How to Predict Your Due Date

How to Predict Your Due Date — LMP, Conception, IVF and Ultrasound Methods Explained

Finding out you’re pregnant is one of the most exciting moments of your life — and the very next question is almost always the same: when is my baby due? Your due date becomes the anchor of your entire pregnancy. Every appointment, every milestone, every trimester transition is measured against it.

The good news is that predicting your due date is straightforward once you understand which method applies to your situation. Whether you know your last period date, your conception date, your IVF transfer date, or have an early ultrasound result — there is a reliable calculation for each one.

This guide walks you through all four methods clearly and simply, so you know exactly how your due date is calculated and what it actually means for your pregnancy journey.

What Is a Due Date and How Accurate Is It?

Your due date — also called the Estimated Due Date or EDD — is the date your baby is expected to be born. It is calculated as 280 days (40 weeks) from the first day of your last menstrual period, which is the global standard used by doctors and midwives.

Here is something important to understand: only about 5% of babies are born exactly on their due date. Most healthy pregnancies deliver somewhere between week 37 and week 42. Your due date is the midpoint of that window — a target, not a deadline.

That said, knowing your due date accurately still matters a great deal. It determines:

• When your trimesters begin and end
• When prenatal tests and scans are scheduled
• When your baby is considered full term
• When your doctor may consider inducing labor if pregnancy goes overdue

The 4 Methods to Predict Your Due Date

Different women have different information available. Here is a clear comparison of all four methods:

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Method 1 — Last Menstrual Period (LMP)

This is the most widely used method and the one most doctors default to at your first prenatal visit.

How it works: Add 280 days to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, the calculation adjusts slightly — our calculator handles this automatically.

Step by step:

1. Note the first day of your last menstrual period
2. Enter your average cycle length — the default is 28 days
3. The calculator adds 280 days and adjusts for your cycle length
4. Your estimated due date and current pregnancy week appear instantly

Example: If your last period started on January 1 with a 28-day cycle, your due date is approximately October 8.

Limitation: This method assumes ovulation happens on day 14 of your cycle. If your cycles are irregular, the result may be less precise.

Method 2 — Conception Date

If you know the approximate date you conceived — perhaps because you were tracking ovulation or used a fertility monitor — this method gives you a reliable due date directly.

How it works: Add 266 days to your conception date. The calculator also works backwards to estimate your LMP by subtracting 14 days from the conception date.

Step by step:

1. Enter the date you believe conception occurred
2. The calculator adds 266 days to find your due date
3. Your trimester and pregnancy progress are shown automatically

Example: If conception occurred on January 15, your due date is approximately October 7.

 

Method 3 — IVF Transfer Date

IVF pregnancies are dated differently because the exact fertilization timeline is known. Instead of estimating from a last period, the calculation starts from the embryo transfer date.

How it works: The due date depends on the age of the embryo at transfer:

• Day 3 embryo — add 263 days to the transfer date
• Day 5 blastocyst — add 261 days to the transfer date
• Day 6 blastocyst — add 260 days to the transfer date

Step by step:

1. Enter your IVF transfer date
2. Select your embryo type — Day 3, Day 5, or Day 6
3. The calculator computes your due date and estimated LMP automatically

Why IVF dating is more precise: Because fertilization happens in a lab under controlled conditions, the exact age of the embryo is known. This removes the uncertainty that comes with estimating ovulation day in natural pregnancies.

Method 4 — Ultrasound Dating

An early ultrasound — ideally performed between 6 and 10 weeks — is the most accurate way to predict your due date. At this stage, all embryos develop at nearly identical rates, so fetal measurements translate directly into a reliable gestational age.

How it works: The sonographer measures the embryo and gives you a gestational age in weeks and days. The calculator subtracts that age from today’s date to find your LMP, then adds 280 days to calculate your due date.

Step by step:

1. Enter the date of your ultrasound scan
2. Enter the gestational age your doctor provided — for example, 8 weeks and 3 days
3. The calculator finds your due date and current pregnancy progress automatically

Why it is the most accurate method: Ultrasound removes the assumptions made by LMP-based calculations — irregular cycles, late ovulation, and cycle length variation all become irrelevant when you have actual fetal measurements.

For more on pregnancy dating standards, visit the American Pregnancy Association for trusted clinical guidance.

Understanding Your Pregnancy Progress

Once you have your due date, our calculator also shows you:

• Current week and day of your pregnancy
• Which trimester you are in right now
• Pregnancy progress bar showing what percentage of your 40-week journey is complete
• Days remaining until your due date
• Trimester timeline with key developments highlighted for your current stage

The three trimesters break down like this:

• First Trimester (Weeks 1–13): Organ formation, heartbeat detectable by week 6, miscarriage risk drops significantly by week 13.
• Second Trimester (Weeks 14–27): Rapid growth, baby movements felt, gender can be determined around week 18, anatomy scan done around week 20.
• Third Trimester (Weeks 28–40+): Baby gains weight rapidly, lungs mature, baby positions for birth. Full term begins at week 37.

Tips for Getting the Most Accurate Due Date

• Use ultrasound if available — a first-trimester scan between 6 and 10 weeks is your most reliable option
• Track your cycle length — even a rough average improves LMP accuracy significantly
• For irregular cycles — skip LMP and use ultrasound or conception date instead
• For IVF pregnancies — always use the IVF transfer method with the correct embryo type
• Don’t stress about the exact date — think of your due date as the center of a 4-week delivery window

Use the Free Due Date Calculator

Rather than calculating by hand, use our free Due Date Calculator. It supports all four methods and instantly shows your due date, current week, trimester, pregnancy progress, and a complete trimester timeline.

Try it here: Due Date Calculator — Predict Your Baby’s Big Day

Frequently Asked Questions

Can my due date change after an ultrasound?
Yes. If your first-trimester ultrasound shows a gestational age that differs by more than 7 days from your LMP-based estimate, your doctor will usually update your due date to match the scan. This is most reliable when done before 14 weeks.

What week is considered full term?
Week 37 is the start of full term. Babies born between weeks 37 and 42 are considered full term. Before week 37 is premature and after week 42 is post-term.

Does cycle length affect my due date?
Yes. The LMP method assumes a 28-day cycle with ovulation on day 14. If your cycle is longer — say 35 days — ovulation happens later, which shifts your due date forward. Our calculator adjusts for cycle length automatically.

How is an IVF due date different?
IVF due dates are calculated from the embryo transfer date rather than the last period. Because the fertilization date is known exactly, IVF dating tends to be more precise than LMP-based calculations for natural pregnancies.

What if I don’t know my last period date?
Use the Conception Date method if you know when you conceived, or use Ultrasound dating if you have early scan results. Both give reliable estimates without needing your LMP.

Conclusion

Predicting your due date doesn’t have to be confusing. The method you use simply depends on what information you already have. LMP works well for regular cycles. Conception date is great if you were tracking ovulation. IVF transfer gives you precise dating from day one. And an early ultrasound is the gold standard when accuracy matters most.

Whatever method fits your situation, knowing your due date early helps you prepare, plan, and make the most of every week of your pregnancy.

Use our free Due Date Calculator to get your estimated due date, trimester, and pregnancy progress in seconds.