Enter your due date or recent ultrasound measurements to calculate the exact date of conception.
Estimated Conception Date
Saturday, May 30, 2026
Intercourse between Mon, May 25 – Sat, May 30 most likely resulted in this pregnancy.
Note: Medical conception (fertilization) occurs precisely when the sperm meets the egg, which is typically on the day of ovulation. Because sperm can live inside the body for up to 5 days, intercourse leading to conception may have happened several days prior. This tool provides an estimate for personal reference only — it is not medical advice or proof of paternity. Talk to your healthcare provider for confirmed pregnancy dating.
Last updated: July 2026
Working Backwards to Find Conception
Whether you're curious about your conception date, or you're trying to figure out which cycle led to your pregnancy, the math can be incredibly confusing. Because obstetricians calculate pregnancy weeks starting from your Last Menstrual Period (LMP)—before you were even pregnant—trying to find the actual date of fertilization requires working backward. Our Conception Calculator does this automatically.
The Two Ways to Calculate Conception
Our calculator offers two methods for finding your conception date based on the information you have available.
1. Using Your Estimated Due Date (EDD)
If your doctor has given you an official due date, finding your conception date is simple. Human gestation lasts an average of 280 days from the LMP, but only 266 days from conception. We simply subtract exactly 266 days from your due date to pinpoint the day the egg was likely fertilized.
2. Using an Ultrasound Date
If you don't have a due date yet, but you just had an early dating ultrasound (e.g., you were told you were exactly 8 weeks and 2 days pregnant on Tuesday), we can use that data. Early ultrasounds are the most accurate way to date a pregnancy. The calculator projects your due date based on the ultrasound measurements, and then subtracts 266 days to find the conception date.
Conception Date vs. Intercourse Date
It's vital to remember that the day of conception is the day the egg is released (ovulation) and fertilized. This is not necessarily the day you had intercourse! Because sperm can survive in the reproductive tract for up to 5 days, intercourse any time in the 5 days before conception, through the day of conception itself, could be responsible for the pregnancy.
This tool is for personal reference and educational purposes only, not medical advice or legal proof of paternity. Talk to your healthcare provider for confirmed pregnancy dating.
Frequently Asked Questions
Doctors rarely give an exact conception date because it's medically difficult to prove the exact moment a sperm fertilized an egg. Instead, they date the pregnancy starting from your last menstrual period (LMP) or by measuring the fetus during an early ultrasound.
Not always! Sperm can survive inside the female reproductive tract for up to 5 days. You could have intercourse on a Monday, but the actual conception (fertilization) might not happen until you ovulate on Friday.
Because pregnancy math starts at the first day of your last period, 'Week 1' and 'Week 2' occur before you have even ovulated or conceived. True conception usually happens exactly 2 weeks after the start of a 28-day cycle.
It reflects the roughly 5 days sperm can survive before ovulation, but real timing varies by person and cycle. Treat it as a reasonable estimate rather than a precise record.
Both methods assume a fairly typical cycle length, so irregular ovulation timing can shift your real conception date earlier or later than shown. An early ultrasound remains the most reliable way to date a pregnancy.
No. This tool gives a personal-reference estimate only — it is not proof of paternity or a substitute for certified genetic or medical testing.
Almost certainly not exactly. Only around 5% of babies are born on their precise due date, so it's best to think of both your due date and conception estimate as a range rather than a fixed day.
No. This calculator is for personal reference only. For confirmed pregnancy dating, always talk to your doctor or midwife, especially since early ultrasound dating is more accurate than this kind of estimate.