Hallow Madam, I hope I can be of help to you today. The due date of delivery (DD) is calculated by a formula DD= Last Menstrual Period date (LMP) + 9 months + 7 days. Since you had your LMP on 10 July 2010, the DD would be on 17 April 2011. If DD provided to you is by ultrasonography, a variation of one week is acceptable as Ultrasonography calculated DD is by the size of the baby and is calculated from the date of conception. To calculate the date of egg release (ovulation), it happens 14 days before the next expected menses. So considering your menstrual cycle of 30 or 31 days, next menses would be on 10 August and ovulation would be on 28 July 2010. The life of an egg is 24 hours and the sperms are active for 72 hours. Hence a period of one week around the ovulation is fertile period. So your fertile period would be 24 July to 1 August. Thus the conception would be in that period. Now in this calculation, you have to make some modifications depending on the periodicity of your menstrual cycle. Then you can locate your fertile period of that cycle. Thus the intercourse(s) during this fertile period are likely to cause the pregnancy. If you had a solitary intercourse during fertile period, that day or within 4 days of that day would be the day of conception. Of course this all is based on the clinical calculations. If you want to ascertain the paternity of your child for any legal cause, you may go for DNA test which would be a fool proof evidence. I hope this helps you. Dr. Nishikant Shrotri