How DNA matching works is one of the most important concepts to understand when using DNA for genealogy. A DNA match is another person whose DNA contains enough shared genetic material with yours to suggest that you may share a common ancestor.

DNA matching can help you find relatives, investigate unknown branches of your family tree, test traditional genealogy research, and generate new clues when historical records reach a dead end.

But a DNA match is not automatically proof of a specific relationship. To understand what a match means, you need to look at the amount of shared DNA, the number and size of shared segments, family trees, surnames, locations, and other evidence.

How DNA Matching Works: Quick Overview

At a basic level, DNA matching works by comparing parts of your DNA with the DNA of other people who have tested with the same service or whose data has been made available through that service.

When enough DNA appears to be shared, the testing company identifies the person as a potential DNA match and estimates a possible relationship.

1. You take an autosomal DNA test or use eligible DNA data.
2. The testing service analyzes your DNA.
3. Your DNA is compared with other participants.
4. Shared DNA segments are identified.
5. The amount of shared DNA is measured, commonly in centimorgans (cM).
6. The service estimates possible relationships.
7. You investigate the match using genealogy evidence.

The exact algorithms, thresholds, databases, and features vary between companies, so the same person may not appear as a match on every DNA testing platform. MyHeritage, for example, notes that matching algorithms and thresholds can vary between providers.

Why DNA Matching Matters for Genealogy

Traditional genealogy relies heavily on records such as birth certificates, census records, church registers, marriage records, immigration documents, and other historical sources.

DNA can provide another type of evidence. Suppose your family tree suggests that two branches connect through a particular ancestor. A DNA match with a person who descends from that same family line can provide supporting evidence.

DNA can also help when records are missing, contradictory, difficult to locate, or unavailable because of an adoption, name change, migration, or other circumstance.

What DNA Matching Can Help You Do

• Find biological relatives: Discover people who may belong to branches of your family.
• Test genealogy theories: Look for DNA evidence that supports a proposed relationship.
• Identify unknown family branches: Use clusters of matches to investigate an unfamiliar surname or location.
• Break through brick walls: Generate new research leads when traditional records stop.
• Investigate unknown parentage: DNA matches can sometimes provide important clues about biological family connections.

How DNA Matching Works Step by Step

Understanding Centimorgans (cM)

If you are learning how DNA matching works, centimorgans are one of the first concepts you should understand.

A match might share a relatively large amount of DNA with you or a much smaller amount. In general, larger amounts of shared DNA are associated with closer relationships, while smaller amounts can indicate more distant relationships. However, the same amount of shared DNA can sometimes be consistent with several different relationships.

For example, a particular cM total should not automatically be interpreted as proof that someone is your third cousin, fourth cousin, or another exact relationship. Instead, use the cM value to create a range of possible relationships and then investigate the genealogy evidence.

The Shared cM Project, a collaborative research project led by Blaine Bettinger, provides observed ranges of shared DNA for nearly 50 different genealogical relationships, based on tens of thousands of submissions from genealogists. The DNA Painter Shared cM Tool makes this data accessible as an interactive visualization. MyHeritage also provides example average ranges for relationships such as parents, siblings, grandparents, aunts/uncles, and first cousins, while emphasizing that actual shared DNA values can be higher or lower.

Three Numbers to Pay Attention To

Depending on the DNA testing company, you may see several measurements associated with a match.

MyHeritage specifically uses shared DNA, shared segments, and the largest segment as parameters for evaluating DNA matches.

How DNA Companies Predict Relationships

DNA testing companies use the amount and pattern of shared DNA to estimate a possible relationship. You might therefore see descriptions such as:

• Parent or child
• Sibling or close family
• Aunt, uncle, niece, or nephew
• Cousin relationships
• Distant relative

The exact labels and relationship ranges vary between providers. A predicted relationship should therefore be treated as a starting point for research rather than a guaranteed identification.

Why Relationship Predictions Can Be Ambiguous

DNA inheritance is random because recombination shuffles genetic material during the formation of egg and sperm cells. According to the ISOGG Wiki, recombination is the exchange of DNA segments between the two copies of a chromosome, and each chromosome is cut at one or two random spots. You do not inherit exactly the same amount of DNA from every ancestor at the same generational distance. This means that two relatives with the same genealogical relationship can share different amounts of DNA. Research published in the journal Genetics further demonstrates that recombination patterns vary across the genome and between individuals, contributing to this uncertainty [Identity by descent: variation in meiosis, across genomes, and in populations].

As relationships become more distant, there can also be more uncertainty about whether a small shared segment represents a genealogically meaningful connection.

Are Small DNA Matches Useful?

Small DNA matches can sometimes be useful, but they require more careful analysis than stronger matches. A small match may represent a genuine distant relationship, but small segments can also be less informative and may sometimes result from shared DNA that does not come from a recent common ancestor.

