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Due date from LMP or ultrasound

Due Date Calculator

This calculator estimates your baby's delivery date from your last menstrual period (LMP), a known conception date, an ultrasound measurement, or an in vitro fertilization (IVF) transfer. It applies Naegele's rule for LMP (280 days plus a cycle-length adjustment) and shows gestational age, trimester boundaries, and American College of Obstetricians and Gynecologists (ACOG) term-window dates. Treat the result as the midpoint of a 37–42 week range, not a single-day prediction, and confirm dating with your obstetric provider.

By Jeff Beem

Updated

These are educational due-date estimates. Confirm dating with your clinician or an early ultrasound.

01

Inputs

28 d

Offsets from a 28-day default (Naegele-style adjustment).

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02

Timeline

Enter dates to compute an EDD.

How to use this calculator

In 01 Inputs, choose LMP, conception, ultrasound, or IVF transfer and enter the anchor date. For LMP, set cycle length on the slider (21–45 days; Naegele adds 280 days plus cycle − 28). For ultrasound, add gestational age in weeks and days from the report. For IVF, pick 3-day or 5-day embryo stage (+263 or +261 days). 02 Timeline shows EDD, gestational age, trimester, term-window dates (37/39/41 weeks), and days remaining. Folk fruit-size text is not clinical sizing. Educational only; confirm dating with your clinician.

Reading your due date timeline

Pick the dating method in section 01 that matches what you know. Section 02 fills in once you enter an anchor date; match the dropdown to the source your clinic used.

Example: LMP January 1, 2026, 28-day cycle

With Last Menstrual Period (LMP) selected, enter January 1, 2026 as the first day of bleeding and leave the cycle slider at 28 days. Naegele's rule adds 280 days (no cycle adjustment at 28) → EDD October 8, 2026. The term band marks September 17 (37 weeks), October 1 (39 weeks), and October 15 (41 weeks). Trimester boundaries land about April 8 (end of 1st) and July 15 (end of 2nd).

Calculate from dropdown and cycle slider

Section 01 switches among LMP, Conception Date (+266 days), Ultrasound Date (scan date plus remaining days to 280 from LMP convention), and IVF Transfer Date (+261 or +263 days by embryo stage). For LMP, the cycle-length slider adjusts Naegele's rule by (cycle − 28) days.

Timeline panel outputs

Section 02 shows EDD, days remaining, gestational age, trimester number, progress bar to 40 weeks, trimester end dates, and the green term-window row. The folk fruit-size line is illustrative only. Processing stays local in your browser.

Due date calculator: LMP, ultrasound, conception, and IVF

This calculator estimates an EDD from last menstrual period, conception, ultrasound, or IVF transfer using standard dating formulas. It shows gestational age and ACOG term labels. Confirm final dating with your clinician.

What this calculator does

Choose a dating path in section 01: LMP with cycle-length adjustment, known conception date, ultrasound with gestational age at scan, or IVF transfer with 3-day or 5-day embryo stage. Section 02 returns estimated due date (EDD), gestational age in weeks and days, trimester number, early/full/late term calendar dates, trimester boundaries, a progress bar to 40 weeks, and days remaining. It does not diagnose pregnancy or import your chart.

How the math works

LMP (Naegele's rule): EDD = LMP + 280 days + (cycle length − 28).

Conception: EDD = conception date + 266 days (38 weeks from fertilization).

Ultrasound: EDD = scan date + (280 − gestational days at scan).

IVF: EDD = transfer + 261 days (5-day blastocyst) or + 263 days (3-day embryo).

Gestational age in the panel counts from implied LMP (about two weeks before calculated conception). Trimester 1 runs through week 13, trimester 2 through week 27, trimester 3 from week 28 in this model.

Limits of the model

LMP math assumes ovulation near cycle midpoint; irregular cycles or late ovulation can skew the date until an early ultrasound confirms it. First-trimester scans often override LMP when dates disagree by more than about seven days. Folk fruit-size comparisons are not clinical measurements. This tool does not estimate ovulation, fertile windows, or menstrual cycle forecasts, and it does not import chart data from your clinic.

FAQ

How do I get an EDD from my last period?

Choose Last Menstrual Period (LMP) in section 01, enter the first day of bleeding, and set average cycle length on the slider (21–45 days). Section 02 shows the estimated due date. The model adds 280 days plus (cycle length − 28) days (Naegele's rule).

Can my due date change after an ultrasound?

Often yes in early pregnancy. Before 14 weeks, crown-rump length is usually within a few days, so many clinics follow a 7-day rule: if the scan disagrees with LMP dating by more than about a week, the EDD moves to match the scan. Use Ultrasound Date mode here with gestational age from the report.

How is an IVF due date calculated here?

Select IVF Transfer Date, enter the transfer day, and pick 3-day or 5-day embryo stage. This model adds 263 days for 3-day embryos or 261 days for 5-day blastocysts. IVF dating is usually the most precise because fertilization timing is known.

What do the term-window dates in section 02 mean?

They mark calendar dates at 37 weeks (early term, EDD − 21 days), 39 weeks (full term, EDD − 7 days), and 41 weeks (late term, EDD + 7 days) measured from your EDD. American College of Obstetricians and Gynecologists (ACOG) labels; confirm with your clinician.

What is the difference between gestational age and fetal age?

Gestational age in section 02 counts from implied LMP (medical standard). Fetal age counts from conception and runs about 2 weeks younger. This calculator displays gestational age in weeks and days from the model.

What percentage of babies are born on the EDD?

Roughly 4%. The EDD is a statistical midpoint, not a single-day prediction. Plan for a window (often 37–42 weeks), not one calendar day.

Why does the fruit-size label appear?

It is a folk comparison keyed to gestational week in the widget, labeled not clinical sizing. It does not replace ultrasound biometry.

When should I call my clinician instead of relying on this tool?

Seek care for bleeding, decreased fetal movement, ruptured membranes, or regular contractions before 37 weeks. This calculator does not diagnose pregnancy or replace prenatal visits.

Sources & citations

References used for the calculation method and definitions. Links open in a new tab when available.

[1]
ACOG Committee Opinion No. 700: Methods for Estimating the Due Date

American College of Obstetricians and Gynecologists guidance on Naegele's rule, ultrasound dating, and when to revise the estimated due date.

[2]
Naegele's Rule: A Reappraisal

Peer-reviewed analysis of the Naegele's rule (LMP + 280 days) used by clinicians worldwide, including accuracy considerations and cycle-length adjustments.

Fitness Reference Note

Informational Use: These calculations (BMI, Calories, etc.) are based on standard statistical formulas and are intended for general reference and goal-setting purposes only.

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