How DNA Matching Works

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

Step 1: You Take a DNA Test

Most consumer genealogy matching begins with an autosomal DNA test. Autosomal DNA comes from both sides of your family, making it useful for finding relatives across many branches of your family tree. For example, a person can potentially match relatives connected through their mother’s family as well as relatives connected through their father’s family. If you are new to DNA testing, start with our guide to getting started with DNA testing for genealogy.

Step 2: Your DNA Is Analyzed

The testing company analyzes selected genetic markers from your sample. Consumer DNA testing commonly examines large numbers of genetic positions called SNPs (single nucleotide polymorphisms). The company then uses this information for features such as DNA matching and ancestry analysis.

Step 3: Your DNA Is Compared With Other Testers

The service compares your genetic data with the data of other people in its matching database who are eligible to participate in DNA matching. Ancestry explains that its DNA Matches are generated by comparing your DNA with other people who have opted into matching and are likely to be related based on the comparison. Other providers use their own databases, algorithms, and matching thresholds.

Step 4: Shared DNA Segments Are Identified

When two people have matching stretches of DNA, those sections can be identified as shared DNA segments. These segments may have been inherited from a common ancestor. MyHeritage describes shared DNA segments as sections of DNA that are identical between two individuals and notes that they were most likely inherited from a common ancestor.

Step 5: Shared DNA Is Measured

The amount of shared DNA is commonly expressed in centimorgans (cM). In general, close relatives share more DNA than distant relatives. However, there is considerable variation in the amount of DNA inherited from different ancestors, so cM should be treated as evidence for a range of possible relationships rather than an exact answer.

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. MyHeritage 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.

• Total shared DNA: The total amount of DNA shared with the match.
• Number of shared segments: How many separate DNA segments you share.
• Largest shared segment: The size of the largest individual shared segment.

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. 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. 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 rather than identity by descent, particularly among more distant matches. 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. 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.

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.

DNA Testing Company Match Tools

Major genealogy DNA services provide their own matching systems. Depending on the provider, you may be able to examine shared DNA, predicted relationships, family trees, shared matches, and other information.

MyHeritage DNA Matching

MyHeritage combines DNA matching with family-tree information and other genealogy features. Its DNA Match pages can provide information such as shared DNA, shared segments, largest segments, possible relationships, shared surnames, shared matches, and pedigree information. MyHeritage also allows DNA matching for eligible DNA data uploaded from certain other services, according to its current help documentation.

AncestryDNA

AncestryDNA provides DNA Matches based on comparisons between people who have tested and participate in DNA matching. Its DNA matching system includes predicted relationship categories and shared DNA information. Ancestry also provides additional genealogy resources that can be used alongside DNA research.

FamilyTreeDNA

FamilyTreeDNA is particularly relevant to researchers interested in genetic genealogy, including autosomal DNA as well as specialized Y-DNA and mtDNA testing. For beginners, autosomal DNA is generally the most relevant starting point for finding relatives across multiple branches of a family tree.

GEDmatch

GEDmatch is a separate genealogy DNA platform that can be used for additional DNA analysis. Features and access levels can change, so check the current platform information before relying on a particular tool.

What Is a Chromosome Browser?

A chromosome browser is a tool that can show where shared DNA segments occur along chromosomes. 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. 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

1. Assuming the Predicted Relationship Is Exact

A predicted relationship is an estimate. Treat it as a research hypothesis and investigate other possibilities.

2. Looking Only at Total cM

Total shared DNA is important, but the number and size of shared segments and the wider genealogy context can provide additional information.

3. Ignoring Family Trees

A DNA match without genealogical context can be difficult to identify. Family trees, surnames, locations, and records can transform a match into a useful research lead.

4. Treating Every Small Match as Proof

Small matches can be useful, but they need more supporting evidence. Very distant matches can be difficult to interpret confidently.

5. Ignoring Shared Matches

Shared matches can help you determine which branch of your family a new match may belong to.

6. Forgetting Traditional Genealogy

DNA should not be treated as a replacement for documentary research. Whenever possible, verify a proposed relationship using historical records.

How to Analyze a DNA Match: Beginner Workflow

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

1. Start with stronger matches. These are generally easier to interpret.
2. Record the shared DNA. Note the total cM and other available measurements.
3. Look at the family tree. Search for surnames, locations, and potential ancestors.
4. Check shared matches. Determine whether the match connects to known relatives.
5. Identify a possible family branch. Use the evidence to narrow down where the match belongs.
6. Search historical records. Test the proposed connection against documentary evidence.
7. Record your conclusion. Keep notes so you can return to the match later.

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.

Frequently Asked Questions About DNA Matching

How does DNA matching work?

DNA matching works by comparing your genetic data with that of other people in a DNA database. When enough relevant DNA is shared, the service identifies the person as a potential match and estimates a possible relationship.

What does a DNA match mean?

A DNA match generally means that you and another person share enough DNA to suggest a possible biological relationship. The match does not necessarily identify the exact relationship or common ancestor by itself.

What is shared DNA?

Shared DNA is genetic material that appears in both your DNA and the DNA of your match. Shared DNA is commonly measured in centimorgans (cM).

What does cM mean in DNA genealogy?

cM stands for centimorgan. It is a unit used to describe genetic distance and is commonly used in genealogy to measure the amount of DNA shared between two people.

Do closer relatives always share more DNA?

Generally, closer relatives share more DNA, but inheritance is random and the amount can vary. Therefore, shared DNA should be interpreted as a range of possible relationships rather than an exact answer.

Are DNA matches always accurate?

DNA matching can be highly useful, but not every match should be treated as proof of a specific relationship. Small or very distant matches can require additional evidence, and different companies can use different matching algorithms and thresholds.

Can DNA matches prove who my ancestor was?

A DNA match can provide evidence supporting a genealogical hypothesis, but identifying a specific ancestor usually requires additional evidence such as family trees, shared matches, historical records, and sometimes chromosome-level analysis.

What should I do after finding a DNA match?

Start by recording the shared DNA and estimated relationship. Then examine the person’s family tree, surnames, locations, shared matches, and other available information. From there, investigate historical records and contact the match when appropriate.

Can I use DNA matching for adoption research?

Yes. DNA matching can provide important clues in unknown-parentage and adoption research. However, these cases can be complex and should be approached carefully, especially when contacting previously unknown biological relatives. See our dedicated DNA testing guide for adoptees for more information.

What to Do Next

Now that you understand how DNA matching works, the next step is learning how to interpret your own matches.

• Learn how to interpret DNA test results
• Use our DNA Relationship Probability Calculator
• Try our free DNA Chromosome Browser
• Learn DNA triangulation
• Read our advanced DNA match analysis guide

If you have not taken a DNA test yet, you can also compare the major providers in our DNA test comparison for genealogy.

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.