Approximately 3rd June. However u won't get an accurate result until you have your dating scan. When you have the dating scan they will tell you how far gone you are. To work out when you conceived you need to work out the date when you would have been 2 weeks pregnant. So for example if you have your dating scan on 29th July and they said you were 10 weeks 3 days (just an example), then count back to when you would have been 2 weeks pregnant and you would have conceived around 31st June.
Hope that helps!
count back about 4 weeks from 1st july