What Is a Fourth Cousin? DNA & Family Tree Guide 2026

Ever looked at your DNA match list and wondered what a fourth cousin actually means? In the world of genealogy, a fourth cousin is someone who shares the same great-great-great-grandparents as you, making them a distant but genuine relative in your family tree. These connections bridge nearly two centuries of family history, linking you to ancestors who likely lived in the early to mid-1800s.

Modern DNA testing has transformed how we discover these relationships. Today, platforms like AncestryDNA and 23andMe regularly identify thousands of fourth cousin matches for test-takers, revealing family connections that would have remained hidden just a generation ago. Understanding these distant relationships helps you navigate your genetic genealogy results and appreciate the vast network of relatives that extends far beyond your immediate family circle.

Whether you are building your family tree or simply curious about that unexpected DNA match, this guide will clarify exactly what fourth cousins are, how they connect to you, and what these relationships mean in practical terms.

Cousin Comparison Chart: Understanding the Degrees

Before diving into fourth cousins specifically, it helps to understand how cousin relationships differ by degree. Each step up in cousin degree means one more generation back to find your common ancestors.

Cousin Type	Common Ancestors	Generations Back	Approximate DNA Shared	Average Number
First Cousin	Grandparents	2 generations	12.5% (850 cM)	6
Second Cousin	Great-Grandparents	3 generations	3.125% (220 cM)	28
Third Cousin	2nd Great-Grandparents	4 generations	0.781% (70 cM)	175
Fourth Cousin	3rd Great-Grandparents	5 generations	0.2% (15-20 cM)	1,570

As you can see, fourth cousins represent a significant jump in both generational distance and the number of potential relatives. While you likely know most of your first cousins personally, you have probably never met the vast majority of your fourth cousins.

What Is a Fourth Cousin?

A fourth cousin is a relative who shares great-great-great-grandparents with you, also known as your third great-grandparents. These ancestors sit five generations back in your family tree. The fourth cousin meaning refers to a familial connection where two people descend from the same set of third great-grandparents but through different lines.

To understand this relationship, trace your lineage back five generations. You have parents (1st generation), grandparents (2nd generation), great-grandparents (3rd generation), great-great-grandparents (4th generation), and finally great-great-great-grandparents or third great-grandparents (5th generation). Your fourth cousins are the descendants of your third great-grandparents siblings.

This relationship sits at the edge of what most DNA testing companies can reliably detect. Fourth cousins represent a genuine blood connection, albeit a distant one, and they form a bridge to your deeper ancestry that closer relatives cannot provide.

What Is the Relationship Between Me and My Fourth Cousin?

Your fourth cousin shares ancestors with you from approximately five generations ago. If those third great-grandparents lived around the early 1800s, your fourth cousins today could be scattered across the globe, often unaware of their connection to you.

From a genetic standpoint, fourth cousins carry fragments of the same ancestral DNA you inherited. However, the amount shared is minimal due to the generational distance. Each generation of inheritance shuffles and reduces the DNA passed down, meaning fourth cousins retain only small segments from their common ancestors.

Culturally, the significance of fourth cousin relationships varies dramatically. In some communities, particularly those with strong extended family traditions or endogamous populations, fourth cousins may be recognized and included in family networks. In other societies, these distant connections rarely register as meaningful relationships. The legal standing of fourth cousins also differs by jurisdiction, though most regions treat them as sufficiently distant relatives for purposes like marriage laws.

Which Common Grandparents Do Fourth Cousins Have?

Fourth cousins share great-great-great-grandparents, also called third great-grandparents. This represents five generations of removal from you, not to be confused with the incorrect claim that they share ancestors hundreds of generations back.

To visualize this: imagine your third great-grandparents, a married couple living around 1820 to 1850. They had multiple children. One of those children is your direct ancestor leading to you. Another of their children is the ancestor leading to your fourth cousin. You and your fourth cousin are the great-great-great-grandchildren of that original couple, making you fourth cousins.

This generational distance explains why fourth cousins typically share so little DNA and why discovering these connections often requires both traditional genealogical research and modern DNA testing. The ancestors connecting fourth cousins lived long before photography was common, making documentary evidence challenging but rewarding to uncover.

