Calculate conception date, due date, fertility window, and pregnancy timeline with multiple medical dating methods. Get accurate results based on WHO guidelines and obstetric standards.
Your conception date is when pregnancy begins. Calculate it instantly using due date, LMP, or ultrasound dating with medical accuracy based on WHO standards.
Based on your location in the United States, here are relevant healthcare resources:
UK pregnancy care guidelines include:
German pregnancy care guidelines include:
Method: Due Date → Conception Date
Formula: Conception Date = Due Date - 266 days
Medical Basis: Standard obstetric calculation assuming 38 weeks from conception to due date
Save your results or explore more pregnancy tools:
Calculates conception date from estimated due date using standard obstetric formula: Conception = Due Date - 266 days. This method is useful when you have an estimated due date from healthcare providers and want to determine the most likely conception period.
Uses the first day of your last menstrual period to calculate both conception date and due date. Based on Naegele's rule: Due Date = LMP + 280 days. This is the most common method used in early pregnancy before ultrasound dating is available.
Provides the most accurate pregnancy dating, especially in the first trimester. Uses fetal measurements (crown-rump length) to determine gestational age with accuracy within 5-7 days. Recommended by WHO for precise pregnancy dating.
Calculates due date directly from known conception date using the formula: Due Date = Conception + 266 days. This method is useful when you know the exact date of conception and want to determine the expected due date.
Scenario: Due date is March 15, 2025
Calculation: Conception = March 15 - 266 days
Result: Conception around June 22, 2024
Scenario: LMP was January 1, 2025
Calculation: Due date = Jan 1 + 280 days
Result: Due around October 8, 2025
This pregnancy conception calculator provides estimates based on standard obstetric formulas and medical averages. Results are intended for educational and informational purposes only. The actual conception date can vary due to factors like cycle irregularity, ovulation timing, and sperm survival. Always follow the guidance of your healthcare provider for pregnancy dating and management. Ultrasound dating in early pregnancy provides the most accurate estimation. This tool should not replace personalized medical advice from qualified healthcare professionals.
Conception dating is an estimation based on medical averages. The actual conception date can vary due to factors like cycle irregularity, ovulation timing, and sperm survival. Ultrasound dating in early pregnancy (especially first trimester) provides the most accurate estimation, typically within 5-7 days of accuracy according to WHO guidelines.
Gestational age is calculated from the first day of your last menstrual period (LMP), which is typically about 2 weeks before conception occurs. Conception date refers to when the sperm fertilized the egg. This is why a pregnancy is considered 40 weeks from LMP, but only 38 weeks from conception according to standard obstetric calculations.
It's challenging to pinpoint the exact conception date because sperm can survive in the female reproductive tract for up to 5 days, and the exact ovulation time can vary. The calculator provides the most likely date based on your cycle information and medical averages. First-trimester ultrasound provides the most accurate estimation.
Ultrasound dating measures fetal size and development to estimate gestational age. In the first trimester, crown-rump length provides the most accurate dating (±5-7 days). Later ultrasounds may be less accurate for dating as genetic factors influence fetal size more significantly.
If your cycle isn't 28 days, use the advanced options to input your average cycle length. The calculator will adjust the conception date estimation accordingly. Women with longer cycles typically ovulate later, while those with shorter cycles ovulate earlier.
Different dating methods serve different purposes and scenarios: LMP dating is standard for initial estimation, ultrasound provides the most accuracy, due date calculation helps when the due date is known, and conception dating works when the conception date is certain. Healthcare providers often use multiple methods.