Obstetrics

Estimated Conception Date

Estimates date of conception from last menstrual period (assuming 28-day cycle).

When to use: Useful for medicolegal purposes, paternity timelines, or counselling around exposure to teratogens. Conception typically occurs around day 14 of a regular 28-day cycle (14 days after LMP start).

Calculator

Days since first day of LMP(days)

Fill in all fields to see the result

Formula

Conception ≈ LMP + 14 days (ovulation on day 14 of 28-day cycle) Fertilisation window: days 10–17 of cycle (sperm viability ~5 days)

Key Points for NEET PG

Ovulation occurs ~14 days before next period — day 14 in a 28-day cycle, day 21 in a 35-day cycle
Fertile window: 5 days before ovulation + day of ovulation (6 days total)
hCG detectable in urine ~10–14 days after conception (day 24–28 of cycle)
Early pregnancy: hCG doubles every 48–72 hours; failure to double suggests miscarriage or ectopic
Ectopic pregnancy most common in ampullary portion of fallopian tube (~70%)

References

Timing of Sexual Intercourse in Relation to Ovulation · NEJM (1995)

For educational purposes only. Not for clinical decision-making without professional oversight.