The expected relationship between you and your Y-chromosome DNA (Y-DNA) match is dependent on both the number of markers you have tested and the genetic distance. The chart below shows the interpretation of your relationship at each testing level (Y-DNA12, Y-DNA37, etc.) for relevant genetic distances.

For example, if you and your match have both tested at the Y-DNA37 level and are a 36/37 match, this is a genetic distance of one. You are then considered tightly related.

Y-DNA12 Y-DNA25 Y-DNA37 Y-DNA67 Y-DNA111 Interpretation
Very Tightly Related N/A N/A 0 0 0 Your exact match means your relatedness is extremely close. 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.
Tightly Related N/A N/A 1 1-2 1-2 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.
Related 0 0-1 2-3 3-4 3-5 Your degree of matching is within the range of most well-established surname lineages in Western Europe. If you have tested with the Y-DNA12 or Y-DNA25 test, you should consider upgrading to additional STR markers. Doing so will improve your time to common ancestor calculations.
Probably Related 1 2 4 5-6 6-7 Without additional evidence, it is unlikely that you share a common ancestor in recent genealogical times (one to six generations). You may have a connection in more distant genealogical times (less than 15 generations). If you have traditional genealogy records that indicate a relationship, then by testing additional individuals you will either prove or disprove the connection.
Only Possibly Related 2 3 5 7 8-10 It is unlikely that you share a common ancestor in genealogical times (one to 15 generations). Should you have traditional genealogy records that indicate a relationship, then by testing additional individuals you will either prove or disprove the connection. A careful review of your genealogical records is also recommended.
Not Related 3 4 6 >7 >10 You are not related on your Y-chromosome lineage within recent or distant genealogical times (one to 15 generations).
UnderstandingMatches