Compare dates of sex with an early ultrasound estimate. See where the timing overlaps for each partner; calendar dates cannot confirm who the father is.
* The displayed range is an approximate timing comparison, not a paternity test or a guaranteed conception window. Neither overlap nor being outside the range proves or excludes paternity. Use DNA testing for confirmation.
How to use
- Enter the first-trimester scan date and the gestational weeks and days from the crown-rump-length estimate.
- Add sex dates and label each Partner A, B or C. You can use several dates for the same partner without entering names.
- Calculate to see a date-ordered comparison. Do not use the result to decide paternity.
Why can two partners both overlap?
Ultrasound does not give an exact fertilization day, and sex can precede fertilization by several days. Partners with nearby dates can both fit the same estimated range. Even one overlapping date does not prove paternity. Discuss an appropriate DNA test with a qualified provider.
Methodology
The dating midpoint is scan date minus gestational age in days plus 14 days, reflecting the conventional difference between gestational and conception age. The displayed conception range extends 7 days either side, using the broader end of ACOG's first-trimester CRL dating accuracy. Each sex date is compared as a possible interval from that date through 5 days later, allowing for sperm survival. Overlapping intervals are labeled as overlap, without probabilities. This is a timing aid derived from dating conventions, not a validated paternity classifier.