Pregnancy Due Date Calculator

Updated Oct 2026 Used 4 times

Use the Pregnancy Due Date Calculator to calculate and interpret estimated due date.

Calculate from

Choose the dating method and date you know.

First day of LMP

Used for LMP dating.

Known conception date

Used when conception is known clinically.

Ultrasound date

Date of the scan used for dating.

Gestational weeks on scan

Completed gestational weeks recorded at the scan.

Additional gestational days

Additional days after completed weeks.

Embryo transfer date

Use the transfer date recorded by the fertility clinic.

Known due date

Used to reverse-estimate conception.

Typical cycle length

Used only for LMP cycle-length adjustment.

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Your result

Pregnancy Due Date

Enter your values, then calculate to see a verified result.

Inputs usedReview the information used for this result.

Full calculation and sourcesLMP uses 280 days plus cycle adjustment; known conception uses 266 days; ultrasound back-calculates from recorded gestational age; day-3 and day-5 IVF transfers use 263 and 261 days.

Versioned calculationFormula v1.0.1

What this result means

Estimate a due date from LMP, conception, ultrasound dating, a known due date or IVF transfer with ACOG-aligned limitations.

Method used

LMP uses 280 days plus cycle adjustment; known conception uses 266 days; ultrasound back-calculates from recorded gestational age; day-3 and day-5 IVF transfers use 263 and 261 days.

Important limitation

LMP dating assumes recalled dates and a cycle model. First-trimester ultrasound or ART-derived dating may supersede this estimate.

Enter the inputsUse values with the units and definitions shown beside each field.

Apply the methodLMP uses 280 days plus cycle adjustment; known conception uses 266 days; ultrasound back-calculates from recorded gestational age; day-3 and day-5 IVF transfers use 263 and 261 days.

Inspect the bridgeReview the primary result and supporting outputs before using it.

Check limitationsConfirm the assumptions, date, jurisdiction or population match your use case.

Interpretation

First-trimester ultrasound or ART-derived dating may establish the clinical date more accurately than recalled LMP.

LMP uses 280 days plus cycle adjustment; known conception uses 266 days; ultrasound back-calculates from recorded gestational age; day-3 and day-5 IVF transfers use 263 and 261 days.

LMP dating assumes recalled dates and a cycle model. First-trimester ultrasound or ART-derived dating may supersede this estimate.

Use this result

Conception Date CalculatorEstimate the reverse date and possible intercourse window.Gestational Age CalculatorCalculate pregnancy weeks and days as of a selected date.Pregnancy Weight Gain CalculatorReview the cited singleton total range by prepregnancy BMI.

Pregnancy Due Date Calculator: purpose and method

Calculates estimated due date, estimated conception, possible conception-window start, and possible conception-window end from calculate from, first day of LMP, known conception date, and ultrasound date with visible method, validation, precision, and limitations.

Keep exploring

3 related pages

Method and test recordFormula v1.0.1

Recorded scope: Pregnancy Due Date Calculator formula, input validation, edge behavior and result presentation.
Publisher: CalculatorGeek
Reviewed by: CalculatorGeek Editorial Team
Recorded review date: 2026-11-03
Next source review: 2027-05-03
Definition fixtures: 1 configured scenarios
Published examples: 1 shown below

Recorded method

Saved five-result U.S. English SERP and observed AI Overview reconciliation; three accessible organic pages inspected and two inaccessible results retained as unverified; current ACOG/NHS source review; deterministic fixtures; PHP/JavaScript parity; and responsive preview QA.

These records describe the published model and reference tests. A test-case count is not a certification of every possible input or an independent specialist review. Editorial policy

Known limitations

LMP dating assumes recalled dates and a cycle model. First-trimester ultrasound or ART-derived dating may supersede this estimate.
Changing legal, medical, exam or statistical conventions must be checked at the source.

Method sources

Latest model update

2026-09-21 -

Reference inputs and expected results

Up to 12 examples from the configured definition fixtures are shown. Expected values use the stated output units; invalid inputs are intended to be rejected.

