Health & Fitness
Pregnancy Due Date Calculator
Estimate due date, elapsed gestational days, completed weeks, and remaining days from the entered LMP, cycle length, and assessment date. The 40-week timeline marks the LMP anchor, trimester regions, assessment point, and estimated due date.
Estimated due date-
Estimated gestational age-
Estimated days remaining-
Estimated completed weeks-
Decision view
LMP-based 40-week pregnancy timeline
LMP-based 40-week pregnancy timelineThe LMP anchor, trimester regions, assessment date, and estimated due date are positioned on the same calendar timeline.
Exact scenario comparisonUsual cycle length (days) changes while all other entered assumptions remain constant.
| Usual cycle length (days) | Estimated due date | Estimated gestational age | Estimated days remaining | Estimated completed weeks |
|---|
How to use Pregnancy Due Date Calculator
- Enter the first day—not the last day—of the last menstrual period and the usual pre-pregnancy cycle length.
- Enter the assessment date to place the estimate on the gestational timeline.
- Use the result as a calendar reference and follow the dating established by the treating clinician.
Calculator guide
Understanding Pregnancy Due Date Calculator
An LMP-based due date is a calendar estimate anchored to the first day of the last menstrual period and adjusted for the entered cycle length. Clinical dating may change after ultrasound, assisted-reproduction records, or professional assessment.
Calculation method
How the calculation works
Add 280 days to the first day of the last menstrual period and adjust by the difference between entered cycle length and 28 days. Add 280 days to the first day of the last menstrual period, then add the difference between entered cycle length and 28 days. Subtract LMP from the assessment date for elapsed gestational days and subtract assessment date from due date for remaining days.
Dating context
Why a clinician may revise an LMP estimate
Calendar dating is useful, but it depends on assumptions that clinical information can test.
Always use the due date documented by the prenatal care team for clinical decisions.
Worked situations
Practical examples
- For an LMP of June 1, 2026 and a 28-day cycle, the simple estimate adds 280 days.
- A 30-day usual cycle shifts the LMP estimate two days later; a 26-day cycle shifts it two days earlier.
- Completed weeks are elapsed gestational days divided by seven and do not replace a clinician's recorded gestational age.
Better inputs
Useful tips
- Use assisted-conception dates or ultrasound dating when the treating clinician determines they are more appropriate than LMP.
- Record whether cycle length is consistently different from 28 days; irregular cycles weaken calendar assumptions.
- Seek timely prenatal care rather than waiting for an estimated milestone or due date.
Before relying on the result
Limitations and common mistakes
- The method assumes the LMP is known and that cycle-length adjustment reasonably approximates ovulation timing.
- Irregular cycles, recent hormonal contraception, postpartum cycles, bleeding mistaken for menstruation, and uncertain dates reduce reliability.
- A due date is not a prediction of the exact birth date and must not guide urgent symptoms or medical decisions without professional care.
Reference
Key terms
- LMP
- First day of the last menstrual period used as the traditional gestational-age anchor.
- Gestational age
- Pregnancy age conventionally counted from LMP, approximately two weeks before fertilization in a typical cycle.
- Estimated due date
- Calendar reference near 40 gestational weeks, not a guaranteed delivery date.
- Dating ultrasound
- Ultrasound assessment that may establish or revise gestational dating under clinical guidelines.
Important note
Calculated from the entered measurements using the displayed method. It is a general reference and does not replace diagnosis or individualized professional guidance.
Frequently asked questions
Is the due date the day labor will begin?
No. It is a reference date; normal delivery timing varies around it.
Why is pregnancy counted before conception?
Traditional gestational age begins at LMP because the exact date of ovulation and fertilization is often unknown.
What if cycles are irregular?
Calendar dating becomes less reliable. Discuss ultrasound and clinical dating with a prenatal professional.
Can this calculator assess pregnancy health?
No. It provides dates only and cannot assess viability, growth, symptoms, or complications.