Conception Calculator
Estimate your conception date and due date from your last menstrual period, due date, or known conception date.
Conception Calculator
Enter the first day of your last menstrual period
About Conception Dating
Conception dating helps estimate when fertilization occurred and predicts your due date. This calculator uses standard obstetric methods including Naegele's Rule, which assumes a 280-day (40-week) pregnancy from the first day of your last menstrual period.
•How Conception Dating Works
- –Naegele's Rule: Due date = LMP + 280 days (40 weeks)
- –Ovulation Timing: Typically occurs 14 days after LMP in a 28-day cycle
- –Conception Window: Usually 11-21 days after LMP (±3 days from ovulation)
- –Gestational Age: Measured from LMP, not actual conception
•Understanding Your Results
- –Conception Date: Most likely day of fertilization (ovulation day)
- –Conception Window: Range of possible conception dates (±7 days typical)
- –Due Date: Estimated delivery date (only 5% deliver exactly on due date)
- –Full Term: 37-42 weeks is considered normal delivery range
•Factors Affecting Accuracy
- –Irregular Cycles: Makes conception dating less precise
- –Cycle Length: Assumes standard 28-day cycle (varies 21-35 days)
- –Ultrasound Dating: More accurate in first trimester (±5-7 days)
- –Individual Variation: Every pregnancy is unique
•Important Notes
- –Medical Confirmation: Always confirm dates with healthcare provider
- –Early Ultrasound: Most accurate dating method (first 12 weeks)
- –Due Date Range: Consider ±2 weeks around estimated due date as normal
- –Not Diagnostic: This tool is for estimation only, not medical advice