Formula
Add 280 days to the first day of the last menstrual period and adjust by the difference between the entered cycle length and 28 days.
US pregnancy reference
US Pregnancy Due Date Calculator
Estimate due date and pregnancy week from the first day of the last menstrual period and cycle length. Clinical dating and ultrasound can change the date.
Estimated due date
Enter values to calculate Calculation basis date: May 17, 2026. LMP plus 280 days, adjusted for cycle length.Calculation Basis and Official Sources
Calculation basis date: May 17, 2026. Uses the common 40-week estimate from the first day of the last menstrual period.
For pregnancy confirmation, bleeding, pain, symptoms, medication or appointment timing, use an obstetric clinician or medical service.
Formula and Interpretation
How to read it
Use it to estimate timing. The official due date in medical care may be revised after ultrasound and clinical review.
This calculator and its examples are for general information and rough estimation only. They are not medical diagnosis, treatment advice, pregnancy care advice, nutrition advice, emergency guidance, legal advice, tax advice, insurance advice or any other professional advice.
Actual health, pregnancy and nutrition decisions can differ because of symptoms, age, pregnancy status, medical history, medication, clinical measurements, ultrasound results and a clinician's judgement. Use a qualified health professional or medical service before acting on the result.
Calcitda does not guarantee accuracy, completeness, currentness or suitability for your situation. To the fullest extent permitted by law, we disclaim liability for losses, damages, claims or decisions arising from use of, or reliance on, this page.
Before You Rely on the Result
Practical examples
Enter the first day of the last period to estimate the due date.
Use a 30-day cycle if cycles are usually longer than 28 days.
Do not use the result for urgent symptoms or medication decisions.
What this includes
- Estimated due date
- Estimated pregnancy week and day
- Days left to the estimated due date
What this does not include
- Ultrasound dating and clinical history
- IVF transfer date, ovulation confirmation and multiple pregnancy
- Diagnosis, emergency guidance and treatment advice
When to check official sources
Use an obstetric clinician or medical service for diagnosis, symptoms, medication, appointment timing or official dating.