Why Don't I Match a Known Relative?

For anything more distant than a second cousin, not matching is normal — about 10% of third cousins share no detectable DNA at all, rising to roughly half of fourth cousins. That's the answer in most cases, and it isn't a fault in the test or a problem with the family tree. There are other explanations too: you tested with different companies, one of you is below a display threshold, or the relationship is more distant than assumed. Occasionally it does mean the documented relationship isn't biological — and that possibility deserves careful handling rather than a hasty conclusion. This page works through the causes in order of likelihood. The DNA match calculator shows what you'd expect to share.

How Often Do Real Relatives Not Match?

More often than most people expect, and the probability rises steeply with distance.

Why this happens: recombination is random. You inherit exactly half your DNA from each parent, but which half is chance. Going back generations, some ancestors' contributions shrink to nothing. By the fifth-great-grandparent level, most of your ancestors have contributed no detectable DNA to you at all — and two cousins can descend from the same couple while inheriting entirely non-overlapping pieces.

So a missing match at fourth cousin level tells you nothing. It's a coin flip. The absence carries no information about whether the paper trail is correct.

Where it does mean something: first cousins and closer always share substantial DNA. Second cousins virtually always match. If a documented close relationship shows no match at all, there's an explanation to find — and the first places to look are technical rather than genealogical. The expected amounts are set out in how much DNA do cousins share.

What Are the Technical Explanations?

Check these before concluding anything about the family.

You tested with different companies. By far the most common cause. AncestryDNA, 23andMe, MyHeritage and FamilyTreeDNA each hold separate databases and don't compare against each other. Two relatives who tested at different companies are invisible to one another, however closely related.

The fix: most companies allow you to upload raw data from elsewhere, and GEDmatch exists specifically to compare across companies. Uploading a single raw data file to two or three additional services costs little or nothing and frequently produces the missing match immediately.

One of you hasn't opted into matching. Some services require you to actively enable DNA relative matching, and health-focused customers often haven't. It's a checkbox.

Different accounts or profiles. Someone managing tests for several family members can easily be looking at the wrong kit.

The match is below the display threshold. Sites typically don't show matches under roughly 6 to 8 cM. A genuine but small connection may exist and not be displayed, which is common for distant relationships — the underlying unit is explained in centimorgans explained.

Processing delays. New results can take days to fully populate a match list, and matches occasionally appear or disappear as companies update their matching algorithms.

Privacy settings. A match may have limited visibility or opted out of appearing in lists.

Different testing chip versions. Companies have changed their chips over the years, and comparison across versions is occasionally imperfect, particularly for very small segments.

What Genealogical Explanations Should You Consider?

Once the technical checks are clear, look at the relationship itself.

The relationship is more distant than believed. Family terminology is loose — "cousin" covers a great deal of ground, and a "second cousin" is frequently a second cousin twice removed, or a third cousin. Work out the exact relationship from the common ancestor before deciding a match is missing.

It's a half relationship. Half cousins share roughly half what full cousins do, which pushes distant half relationships well into the no-match zone.

It's a step or adoptive relationship. Entirely real as a family relationship, and carries no shared DNA. This is a surprisingly common explanation once you go back a couple of generations and family memory has smoothed over the details.

The paper trail has an error. Someone in the intervening generations may not be who the records suggest — a misattributed parent in a tree copied from another tree, a wrong marriage, two people of the same name conflated.

An unrecorded change of parentage. Adoption, informal fostering, a child raised by grandparents as their own, or a misattributed biological father. Historically common, frequently undocumented, and often unknown to everyone living.

A note on that last one. It's real, it's not rare, and it's also the explanation people jump to fastest and should reach for last. Rule out the technical causes, confirm the exact relationship, and check whether a no-match is statistically expected before drawing any conclusion. Most "non-paternity" panics dissolve on discovering the two people tested at different companies.

How Should You Investigate?

A sensible order:

1. Confirm the exact relationship. Count generations from the common ancestor properly, and check for removals and half relationships.

2. Check the expected probability. If it's a fourth cousin, stop — a no-match is a coin flip and means nothing.

3. Confirm you tested at the same company. If not, upload raw data to a shared platform such as GEDmatch and compare there.

4. Check matching is enabled on both accounts, and that you're both looking at the right kits.

5. Search the match list directly by name and username rather than scrolling. A small match may be buried hundreds of entries down.

6. Look at shared matches. If you don't match your supposed second cousin but you both match several of the same people, the family connection is real and something else is going on — see what are shared DNA matches.

7. Test more relatives. A sibling, aunt or uncle may match where you don't, particularly at third and fourth cousin level. This is often the quickest way to confirm a line is genuine.