MyHeritage specifically warns that very small matches can sometimes represent identity by state (IBS) rather than identity by descent (IBD), particularly among more distant matches. The ISOGG Wiki defines identity by state as alleles that are the same irrespective of whether they are inherited from a recent ancestor, whereas identity by descent refers to segments inherited from a common ancestor without intervening recombination.

This is why a small match should normally be considered together with other evidence such as shared surnames, locations, family trees, and additional shared matches.

What Are Shared DNA Matches?

One of the most useful features for genealogy is the ability to identify people who match both you and another DNA match. These are often called shared matches. Shared matches can help you determine which side of your family a DNA match may belong to. MyHeritage describes shared DNA Matches as people who are genetically related to both you and your DNA match, and notes that they can help identify which side of the family a match may be connected to.

For example, imagine that you have a known maternal cousin who appears as a match with another person. If that other person also shares DNA with your known maternal cousin, the shared-match pattern can provide a clue that the new match may belong to your maternal side. It does not prove the exact relationship, but it can help narrow your research.

MyHeritage describes shared DNA matches as people who are genetically related to both you and your DNA match, and notes that they can help identify which side of the family a match may be connected to. The feature shows matches that are the closest, on both the paternal and the maternal side, with the closest estimated relationships at the top of the list.

Why Family Trees Matter When Analyzing DNA Matches

DNA tells you that two people may be related. A family tree can help explain how. When reviewing a DNA match, look for:

• Shared surnames
• Shared ancestral locations
• Common ancestors
• Overlapping family-tree branches
• Shared matches
• Migration patterns
• Historical records supporting the proposed connection

A DNA match with a detailed public family tree can therefore be much easier to investigate than a match with no genealogical information. This is one reason why building your own family tree before or after taking a DNA test can make your DNA results much more useful.

Our beginner's guide to genealogy research can help if you are also learning traditional family-history research.

DNA Matching Tools You Can Use

Once you understand the basics of how DNA matching works, specialized tools can help you analyze your matches more effectively.

What Is a Chromosome Browser?

A chromosome browser is a tool that can show where shared DNA segments occur along chromosomes. The ISOGG Wiki describes it as a tool that allows comparison between one or more matches to see which segments of DNA are shared in common and their locations. This can be particularly useful when you move beyond basic match lists and begin investigating whether multiple people share the same segment.

MyHeritage describes its Chromosome Browser as a visual tool for locating shared DNA segments between people. For a practical introduction, try our free DNA Chromosome Browser. You can also continue to our more advanced guide to DNA triangulation.

What Is DNA Triangulation?

DNA triangulation is an advanced technique in which you investigate whether you and multiple DNA matches share the same DNA segment with one another. The ISOGG Wiki explains that in autosomal DNA testing, triangulation is the term used to describe the process of reviewing the pedigree charts of people who match on the same IBD autosomal DNA segment to see if a common ancestor can be found.

If three or more people share the same relevant segment, and the genealogy evidence points toward the same family branch, this can provide a stronger research clue about a possible common ancestor.

Triangulation is more advanced than simply looking at your list of DNA matches, so beginners should first become comfortable with shared DNA, cM, family trees, and shared matches. When you are ready, read our advanced DNA triangulation guide.

Common DNA Matching Mistakes to Avoid

How to Analyze a DNA Match: Beginner Workflow

Once your DNA results are available, use a consistent process rather than opening matches randomly.

For a much more advanced approach, see our guide to analyzing DNA matches, where we go deeper into DNA research strategies.

Use Our Free DNA Relationship Calculator

If you know how much DNA you share with a match, our DNA Relationship Probability Calculator can help you explore possible relationships. Remember that a calculator provides possibilities rather than a definitive identification. Use the result together with family-tree evidence and historical research.

DNA Matching and Privacy

DNA is highly personal information, so privacy should be part of your genealogy research strategy. Before testing or uploading DNA data, review the current privacy controls of the service you plan to use. Check how the service handles:

• DNA matching participation
• Research participation
• Sharing of DNA information
• DNA data deletion
• Account management
• Access to DNA matches

For example, MyHeritage currently provides DNA privacy settings that allow users to control participation in DNA Matching and certain shared-segment features. MyHeritage states that it will not sell or license genetic data without explicit consent and prohibits law enforcement use of its DNA Services.

Take Your Research Further on Genetic Voyage

Frequently Asked Questions About DNA Matching

Final Thoughts

Understanding how DNA matching works gives you a foundation for genetic genealogy. A DNA match can open a door to a previously unknown relative, but the real research begins when you investigate the evidence behind the match.

Start with the amount of shared DNA, examine the available family-tree information, look for shared matches, and then test your theories against reliable historical records. With practice, DNA matching can become one of the most powerful tools in your genealogy research toolkit.