Had sex 12/8 period came on 12/20. normal cycle 31 days. then i had sex 1/3, 9, 13, 10 most likely when did i conceive? should have started 1/20 today

Unclear: Given the information provided, my best estimate would be january 9/10 or possibly december 8th. However to know if your are in fact pregnant, get a pregnancy test. A quantitative blood HCG rather than a urine test is needed to estimate conception date. It measures the amount of a hormone that regularly increases during the first trimester.