Do Fourth Cousins Share the Same Bloodline?

Fourth cousins do share a bloodline, but the genetic connection is minimal and sometimes undetectable. Research from genetic genealogy studies indicates that fourth cousins share approximately 0.2% of their DNA, typically ranging from 15 to 20 centimorgans (cM) in shared segments.

However, here is a crucial point: roughly 50% of fourth cousins share no detectable DNA at all. This happens because of the random nature of genetic inheritance. Each parent passes down about 50% of their DNA to each child, but which 50% varies. Over five generations, the probability that any specific DNA segment from a third great-grandparent survived in both lineages drops significantly.

When DNA testing companies like AncestryDNA or 23andMe identify a fourth cousin match, they are detecting those cases where shared segments did survive the generational lottery. A match at this level typically indicates 5 to 10 shared DNA segments, often quite small, that originated from your common third great-grandparents.

How Many Fourth Cousins Could I Possibly Have?

The number of fourth cousins you have depends on several variables, but statistical research from the International Society of Genetic Genealogy (ISOGG) provides useful benchmarks. On average, a person has approximately 1,570 fourth cousins, though this number varies significantly based on family size, cultural background, and historical factors.

Several factors influence your fourth cousin count:

Family size per generation: Ancestors who had large families create exponentially more descendant branches, potentially producing hundreds of fourth cousins from a single third great-grandparent pair.
Endogamy and pedigree collapse: In populations where cousins traditionally married, or where geographic isolation limited partner choice, the same ancestors appear multiple times in your tree. This can multiply your effective fourth cousin count.
Migration patterns: Families that remained in one region for generations often have larger local cousin networks, while those who dispersed globally create more scattered connections.
Historical survival rates: Infant mortality, wars, and epidemics affected different family lines differently, pruning some branches entirely while others flourished.

DNA testing databases provide real-world evidence of these numbers. Many AncestryDNA users report having 1,000 to 3,000 fourth cousin matches, while those from endogamous populations (such as Ashkenazi Jewish, Acadian, or certain isolated communities) may have 5,000 or more detected matches at this level.

Can Fourth Cousins Marry?

Yes, fourth cousins can legally marry in all 50 US states and virtually every country worldwide. The genetic distance between fourth cousins is sufficient that marriage laws pose no restrictions on these unions.

From a genetic perspective, fourth cousin marriages carry minimal increased risk compared to unrelated couples. The shared DNA of approximately 0.2% means both partners carry the same rare recessive gene from their common ancestors only about 0.04% of the time. For context, first cousins share roughly 12.5% of their DNA, which is why their marriages receive more legal scrutiny in some jurisdictions.

Historically, fourth cousin marriages were not uncommon, particularly among European aristocracy and land-owning families seeking to consolidate property while maintaining some genetic diversity. Charles Darwin married his first cousin Emma Wedgwood, and while this was socially acceptable in 19th century England, modern genetics has revealed elevated risks for closer cousin unions that do not apply to fourth cousins.

Today, fourth cousin marriages raise no significant genetic counseling concerns. The consanguinity coefficient for fourth cousins is approximately 0.00195, meaning they share about 1/512th of their genes by descent. This level of relatedness is considered genetically insignificant for reproductive purposes.

Would Fourth Cousins Be Counted as Part of the Family?

Fourth cousins are indeed part of your extended family, though the practical recognition of these relationships varies widely. In genealogical terms, they are blood relatives with documented connections to your ancestry.

The cultural significance of fourth cousins depends on several factors:

In societies with strong extended family traditions, such as many Hispanic, Asian, and Mediterranean cultures, fourth cousins might be acknowledged at large family gatherings or maintained as part of the broader kin network.
In Western individualist cultures, most people have no knowledge of their fourth cousins and would not recognize them as family unless specifically introduced through genealogical research.
Among genealogy enthusiasts and DNA testers, fourth cousins often become valuable research collaborators, sharing family photos, documents, and oral histories that illuminate shared ancestry.

Whether fourth cousins “count” as family is ultimately a personal or cultural determination. Legally, they are distant relatives with no special status for inheritance or medical decisions unless explicitly named in legal documents. Socially, the discovery of a fourth cousin can spark fascinating conversations about shared heritage and family history.

