Pregnancy Conception Calculator
Enter your estimated due date
How Conception Happens
1. Ovulation
An egg is released from the ovary, typically around day 14 of a 28-day cycle.
2. Fertilization Window
The egg can be fertilized for 12-24 hours after ovulation.
3. Sperm Survival
Sperm can survive up to 5 days in the reproductive tract.
4. Conception
Occurs when sperm fertilizes egg, which may be days after intercourse.
Key Dates Explained
Understanding When You Conceived
Many people want to know exactly when conception occurred. This can be for personal curiosity, medical reasons, or to understand pregnancy timing. While the exact moment of conception is rarely known with certainty, this calculator provides a reliable estimate.
Why Conception Date Differs from Intercourse Date
Conception doesn't happen immediately after intercourse. Here's why:
- Sperm can survive in the female reproductive tract for up to 5 days
- The egg is only viable for 12-24 hours after ovulation
- Fertilization must occur during this narrow window
- If you had intercourse 3 days before ovulation, conception still occurs at ovulation
Gestational Age vs. Fetal Age
Gestational Age
- Counted from last menstrual period (LMP)
- Used by doctors and for due dates
- Full-term pregnancy: 40 weeks
- Includes ~2 weeks before conception
Fetal Age (Conceptional Age)
- Counted from actual conception
- Reflects true age of embryo/fetus
- About 38 weeks at full-term
- 2 weeks less than gestational age
Accuracy Considerations
- Ultrasound method: Most accurate, especially early ultrasounds (6-10 weeks)
- Due date method: Good accuracy if due date was ultrasound-confirmed
- Birth date method: Less accurate as babies can be born early or late
- Cycle variation: Not everyone ovulates on day 14; cycles range from 21-35 days
Important Note
This calculator provides estimates based on standard pregnancy calculations. The actual conception date can vary based on individual cycle length, timing of ovulation, and other factors. For legal or medical purposes requiring precise dating, consult with a healthcare provider who can use clinical methods like early ultrasound measurements.
Frequently Asked Questions
When did I conceive based on my due date?
Conception typically occurs about 266 days (38 weeks) before your due date. Since due dates are calculated at 40 weeks from your last menstrual period (LMP), conception usually happens around 2 weeks after your LMP, during ovulation. Subtract 266 days from your due date for an estimated conception date.
Can conception happen on a different day than intercourse?
Yes, conception often occurs days after intercourse. Sperm can survive up to 5 days in the female reproductive tract, waiting for ovulation. If you had intercourse on Monday and ovulated on Thursday, conception would occur on Thursday - not Monday. The conception date is when fertilization happens, not when intercourse occurred.
How accurate is conception date calculation?
Conception date calculations have a margin of error of several days. The most accurate method uses early ultrasound measurements (before 12 weeks). Calculations based on due date or LMP assume a standard 28-day cycle with ovulation on day 14, which doesn't apply to everyone. Consider it an estimate within a 5-7 day range.
Why is my pregnancy dated from my last period instead of conception?
Pregnancy is dated from LMP because it's usually known with certainty, while exact conception date is often uncertain. This 'gestational age' convention means you're already considered 2 weeks pregnant at conception. A 40-week pregnancy is actually only 38 weeks from conception - the first 2 weeks are before the egg was even fertilized.