If your relationship is within recent generations (2nd cousins or more recent relatives), Family Finder is almost sure to detect your relationship. Testing will also detect many 3rd cousins and about half of your 4th cousins. It will detect a small percentage of 5th and more distant cousins.

Chances of finding a match:
Relationship Match Probability
2nd cousins or closer > 99%
3rd cousin > 90%
4th cousin > 50%
5th cousin > 10%
6th cousin and more distant Remote (typically less than 2%)

For example, if you have 100 of your 3rd cousins test, Family Finder will detect about 90 of them as your 3rd cousins. It will not detect the other 10.

Family Finder only detects a small percentage of 5th cousins and relatives that are more distant. However, the number of such cousins in the population increases exponentially with each generation. This means that if 1,000 of your distant cousins test, you can expect to see a few of them in the Speculative Relative category.

For genealogists, it is best to use Family Finder to prove recent relationships (1 to 5 generations). However, after testing, you may discover distant cousins.