Due Date Calculator

EDD · LMP · Ultrasound · Conception · IVF · Delivery window

First Day of Last Period ?

Average Cycle Length

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Dates are estimates. Confirm with your clinician. First trimester ultrasound often refines LMP based dates.

👶 Enter LMP, conception, ultrasound, or IVF details to estimate your due date.

Due Date Formulas

An estimated due date (EDD) is a planning midpoint, not a guaranteed birthday. This calculator supports four common clinical dating approaches.

LMP (Naegele style)

EDD = LMP + 280 days + (cycle − 28) Example: LMP Jan 1, 28 day cycle → EDD Oct 8 (280 days later)

Conception date

EDD = Conception + 266 days Example: Conception Mar 15 → EDD Dec 6

Ultrasound gestational age

EDD = Scan date + (280 − gestational days) Example: Scan at 8w0d on Mar 1 → remaining 224 days → EDD Oct 11

IVF transfer

EDD = Transfer + (266 − embryo age days) Day 3 → +263 · Day 5 → +261 · Day 6 → +260

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Professional societies such as ACOG describe how ultrasound and LMP dates should be reconciled when they disagree by more than set day thresholds.

Term Windows & FAQ

Label	Gestational weeks	Meaning
Preterm	Before 37w0d	Born early
Early term	37w0d to 38w6d	Near term
Full term	39w0d to 40w6d	Optimal window for many
Late term	41w0d to 41w6d	Past EDD week
Post term	42w0d and beyond	Often needs close monitoring

How do you calculate a due date?

Add 280 days to the first day of the last menstrual period for a typical 28 day cycle, or use conception, ultrasound, or IVF formulas when those dates are known.

How accurate is a due date calculator?

Few babies arrive on the exact EDD. Most arrive within about a week of it. Early ultrasound can refine uncertain LMP dates.

How is due date calculated from ultrasound?

Convert the reported weeks and days to total gestational days, subtract from 280, and add the remainder to the scan date.

How to Use This Due Date Calculator

Choose LMP, Conception, Ultrasound, or IVF. Enter the matching date fields. Results show the estimated due date, current gestational age, trimester, delivery window markers, and milestone dates.

Use LMP when you know the first day of your last period and your usual cycle length. Use ultrasound when a dating scan reports gestational age. Use conception when ovulation or fertilization timing is known. Use IVF when you have a transfer date and embryo day.

What is an estimated due date?

The EDD is a statistical midpoint around 40 weeks of gestational age. Pregnancy dating usually starts from the last menstrual period even though fertilization happens later. That convention keeps charts and screening windows consistent across clinics.

Only a small percentage of births occur on the exact printed due date. A healthy range often spans early term through late term. Your clinician may discuss induction near or after 41 to 42 weeks depending on your pregnancy.

How to calculate a due date manually

1. Confirm which dating input you trust most. 2. Apply the matching formula above. 3. Count gestational age as days from the implied LMP to today. 4. Mark 37 weeks (early term), 39 weeks (full term), 40 weeks (EDD), and 42 weeks (post term). 5. Treat the result as a plan, then confirm with prenatal care.

Worked LMP example: Last period starts on 1 June 2026 with a 28 day cycle. Add 280 days to reach 8 March 2027 as the EDD. If the cycle averages 35 days, add 7 more days to the EDD because ovulation tends to occur later.

Cycle length adjustments

Naegele style math assumes ovulation near day 14 of a 28 day cycle. Longer cycles usually ovulate later, so the EDD moves later by about (cycle − 28) days. Shorter cycles move the EDD earlier. Irregular cycles make LMP dating less reliable and favor ultrasound confirmation.

Ultrasound redating in practice

First trimester crown rump length dating is typically the most precise ultrasound method. Later scans have wider error ranges. ACOG guidance describes discrepancy thresholds where ultrasound dating should replace LMP dating. This educational calculator shows the ultrasound derived EDD from the gestational age you enter; it does not automatically apply every clinical redating rule.

IVF dating

IVF dating is often more precise because the transfer day is known. Day 5 blastocyst transfers commonly use transfer plus 261 days. Day 3 transfers commonly use plus 263 days. Always follow the due date your fertility clinic documents in the medical record.

Common mistakes

Using the last day of bleeding instead of the first day of the period
Forgetting to adjust for a long or short cycle
Mixing fetal age with gestational age
Treating the EDD as a fixed delivery appointment
Changing dates repeatedly based on late third trimester size alone

Practical scenarios

Someone with regular periods can start with LMP and verify at the first prenatal visit. Someone with uncertain periods or recent hormonal contraception should lean on ultrasound dating. An IVF patient should prefer clinic transfer based dating and still attend recommended scans.

Pair this tool with the Pregnancy Calculator for week by week milestones, or the Pregnancy Weight Gain Calculator for recommended gain ranges by BMI.

Delivery window planning

Think in ranges, not a single day. Early term begins at 37 weeks. Full term covers 39 and 40 weeks for many pregnancies. Late term is 41 weeks. Post term starts at 42 weeks. The calculator marks those dates so leave requests, travel, and childcare plans can target a realistic span around the EDD.

Most people deliver within about one week of the estimated date. That spread is why clinicians avoid treating the printed day as a fixed appointment unless induction or scheduled birth is planned for medical reasons.

When this calculator is useful

Use it to estimate when you are due, how many weeks pregnant you are today, when early term begins, and how far you are from the EDD. It helps plan leave, travel, and prenatal appointments while you wait for clinical confirmation.

When this calculator may not be enough

It cannot diagnose pregnancy, measure the embryo, or replace obstetric judgment about induction, growth restriction, or multiple gestation dating. Twins and higher order pregnancies may follow different clinical pathways.

How to interpret your result

The hero date is your calculated EDD. Gestational age is weeks and days from the implied dating start. The delivery window bar marks where today sits between 37 and 42 weeks. Milestone cards list common prenatal checkpoints relative to your timeline.

Gestational age vs calendar months

People often say pregnancy lasts nine months, while clinics count forty weeks from the LMP. Those frames overlap but are not identical. Trust gestational weeks for screening windows, vaccine timing, and term labels used in prenatal care.

Limitations

Results are informational estimates. Dating assumptions fail when cycles are irregular, LMP memory is uncertain, or scan measurements are entered incorrectly. Confirm every clinical decision with a qualified healthcare professional.

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All dates and values are estimates. Consult your healthcare provider for clinical guidance.

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Methodology notes reference ACOG Committee Opinion on methods for estimating the due date (ultrasound and LMP reconciliation framework).

How do you calculate an IVF due date?

Add 263 days after a day 3 transfer, 261 days after a day 5 transfer, or 260 days after a day 6 transfer, unless your clinic specifies a different documented EDD.

What is the difference between gestational age and fetal age?

Gestational age starts at the LMP. Fetal age starts at conception, about two weeks later in a classic 28 day cycle. Clinics chart pregnancy with gestational age.

Can my due date change?

Yes. Early ultrasound may revise an LMP based EDD when the difference exceeds clinical thresholds. Once a best obstetric estimate is set early, later size based changes are usually avoided without careful review.

When is full term?

Full term is commonly described as 39 weeks 0 days through 40 weeks 6 days. Early term starts at 37 weeks. Late term is 41 weeks. Post term begins at 42 weeks.

Sources & References

American College of Obstetricians and Gynecologists. Committee Opinion: Methods for Estimating the Due Date: acog.org/clinical/.../methods-for-estimating-the-due-date
ACOG news overview of standardized EDD calculation practice: acog.org news release on EDD calculator standards