When looking at a conception calculator and it gives a specific date that someone couldve conceive, what is the plus or minus the days of accuracy?

The calculators will give estimates and give no guarantees of the actual date of conception. It is an approximation. It really makes no difference as to the actual date you conceived unless you had multiple partners with unprotected intercourse during that time and you are trying to determine who the father is. If that is the case, you would probably be better off to do paternity tests.