In cultures where surnames are passed from father to son, there is additional evidence beyond a DNA match that two men who share a surname are related. Y-chromosome DNA (Y-DNA) test results should be interpreted based on both this information and the actual results.

Genetic Distance Relationship Interpretation
0 Very Tightly Related A 37/37 match between two men who share a common surname (or variant) means they share a common male ancestor. Their relatedness is extremely close with the common ancestor predicted, 50% of the time, in five generations or less and over a 95% probability within eight generations. Very few people achieve this close level of a match. All confidence levels are well within the time frame that surnames were adopted in Western Europe.
1 Tightly Related A 36/37 match between two men who share a common surname (or variant) indicates a close genealogical match. Very few people achieve this close level of a match, and it is within the range of most well-established surname lineages in Western Europe. It’s most likely that they matched 24/25 or 25/25 on a previous Y-DNA test, and the mismatch will be found within DYS576, DYS570, or CDY.
2 Related A 35/37 match between two men who share a common surname (or variant) means they share a common male ancestor. The mismatch is likely within the range of most well-established surname lineages in Western Europe. It is most likely that you matched exactly or closely on previous Y-DNA tests, and the mismatch is within DYS439 or DYS385, DYS389i, 389ii, DYS458, DYS459, DYS449, DYS464, DYS576, DYS570, or CDY.
3 Related A 34/37 match between two men who share a common surname (or variant) means they share a common male ancestor. The relationship is likely within the range of most well-established surname lineages in Western Europe. It is most likely that they matched exactly or closely on previous Y-DNA tests, and the mismatch is within DYS439 or DYS385, DYS389i, 389ii, DYS458, DYS459, DYS449, DYS464, DYS576, DYS570, or CDY.
4  Probably Related A 33/37 match between two men who share a common surname (or variant) means they may share a common male ancestor. This relationship should be confirmed with additional testing. The only way to confirm the relationship is to test additional family lines and to find where the mutations took place. By testing additional family lines, you can find the person in between. This ‘in betweener’ is essential for you to find.
5 Possibly Related A 32/37 match between two men who share a common surname (or variant) means that they may be related within the genealogical time frame, but additional evidence is needed to confirm the relationship. If several or many generations have passed since the suspected common ancestor, it is possible that these two men are related. That would require that each line had experienced separate mutations and line would have experienced at least two mutations. The only way to confirm is to test additional family lines and find where the mutations took place. By testing additional family members, you can find the person in between each of you. This ‘in betweener’ becomes essential for you to find, and without him the possibility of a match exists, but further evidence must be pursued.
6 Not Related A 31/37 match between two men who share a common surname (or variant) means that they are not likely to be related within the genealogical time frame. The common surname is a coincidence. If there is a strong family tradition of a relationship, it is distantly possible that these two men are related. That would require that each line had experienced separate mutations and the line would have experienced at least two mutations. The only way to confirm the relationship is to test additional family lines and find where the mutation took place. By testing additional family members, you can find the person in between the two men. This ‘in betweener’ becomes essential for you to find, and without him a genealogical relationship is unlikely.
>6 Not Related The two men are totally unrelated within the genealogical time frame on their direct paternal line. Their shared ancestry is deeply anthropological and dates to the common African heritage of the human race.