Pregnancy Due Date Calculator: LMP, IVF & Ultrasound

Pregnancy Due Date Calculator

Estimate your estimated due date, current gestational age, trimester, and conception window from your last menstrual period, conception date, IVF embryo transfer, or an early ultrasound gestational age.

🎯Common Pregnancy Presets

📝Pregnancy Inputs

Calculation method

Pick the date you know best. Early ultrasound dating is usually the most accurate.

Reference date (LMP, conception, transfer, or scan)

This is the date the selected method is based on.

Average cycle length (days) – LMP only

Standard is 28. Longer cycles push the due date later.

IVF embryo age at transfer

Used only for the IVF transfer method.

Ultrasound gestational age – weeks

Weeks reported at the scan (ultrasound method).

Ultrasound gestational age – extra days

The 0 to 6 extra days beyond the whole weeks.

Today (for gestational age)

Defaults to the current date; change to check any day.

Full-term target for the countdown

Sets the target date used for the days-remaining count.

Estimated due date – 40 weeks gestation

Gestational age today – weeks and days along

Current trimester – based on weeks along

Days remaining – to the target week

🔢Key Pregnancy Numbers

280Days from LMP

266Days from conception

40Weeks gestation

14Days LMP to ovulation

🗓Trimester Timeline

Trimester	Weeks Range	Start Date	End Date	Approx Length
Enter your details above to build the trimester timeline.

📆Weekly Milestone Dates

Gestational Week	Milestone	Calendar Date	Days From Now
Milestone dates appear after you calculate.

⚖Method Comparison For Your Dates

Method	Day Offset	Basis	Estimated Due Date
A side-by-side due date for each method appears here.

🗂Conception To Due Reference

Scenario	Method	Cycle / Embryo	Offset	Gestation	Accuracy Note
Regular cycle	LMP	28-day cycle	+280 d	40 wk 0 d	Good if cycles are regular
Long cycle	LMP	35-day cycle	+287 d	41 wk 0 d	Ovulation shifts later
Short cycle	LMP	24-day cycle	+276 d	39 wk 3 d	Ovulation shifts earlier
Known conception	Conception	Fertilization	+266 d	38 wk 0 d	Best when ovulation is known
Blastocyst	IVF	Day 5 embryo	+261 d	37 wk 2 d	Very precise dating
Cleavage stage	IVF	Day 3 embryo	+263 d	37 wk 4 d	Very precise dating
Early scan	Ultrasound	Crown-rump	Varies	Set at scan	Most accurate in weeks 8 to 13

⚙Naegele's Rule And Method Formulas

Naegele's ruleEstimated due date = first day of LMP + 280 days (40 weeks). Classic form: LMP date, subtract 3 months, add 7 days and one year.

Cycle adjustmentFor an irregular cycle: due date = LMP + 280 + (cycle length – 28) days. A 35-day cycle adds 7 days; a 24-day cycle subtracts 4 days.

Conception methodDue date = conception date + 266 days. Gestational age is measured from LMP, which is about conception date – 14 days.

IVF transferDay-5 transfer: due date = transfer date + 261 days. Day-3 transfer: + 263 days. The embryo age already counts toward the 266 days from fertilization.

Ultrasound ageLMP-equivalent = scan date − (weeks × 7 + days). Due date = LMP-equivalent + 280 days, so the scan re-anchors the whole timeline.

Gestational age todayAge = today − LMP-equivalent, shown as full weeks and remaining days. Trimesters: 1st weeks 1–13, 2nd weeks 14–27, 3rd weeks 28–40.

💡Helpful Due Date Tips

Dating tip: Only about 4 percent of babies arrive on the exact estimated due date. Most healthy births happen anywhere from 37 to 42 weeks, so treat the date as the center of a window rather than a deadline.

Accuracy tip: If your cycle is not 28 days or you are unsure of your LMP, an early ultrasound (weeks 8 to 13) usually gives the most reliable dating, and your provider may update the due date from it.

Note: This pregnancy due date calculator is an estimation and educational tool only. It is not medical advice, diagnosis, or a substitute for prenatal care. Always confirm your due date and any pregnancy decisions with a qualified healthcare provider.

So if you have some other piece of information with which you’re more comfortabley, you can plug it into this calculator and it’ll give you an estimate for when you were due. It’s never quite as easy as having one date on the calendar because pregnancy dating are dependent upon biological assumptions that might not match your own body. This fills in that gap and lets you pick the data point you are most comfortable with.

The first option for most is beginning of their last menstrual period. That’s a date that most women have in mind. Next they add an additional two-hundred and eighty days from that first day of flow. That means you’re supposed to have ovulated on day fourteen, which is assumption built into this traditional method.

Why Your Due Date Is Only an Estimate

If you typically have a long cycle, more than a twenty-eight day period, chances are high that the standard math will puts you early. So the tool allows you to enter in your true average cycle length and not worry if you think you’re overdue when in fact you’re right on schedule. If you tend to bleed every thirty-five days for example, the math adjust your due date accordingly based off late ovulation. It is not much of a tweak but it avoids needless third-trimester anxiety.

But what happens if you’re not counting on your period, because you’re getting fertility treatments? IVF gives you a clear starting point, removing all the uncertainty of following your cycle: We know exactly when the embryo was placed inside your uterus. Was it a day-five blastocyst or a day-three cleavage stage embryo? That make a difference for the math. The calculator will take that into consideration. It accounts for number of days spent in the lab waiting to become part of you, and then adds the rest of pregnancy on top of that. That’s more precise than fudging a fake last period date that muddies up your prenatal screenings and other medical notes.

If you’ve never had regular periods, or you know yours are irregular, then ultrasound dating add yet another level of accuracy. During early ultrasounds (between eight and thirteen weeks), they can uses the baby’s crown-rump length to establish how far along you are. They physically take a measurement which is more reliable than relying on a theoretical timeline based off when you think your last period was. The tool takes your scan measurements, then goes back to try to find equivalent last period date that would produce this particular size. Then it construct the rest of the months accordingly.

Setting the due date manages expectations, so understanding what all of the jargon means can help as well. From that imaginary starting line, the gestational age will be counted forward or at least that’s how it works for doctors. So, technically you’ll be pregnant (and two weeks pregnant!) before you’re even fertile enough to get pregnant. Doctors use same weird medical convention everywhere… And knowing about it allows you to read your own updates with accuracy.

The tool lays out the timeline by milestones and trimesters, indicating exactly when you cross over each phase. Babies is born anywhere from 37-42 weeks. Most full-term births happen anywhere between thirty-seven and forty-two weeks. Your due date isn’t an actual due date; only about four percent of babies arrive on their exact estimated due date. It’s also a midpoint in a range. While it can provide you with an idea of when you’ll give birth, it doesn’t know when labor will strike (otherwise it would of been called “labor”). Treat it as a road map during your pregnancy to help you plot out what happens in those months, but leave room for flexibility.

This is your due date, a guide for your care, not a guarantee of when you will deliver.