Key points
- Conception means fertilisation near ovulation, not the day you had sex. The fertile window spans six days and ends on ovulation day.
- Sperm can survive in the reproductive tract for up to five days, so sex before ovulation can lead to conception later.
- Implantation happens later again, most often 8–10 days after ovulation.
- Home urine tests turn positive only after implantation raises hCG, so accuracy is best on or after the first missed period.
Quick converter: intercourse, conception, due date
Assumptions: this simple tool uses conception = intercourse + 2 days, and EDD = conception + 266 days. You can change the default 2-day offset in the code.
Tip: For a full calculator with options, open the Due Date from Conception or Intercourse tool.
What “conception date” means
“Conception date” is the day fertilisation occurred, usually within hours of ovulation in the fallopian tube. It usually aligns with ovulation day, not the intercourse day.
Why intercourse date often differs
Sperm can live up to five days in the right cervical mucus. This is why clinicians speak about a six-day fertile window. If you have sex on Monday and ovulate on Thursday, fertilisation can occur on Thursday, several days after intercourse.
Implantation comes later
After fertilisation, the embryo travels to the uterus and implants. Most successful pregnancies implant 8–10 days after ovulation, with normal variation. Home urine tests detect hCG after implantation, so the first reliable day to test is around or after the missed period for many people.
A simple timing example
- Intercourse: Monday
- Ovulation: Thursday
- Conception (fertilisation): Thursday
- Implantation: the following week, often 8–10 days after ovulation
- First reliable urine test: on or after the first missed period
Working out dates on our site
If you know your due date, work backwards to a likely conception and intercourse window with the reverse tool. If you have a scan date and gestational age, you can set an EDD and cross-check today’s weeks.
FAQs
Can the conception date ever match the intercourse date?
Yes, if intercourse occurs on ovulation day and fertilisation follows soon after. It often does not, because sperm can wait in the tract for several days until ovulation.
Which date do clinicians use to date a pregnancy?
Clinicians usually date pregnancy from the last menstrual period or from early ultrasound, then derive the EDD. If you prefer a conception-based view, start with our Pregnancy Due Date Calculator or Reverse Due Date.
When should I test?
Home urine tests are most reliable on or after the first missed period because hCG rises only after implantation. See day-by-day performance in the Pregnancy Test Accuracy Calculator.
Worried about a specific encounter?
Use Pregnancy Chance After Unprotected Intercourse for a per-incident estimate and timing guidance.
Sources
- Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. N Engl J Med. 1995. PDF
- Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med. 1999. PDF Abstract
- American College of Obstetricians and Gynecologists. Trying to get pregnant? Here’s when to have sex. ACOG
- Office on Women’s Health. Pregnancy tests fact sheet. PDF
- Mayo Clinic. Home pregnancy tests: Can you trust the results? Mayo Clinic