How far apart do sexual encounters need to be to determine paternity? without doing dna test

Paternity testing: It's hard to say exactly & what if there are multiple sex partners. Most of the time, you will not know the exact day you got pregnant. Paternity testing provides "scientific evidence" of whether a man can be the biological father of a child. Paternity is determined by making a comparison of the child's DNA with the DNA profile of the alleged father.