true "expected" window stretches across several weeks on either side of your date. An early first-trimester ultrasound narrows that considerably, which is the stronger method when you can get one.
Per ACOG (last reviewed March 2026): first trimester runs from the LMP through 13 weeks 6 days, the second trimester is 14 weeks through 27 weeks 6 days, and the third trimester is 28 weeks through 40 weeks 6 days. In everyday conversation you'll often hear "weeks 1–12 / 13–26 / 27–40" as a shorthand, but the official clinical boundary has T2 starting at week 14, not week 13.
Ask your provider for a dating ultrasound. Before 14 weeks, measuring the embryo's crown-rump length (how long it is from head to rump) gives a pretty accurate read on gestational age. Once you have an EDD from your doctor, just use the "I know my due date" tab in this calculator and enter that date.
Yes, and it's common. If your first-trimester ultrasound shows the baby measuring more than 7 days off from your LMP estimate, your provider will usually update the date. That's not a problem — it just means the ultrasound gave a better picture than the calendar did. Later ultrasounds are much less reliable for dating because babies grow at different rates after the first trimester, so due date changes in the second or third trimester are rare.
Per ACOG definitions: 37–38 weeks is "early term," 39–40 weeks is "full term," 41 weeks is "late term," and 42+ weeks is "post-term." The 40-week mark is the traditional due date, but babies born anywhere in the 37–42 week window are generally healthy. The terminology changed in 2013 because research showed outcomes aren't equal across that whole range — babies born at 39+ weeks do better on average than those born at 37–38.
About 4–5%. That's it. A 2013 study in Human Reproduction found that natural pregnancy length varies by as much as 37 days between people — even in healthy, uncomplicated pregnancies. Most babies arrive within two weeks of the due date, but treating it as a fixed delivery date is setting yourself up for unnecessary stress. Think of it as the midpoint of a five-week window.
Add 280 days to the first day of your last period. That's Naegele's rule in one sentence. For example, an LMP of January 1 gives you a due date of October 8. This calculator does the math for you automatically — and if your cycles aren't 28 days, you can adjust the cycle length field to get a more accurate estimate.
Yes. Naegele's rule assumes you ovulate on day 14 of a 28-day cycle. If your cycles run longer — say, 35 days — you're probably ovulating around day 21, which pushes your actual due date about a week later than the standard calculation. Shorter cycles shift it earlier. This calculator's cycle length field handles that adjustment automatically.
"Late term" starts at 41 weeks; "post-term" is 42+ weeks. Most providers will start talking about induction somewhere in the 41–42 week range because the risk of complications does go up after that point. In practice, fewer than 5–6% of pregnancies reach 42 weeks — largely because induction is typically offered before then. If you're approaching that window, talk to your OB-GYN rather than going by a calculator.
No. This tool gives you a solid estimate based on Naegele's rule, but it can't factor in your specific cycle history, health conditions, or what an ultrasound might show. Use it to get oriented — but get your actual due date from your doctor or midwife, who can also catch anything worth knowing early.
With IVF, providers skip the LMP entirely and work backward from the embryo transfer date. For a Day 5 transfer, add 261 days. For a Day 3 transfer, add 263 days. It's more precise than LMP dating because you know exactly when fertilization happened. For a rough estimate, enter your egg retrieval date in this calculator's "Conception date" tab.
The short version: when your doctor says you're "10 weeks," they mean 10 weeks from your last period, not from conception. The practical reason this matters is that all prenatal screening windows — first-trimester blood tests, the anatomy scan, the glucose test — are scheduled based on gestational age. If you're thinking in fetal age and your provider is thinking in gestational age, you can miss a window by two full weeks without realizing it. When in doubt, use gestational age for everything clinical.

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About the Author

Cedrick Reese — Founder, DayCountdownCalculator.com

I'm a retired veteran who got into building web tools through affiliate marketing back in the early 2000s — long before anyone was calling it that. After retiring, I picked up a Computer Systems Technician certificate from UEI College and kept building. The pregnancy countdown was one of the most-requested tools from site visitors, so I built it to be genuinely useful: accurate calculations, a real live countdown, and nothing sent to any server. When I'm not coding, I'm either doing traditional woodworking, gardening, or tinkering with something that probably doesn't need tinkering.

Medical Disclaimer
This calculator gives you an estimate — not a clinical diagnosis. Due dates can shift based on ultrasound findings and individual health factors. Your OB-GYN or midwife is the right person to confirm yours and guide your prenatal care.