CALCULATE WITH CONFIDENCE

Health · Pregnancy, Obstetrics & Breastfeeding

Pregnancy Due Date Calculator

Estimate a due date from the first day of the last menstrual period or a known conception date and optionally calculate gestational age on a chosen date.

Health · Pregnancy, Obstetrics & Breastfeeding

Enter your measurements

Private in-browser calculation · no account or saved health record
Used only for LMP arithmetic.
Leave blank if only the estimated due date is needed.

Health values stay in this browser tab. They are not added to the URL, analytics, storage, or a cloud record.

Health result

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Enter valid values to see the result.

Your entries are calculated in this browser and are not submitted to 365CALCS.COM.

Quick guide

How to use this calculator

  1. Use the labels and unit notes to enter the requested measurement, date, time, or observation exactly as recorded.
  2. Check the visible method, population, and unit basis before using the result; switch modes rather than converting values mentally.
  3. Read the calculation audit and limitations together. The result supports measurement or tracking and does not replace diagnosis, treatment, or urgent medical assessment.

Calculation method

How the pregnancy due date calculator works

LMP estimate = first LMP day + 280 days + (entered cycle length − 28 days); known-conception estimate = conception date + 266 days.

The calculated date is an estimate, not a prediction of the delivery day. A clinician's best obstetric estimate may use early ultrasound, assisted-reproduction dates, and clinical reconciliation.

Worked example

Pregnancy Due Date example

An LMP beginning 1 January with a 28-day cycle gives an estimated due date 280 days later. A chosen reference date can then be expressed as completed weeks plus days.

LMP estimate = first LMP day + 280 days + (entered cycle length − 28 days); known-conception estimate = conception date + 266 days.

Supported inputs

Precision and limits

Supported purpose

Cycle adjustment is transparent arithmetic, not part of ACOG's best-estimate redating rules. Do not use this calculator to replace prenatal care, assess fetal growth, time an urgent symptom, or change an established clinical due date.

Measurement quality

The output is only as reliable as the entered measurement, device, timing, units, and applicable reference population. Recheck unexpected values against the original record.

Clinical boundary

This calculator does not diagnose a condition, choose treatment, change medication, or determine that an urgent symptom is safe to monitor at home. Contact an appropriate health professional or local emergency service when the situation may be urgent.

Privacy

Entered health values and results stay in this browser tab. They are not placed in URLs, analytics, logs, local storage, session replay, or a cloud record by this calculator.

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