OnSumoTools

Pregnancy Due Date Calculator

Estimate due date and current gestational age with a trimester timeline.

Method

Due date

Jun 24, 2027

Due in 32 weeks 0 days.

Current gestational age

8 weeks 0 days

Trimester: 1

Trimester progress

Based on an estimated 40-week pregnancy timeline.

Milestone timeline

  • Heart detectable (week 6)

    Gestational age: 6 weeks 0 days

    Oct 29, 2026

  • First trimester end (week 13)

    Gestational age: 13 weeks 0 days

    Dec 17, 2026

  • Anatomy scan (week 19-20)

    Gestational age: 19 weeks 0 days

    Jan 28, 2027

  • Glucose test (week 24-28)

    Gestational age: 25 weeks 0 days

    Mar 11, 2027

  • Third trimester begins (week 28)

    Gestational age: 28 weeks 0 days

    Apr 01, 2027

  • Term (week 37)

    Gestational age: 37 weeks 0 days

    Jun 03, 2027

  • Estimated due date (week 40)

    Gestational age: 40 weeks 0 days

    Jun 24, 2027

This tool uses standard obstetric formulas. Always confirm your due date with your healthcare provider, often using an ultrasound.

How does the Pregnancy Due Date Calculator work step by step?

The calculator supports three estimation methods. Naegele's Rule (LMP): due date = last menstrual period date + 280 days. If your cycle differs from 28 days, the tool adds (cycle length − 28) days to adjust, because ovulation and conception shift proportionally. Conception date method: adds 266 days (38 weeks) directly to the confirmed or estimated conception date, bypassing the LMP-to-conception lag. Ultrasound method: adds the difference between 280 days and the gestational age recorded at your scan (converted to days) to the scan date, back-calculating the corrected due date from the ultrasound measurement. All three methods then calculate current gestational age in weeks and days and project trimester milestones. Key assumption: Naegele's Rule assumes a 28-day cycle and ovulation on day 14; actual ovulation timing varies. Edge case: the 280-day standard targets a singleton pregnancy; twin and higher-order pregnancies have a median delivery date of 36–37 weeks and 34–35 weeks respectively, so the estimated due date is not clinically applicable without medical guidance.

What does a typical Pregnancy Due Date Calculator result look like?

Example: If your last menstrual period started 8 weeks ago and your cycle length is 28 days, your current gestational age is about 8 weeks and your estimated due date is about 40 weeks from LMP. If you enter a 35-day cycle length, the estimated due date shifts later by about 7 days compared with a 28-day cycle.

Frequently asked questions

  • What is LMP?

    LMP stands for the first day of your last menstrual period. Standard obstetric practice counts gestational age from this date even though conception happens roughly two weeks later. Using LMP as the starting point gives a consistent reference that is easy to recall and aligns with the 40-week pregnancy timeline most providers and pregnancy apps follow.

  • How does cycle length affect the due date?

    Standard gestational calculations assume a 28-day cycle with ovulation on day 14. If your cycle is consistently longer or shorter than 28 days, ovulation and conception likely occurred earlier or later than that assumption. The estimated due date shifts by roughly the same number of days as your cycle differs from 28. Gestational age is still tracked from the adjusted LMP reference date.

  • Should I use conception date or ultrasound?

    A first-trimester ultrasound, typically performed between 8 and 13 weeks, provides the most accurate dating because it measures fetal size directly and is less dependent on cycle regularity. Use LMP or conception date as an initial estimate when a dating scan is not yet available. If your ultrasound and LMP dates differ by more than a week, most providers will use the scan date.

  • How accurate are these estimates?

    Due date calculations are estimates, not precise predictions. Only a small percentage of births occur exactly on the estimated due date. Individual variation in ovulation timing, implantation, and fetal growth means the actual birth can reasonably fall two weeks before or after the estimate. Always confirm your due date with your healthcare provider, especially if cycles are irregular.

  • What if my estimated due date has already passed?

    If the calculated date falls before today, the calculator will flag it as past. A due date passing without delivery, called a post-term pregnancy, is a clinical situation that requires monitoring. Providers typically assess the situation with non-stress tests or biophysical profiles and discuss options with you. Contact your healthcare provider promptly for guidance if this applies to you.

Related tools

Estimate your due date

A due date is a best guess, not an appointment. Only about one in twenty babies arrives on the exact day. Still, it's the date your care team plans around, and it helps you picture the months ahead.

Choose a starting point: the first day of your last period, a conception date, or a due date from an ultrasound. The calculator gives your estimated due date, your gestational age today and a timeline of milestones.

What LMP means

LMP is the first day of your last menstrual period. Pregnancy is dated from that day, even though conception happens about two weeks later. That's why a pregnancy counts as roughly 40 weeks while the baby has been growing for about 38.

The standard method, called Naegele's rule, adds 280 days to LMP. It assumes a 28-day cycle. If yours is longer or shorter, enter your cycle length and the tool adjusts, because ovulation shifts with it.

LMP, conception or ultrasound?

Use what you trust most. If your cycles are regular and you know your LMP, it's a good start. If you know the conception date, say from fertility tracking or IVF, that's very precise. A first-trimester ultrasound measures the baby and is often the most reliable method, especially when cycles are irregular or the LMP is uncertain.

If the ultrasound date and the LMP date differ by more than a week or so, many providers go with the ultrasound.

Milestones

The timeline marks things like the end of the first trimester around week 13, the usual detailed anatomy scan around weeks 18 to 22, and the point of viability. It helps you plan appointments and tests, though your provider decides what's right for you.

If your date has passed

It happens often, especially with a first baby. A pregnancy can safely continue a bit past 40 weeks, but providers monitor closely and talk about options if it goes on. Call your care team if you're past your date or you notice anything that worries you, like reduced movement.

This tool offers estimates and isn't medical advice. Your dates stay in your browser.