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Pregnancy Due Date Calculator

Updated Sep 2026 Used 1 times
Choose the dating method and date you know.
Used for LMP dating.
Used when conception is known clinically.
Date of the scan used for dating.
Completed gestational weeks recorded at the scan.
Additional days after completed weeks.
Use the transfer date recorded by the fertility clinic.
Used to reverse-estimate conception.
Used only for LMP cycle-length adjustment.

Guest calculations stay on this device. Signed-in results sync privately.

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 v1.0.0

Formula definitionUnit-normalized calculationFormula v1.0.0

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.

Result actions
1
Enter the inputsUse values with the units and definitions shown beside each field.
2
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.
3
Inspect the bridgeReview the primary result and supporting outputs before using it.
4
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

Keep exploring

2 available tools
Conception CalculatorEstimate conception timing from LMP, due date, conception date, ultrasound dating or IVF transfer and show a wider intercourse window without claiming paternity evidence.Gestational Age CalculatorCalculate gestational weeks and days from an LMP or known due date to a selected reference date.
Public verification recordFormula v1.0.0
Review scope
Pregnancy Due Date Calculator Formula, Input Validation, Edge Behavior And Result Presentation.
Review team
CalculatorGeek Expert Review Team
Verified
2026-09-21
Next source review
2027-09-21
Automated fixtures
1 cases

Review method

Package reconciliation, primary-source mapping, competitor feature comparison, deterministic fixtures, PHP/JavaScript parity and responsive preview QA.

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.

Primary sources

Latest update

2026-09-21 ·

On this page

Direct answer

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

Continue with the Conception Calculator when that method matches your next question.

Continue with the Gestational Age Calculator when that method matches your next question.

Formula and methodology

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.

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

Continue with Conception Calculator or Gestational Age Calculator for the next calculation.

Worked example

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

The calculator retains working precision and rounds only the displayed values.

Interpret the result carefully

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

Inputs, boundary behavior and JavaScript/PHP parity are covered by deterministic release tests.

Use the result for the named task only. Do not stretch it into a legal, clinical, safety or causal conclusion the formula does not support.

Inputs, outputs and result meaning

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.

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.

Frequently asked questions

What method does this calculator use?

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.

How should I round the result?

Keep full precision during the calculation and round only the final display unless a governing standard says otherwise.

What is the main limitation?

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

Can I reproduce the answer?

Yes. The formula, inputs, supporting outputs and worked example are displayed on the page.

Sources

Source research refreshed September 21, 2026. No rankings, review credentials or official affiliation are implied.