Calculator Suite
Pregnancy Weeks Calculator
Calculate gestational age, due date, and track fetal development milestones
Educational use disclaimer
This calculator is for general educational purposes only and is not a medical diagnosis. Results can be incomplete or misleading for some people, including children, athletes, pregnant people, older adults, or people with medical conditions. Consult a qualified health professional for medical advice.
Pregnancy Details
Choose your calculation method and enter the appropriate date
Common Scenarios
8 Weeks (First Trimester)
Early pregnancy - first prenatal visits
20 Weeks (Halfway)
Midpoint - anatomy scan time
32 Weeks (Third Trimester)
Final trimester - preparation phase
Due Next Month
Baby due next month
Recent Conception
Conception 2 weeks ago
Key Milestones
Week 12: End of 1st Trimester
Lower miscarriage risk
Week 20: Anatomy Scan
Detailed ultrasound
Week 24: Viability
Survival with medical care
Week 28: 3rd Trimester
Final growth phase
Week 37: Full Term
Ready for delivery
Week 40: Due Date
Expected delivery
Medical Disclaimer
This calculator provides estimates based on standard pregnancy calculations. Always consult with your healthcare provider for personalized medical advice, accurate dating via ultrasound, and pregnancy monitoring.
How this calculator works
Method, formula, examples, assumptions, and review notes for this calculator.
How this calculator works
- The calculator estimates pregnancy dating from last menstrual period, conception date, or due date depending on the selected method.
- LMP-based dating uses a 280-day pregnancy convention from the first day of the last menstrual period.
- Gestational age and trimester are derived from the estimated due date and today's date.
Formula
Estimated due date from last menstrual period
Plain text formula: Estimated due date = first day of last menstrual period plus 280 days, or about 40 weeks.
EDD = estimated due date
LMP = first day of the last menstrual period
Worked examples
LMP due date estimate
Inputs
- Last menstrual period: January 1, 2026
Calculation
- Add 280 days to the first day of LMP.
- Estimated due date is October 8, 2026.
This estimate is useful for planning, but clinical dating may change after ultrasound and clinician review.
How to interpret your result
- Pregnancy dates are estimates and should be confirmed by a qualified health professional.
- Ultrasound, cycle regularity, fertility treatment dates, and medical history can affect clinical dating.
Assumptions
- LMP-based estimates assume a typical cycle and standard 40-week dating convention.
- Conception-based estimates assume the entered date is accurate.
- Milestones are general educational ranges.
Limitations
- The calculator cannot confirm pregnancy, fetal health, or gestational age.
- Irregular cycles, unknown LMP, assisted reproduction, or medical complications require clinical assessment.
- The output should not be used to make medical decisions without professional care.
Common mistakes
- Counting pregnancy from conception instead of LMP when comparing with clinical week counts.
- Treating the due date as an exact delivery date.
- Ignoring clinician-updated dating from ultrasound or medical records.
Sources
Disclaimer
Educational use disclaimer
This calculator is for general educational purposes only and is not a medical diagnosis. Results can be incomplete or misleading for some people, including children, athletes, pregnant people, older adults, or people with medical conditions. Consult a qualified health professional for medical advice.