What Is a DNA Match?
A DNA match is another tested individual who shares one or more segments of DNA with you that are identical by descent — meaning inherited from a common ancestor. Testing companies identify these shared segments by comparing the specific locations across both people's genomes where the same version of a genetic marker appears. The more segments you share, and the longer those segments are, the more recently you share a common ancestor.
Shared DNA is measured in centimorgans (cM), a unit that reflects the length of shared genetic segments adjusted for the probability of recombination. Full siblings share approximately 2,550 cM on average, while first cousins share approximately 850 cM on average. As relationships become more distant, the amount of shared DNA decreases and the variation around the average increases, making distant relationship predictions less certain.
Interpreting Relationship Predictions
Close Matches
Parents and children share approximately 3,500 cM. Siblings share 2,300–3,900 cM. Grandparents/grandchildren share 1,200–2,400 cM. These close relationships are identified with high confidence by all testing companies.
First & Second Cousins
First cousins share 550–1,250 cM. Second cousins share 40–650 cM. The wide ranges reflect the random nature of DNA inheritance. Relationship predictions in this range are generally reliable, though the specific relationship (1st cousin vs. half-sibling) may require additional analysis.
Distant Cousins
Third cousins and beyond share smaller amounts with high variability. Many third cousins share 0 cM — no detectable DNA — due to the random inheritance of segments. Among those who do share DNA, amounts range from a few cM to several hundred.
Strategies for Analyzing Your Match List
The most effective approach to working with DNA matches combines genetic and genealogical evidence systematically. Start with your closest matches and work outward. For each match, look at their family tree if they have one public, note any surnames or locations that overlap with your own research, and record what you find. Even small clues from a match's tree can point toward a shared ancestral line.
Leeds method clustering and visual phasing are two powerful techniques for organizing large match lists. The Leeds method groups your fourth-cousin-level matches into clusters that typically correspond to your four grandparent lines, making it easier to identify which family line each match connects to. Once grouped, all the matches in a cluster share a common ancestor on the same line, and their combined trees often reveal that ancestor.
Working With Unknown Parentage
DNA matching is transformative for individuals researching unknown parentage — adoptees, donor-conceived individuals, and those with non-paternity events (NPEs) in their family. The process involves identifying close matches, building trees for those matches, and working backward to find where the trees intersect with the tester's own expected family connections.
This approach, sometimes called "mirror tree" methodology, has helped thousands of Americans identify biological parents and siblings. Success rates are high when close matches are available — the larger the testing database, the more likely close relatives have also tested.
Why do I have so many matches I don't recognize?
Most people have thousands of DNA matches, most of whom are distant cousins. The majority share common ancestors from many generations back, making a specific connection difficult to identify without substantial genealogical research on both sides. Focus on your closest matches first, as these offer the most actionable leads.
How do I contact DNA matches?
Testing platforms provide messaging tools to contact matches. Introduce yourself politely, explain your research goals, and mention any specific surnames or locations you are investigating. Many people who test are actively researching and welcome contact from genetic relatives.
What is a chromosome browser?
A chromosome browser is a tool offered by some testing companies that displays which specific chromosomes and segments you share with a match. This tool helps confirm that multiple matches share the same segment (indicating the same ancestral source) and assists in phasing — assigning each segment to a specific parent's line.