Case	Inputs	Expected result
Primary worked example	Calculate from: lmp; First day of LMP: 2026-06-01; Known conception date: 2026-06-15; Ultrasound date: 2026-08-24; Gestational weeks on scan: 12 value; Additional gestational days: 0 value; Embryo transfer date: 2026-06-18; Known due date: 2027-03-08; Typical cycle length: 28 value	Estimated due date: 20270308; Estimated conception: 20260615 (allowed numeric tolerance: 0.0001)

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On this page

How a pregnancy due date is estimated

A pregnancy due date is an estimate, conventionally 280 days after the first day of the last menstrual period or 266 days after a known conception date. The calculator also supports gestational age recorded at an ultrasound and day-3 or day-5 IVF transfer dates.

Use the clinician-documented estimated due date for prenatal care. A due date is a reference for pregnancy timing, not a prediction of the exact delivery day.

Use the Conception Date Calculator for the reverse estimate or the Gestational Age Calculator for weeks and days as of a selected date.

Due-date formulas by starting method

LMP due date = LMP + 280 days + (cycle length - 28 days)

Known-conception due date = conception date + 266 days

Ultrasound due date = scan date + [280 - gestational-age days]

IVF due date = day-3 transfer + 263 days; day-5 transfer + 261 days

The cycle-length adjustment applies only to LMP mode. ACOG recommends using ART-derived gestational age for pregnancies resulting from assisted reproductive technology and identifies first-trimester ultrasound as the most accurate way to establish or confirm gestational age.

See the IVF due-date and conception-dating guide for the embryo-age convention.

Worked pregnancy due-date example

For an LMP of June 1, 2026 and a 28-day cycle, the model adds 280 days. The estimated due date is March 8, 2027.

The same model reports June 15, 2026 as the center conception estimate and June 10 through June 16 as the possible conception window. Those supporting dates are estimates; they do not replace a documented ultrasound or ART-derived date.

Which due date should guide care?

Use the documented best obstetric estimate. LMP dating depends on recall and an assumed cycle model. ACOG states that first-trimester ultrasound is the most accurate method to establish or confirm gestational age, and ART-derived dating should be used after assisted reproduction.

Once the due date is established, later changes should be handled by the prenatal-care team. The calculator does not predict spontaneous delivery, assess fetal growth or determine whether a pregnancy is preterm or postterm.

Inputs, outputs and result meaning

Inputs

Calculate from: Choose the dating method and date you know. Available choices are Last menstrual period, Known conception date, Ultrasound gestational age, IVF day-3 embryo transfer, IVF day-5 embryo transfer, and Known due date.
First day of LMP: Used for LMP dating. The supported range is 1900-01-01 through 2100-12-31.
Known conception date: Used when conception is known clinically. The supported range is 1900-01-01 through 2100-12-31.
Ultrasound date: Date of the scan used for dating. The supported range is 1900-01-01 through 2100-12-31.
Gestational weeks on scan: Completed gestational weeks recorded at the scan. The supported range is 0 through 42.
Additional gestational days: Additional days after completed weeks. The supported range is 0 through 6.
Embryo transfer date: Use the transfer date recorded by the fertility clinic. The supported range is 1900-01-01 through 2100-12-31.
Known due date: Used to reverse-estimate conception. The supported range is 1900-01-01 through 2100-12-31.
Typical cycle length: Used only for LMP cycle-length adjustment. The supported range is 21 through 45.

Outputs

Estimated due date: This is the primary result. The visible value is displayed without decimal places.
Estimated conception: The visible value is displayed without decimal places.
Possible conception-window start: The visible value is displayed without decimal places.
Possible conception-window end: The visible value is displayed without decimal places.

The calculator applies the documented method after validating and normalizing the inputs. Keep the result label, unit, selected mode, and stated limitations together when sharing the answer.

Pregnancy due-date questions

Is a due date 40 weeks from the last period?

Conventionally, yes: LMP mode starts with 280 days, or 40 weeks, and adjusts for the entered cycle length relative to 28 days.

Does the due date predict the exact delivery day?

No. It is an estimated reference date used to track pregnancy timing; delivery can occur before or after it.

What if ultrasound and LMP dates differ?

Use the due date documented by the prenatal-care team. ACOG provides gestational-age-specific redating guidance and gives the earliest accurate ultrasound an important role.

How is an IVF due date calculated?

The calculator adds 263 days to a day-3 embryo transfer or 261 days to a day-5 transfer. Use the embryo age and transfer date recorded by the fertility clinic.

Sources and evidence limits

Sources and calculation boundaries were checked November 3, 2026. The cited organizations did not review or endorse this CalculatorGeek page. Clinical records and the documented best obstetric estimate control prenatal decisions.