It would be impossible to say at this point because all women do not ovulate at the usual time. There are wide variations and we just take 14 as an average day of the cycle for ovulation. This is how due dates are calculated and day 14 is determined by her menstrual period. Was she on her period at the time you had intercourse?
Estimates are somewhat inaccurate and she may get another date based on an ultrasound exam. These are often more accurate when done fairly early in the pregnancy. The only sure way to know is with a paternity test after the birth of the baby.
Do you have questions about her fidelity other than this date in question? Perhaps you just need to talk about it. Show interest in the pregnancy and share the online sites you were exploring. Tell her you wondered about the dates and ask what she thinks about it. I would ask her when the last menstrual period was, which is usually used to calculate due date. This might help to open the door to conversation. Trust is an important element in a relationship.
The answers in online forums are for information only and are not intended to substitute for medical advice and care. Please see your personal health care provider for further evaluation of your individual case.
Debbie Miller, RN