8. Only then consider a genealogical explanation, and start with the least dramatic possibilities.

If it turns out to be significant, take time before acting. Unexpected parentage findings affect living people, and there's no obligation to raise it immediately or at all. Consider who has a right to know, who would want to, and what the person concerned would have wanted. Support groups and counsellors experienced in DNA discoveries exist for exactly this, and they're worth using — the general landscape of misconceptions is covered in DNA testing myths.

What About the Opposite — Matching Someone You Shouldn't?

The mirror-image problem, and it has its own set of dull explanations.

Small matches are frequently meaningless. Below about 10 cM, a substantial proportion of reported matches don't reflect a recent common ancestor at all. They're population-level sharing, or artefacts of how the matching algorithm handles regions where your two parents' chromosomes look similar. A 7 cM match with a stranger usually means nothing.

You may be related in a way nobody recorded. Two families in the same parish for two centuries are almost certainly connected several times over, even if no tree shows it. Unexpected matches within a region are ordinary rather than mysterious.

Endogamy produces matches everywhere. In populations that intermarried over generations, people share DNA through many distant paths at once, so match lists are enormous and the amounts overstate closeness considerably.

Double relationships. If two siblings from one family married two siblings from another, or grandparents were cousins, descendants share more than the nominal relationship suggests — sometimes enough to look like a much closer connection.

Or the match is real and your tree is wrong. An unexpected close match — anything above a few hundred cM — is worth taking seriously. That's the level at which the connection is genuinely recent, and a documented tree that can't accommodate it deserves re-examination.

The general rule works in both directions: small numbers mean little, large numbers mean a great deal, and the technical explanations should be exhausted before the dramatic ones.

What Should You Expect From DNA Testing Generally?

Calibrating expectations prevents most of the distress this question causes.

DNA testing is excellent at close relationships and unreliable at distant ones. Within three generations it's essentially definitive. Beyond five, absence of evidence is routine.

Your match list is a sample, not a census. It shows relatives who happened to test, at your company, with matching enabled, above the threshold. Vast numbers of genuine relatives are missing for reasons that have nothing to do with genealogy.

Trees and DNA answer different questions. DNA can confirm or refute a relationship where it's close enough to be detectable; documents establish who people were and how they connect. Neither replaces the other.

Confirming a line usually needs several matches, not one. A single missing match proves little; a pattern across a whole branch means more — and triangulation is what turns a pattern into evidence, as covered in what are triangulated groups.

The honest summary: for most people asking this question, the answer is that the relationship is more distant than they thought, they tested at different companies, or both. Work through the checks in order and the great majority of cases resolve without any family revelation at all.

Frequently Asked Questions

Why doesn't my third cousin show up as a DNA match?

Roughly 10% of third cousins share no detectable DNA, so a missing match at that level is entirely normal. Check first that you both tested at the same company — separate databases don't compare against each other.

Do all second cousins share DNA?

Effectively yes — second cousins share DNA in over 99% of cases, typically around 229 cM. If a documented second cousin shows no match, check for different testing companies, disabled matching, or an error in the assumed relationship before anything else.

Can two people be related and share no DNA?

Yes, and it becomes likely with distance. About half of fourth cousins share nothing detectable, rising to over 95% by sixth cousins. Recombination is random, so some ancestral lines simply aren't passed down to a given descendant.

Why can't I see my relative who tested with a different company?

Because each testing company maintains a separate database and doesn't compare against the others. Uploading raw data to a service that accepts transfers, or to GEDmatch, lets you compare across companies and often produces the match immediately.

Does a missing match mean a non-paternity event?

Usually not. Check the exact relationship, the statistical likelihood, and whether you tested at the same company first. Most cases resolve as a more distant relationship than assumed or as separate databases. Unexpected parentage is real but should be the last explanation considered.

How can I confirm a family line if the match is missing?

Test other relatives — a sibling, aunt or uncle may match where you don't. Look at shared matches, since matching the same group of people confirms the connection even without a direct match, and use documents to establish the paper trail independently.

If there's one habit worth building, it's checking the expected probability before reacting. A great deal of unnecessary anxiety in genetic genealogy comes from treating every absence as meaningful, when the mathematics says most absences are noise. Look up what you'd expect for the exact relationship first, and the question usually answers itself in under a minute.

Start from the statistics rather than the worry. At third cousin and beyond, no match is ordinary; at second cousin and closer, look at testing companies and account settings before anything else. Most of these questions have a dull technical answer, and the dull answer is usually the right one. Check what you'd expect to share for any relationship with the DNA match calculator.