What Does It Mean When We Say ‘Fourth Cousin Once Removed’?

The term “removed” in cousin relationships indicates a generational difference. When someone is your fourth cousin once removed, they are either one generation above or below your fourth cousin level.

There are two possibilities for a fourth cousin once removed:

Your parent’s fourth cousin: This person shares great-great-great-grandparents with your parent (your great-great-great-great-grandparents), making them one generation removed from your direct fourth cousin relationship.
Your fourth cousin’s child: This person is one generation below your actual fourth cousin, hence once removed from your generational level.

The genetic relationship with a once removed cousin differs from a true fourth cousin. Fourth cousins once removed share slightly less DNA on average than true fourth cousins, typically around 0.1% or 10-15 cM, because of the additional generational gap.

What Is the Meaning of ‘Fourth Cousin Twice Removed’?

A fourth cousin twice removed represents a two-generation gap from the standard fourth cousin relationship. This relationship can occur in two directions:

Upward: Your grandparent’s fourth cousin, someone who shares third great-grandparents with your grandparent (your fourth great-grandparents or 4x great-grandparents).
Downward: The grandchild of your fourth cousin, who is two generations below your level.

DNA sharing with fourth cousins twice removed becomes increasingly variable. While some shared DNA may still be detectable, many relationships at this distance show no matching segments at all. The randomness of genetic recombination over seven generations means the odds of retaining common DNA segments drop substantially.

Understanding these removed relationships helps when DNA testing reveals unexpected matches. If AncestryDNA predicts a “4th-6th cousin” relationship, the match could be a fourth cousin, a fourth cousin once removed, or even more distant depending on the amount of shared DNA.

How Would You Define a Half-Fourth Cousin?

A half-fourth cousin is someone who shares only one third great-grandparent with you rather than a pair. This occurs when your common ancestor remarried after a death or divorce, or had children with different partners, creating half-sibling branches in earlier generations.

Half-fourth cousins share approximately half the DNA of full fourth cousins on average, or about 0.1% (7-10 cM). However, the range is wide, and many half-fourth cousins share no detectable DNA at all due to the further dilution of genetic material.

Discovering a half-fourth cousin through DNA testing can provide valuable genealogical clues. If you match someone at the fourth cousin level but the relationship seems unclear, investigating whether your common ancestors had multiple marriages may explain the half-cousin connection. This research often reveals fascinating family stories about widowed ancestors, blended families, or complex marital histories from the 19th century.

Frequently Asked Questions

Is 4th cousin inbreeding?

No, fourth cousins are not considered inbreeding. The genetic distance is too great to pose any meaningful inbreeding risk. With only about 0.2% shared DNA, fourth cousins are genetically similar to unrelated individuals for all practical purposes. Inbreeding concerns typically apply to much closer relationships where shared genetic material exceeds 3%.

Are 4th cousins blood relatives?

Yes, fourth cousins are blood relatives who share common ancestors specifically great-great-great-grandparents (also called third great-grandparents). However, approximately 50% of fourth cousins share no detectable DNA due to the random nature of genetic inheritance over five generations. When DNA is shared, it typically amounts to about 0.2% or 15-20 centimorgans.

Is it okay to have kids with your fourth cousin?

Yes, having children with a fourth cousin is genetically safe. Fourth cousins share minimal DNA (approximately 0.2%), which does not significantly increase the risk of genetic disorders in offspring. All 50 US states allow marriages between fourth cousins, and medical genetics considers this level of relationship to pose no special reproductive concerns. The consanguinity coefficient for fourth cousins is about 0.002, considered negligible in genetic counseling.

How is a fourth cousin related to a second cousin?

Fourth cousins and second cousins are both collateral relatives but differ significantly in generational distance. A second cousin shares great-grandparents (3 generations back), while a fourth cousin shares great-great-great-grandparents (5 generations back). Second cousins typically share about 3.125% of their DNA, while fourth cousins share only about 0.2%. You would likely know many of your second cousins personally, while most fourth cousins remain unknown unless discovered through genealogy research.

Can fourth cousins marry each other?

Yes, fourth cousins can legally marry in all 50 US states and virtually every country worldwide. No jurisdiction restricts marriages at this degree of cousin relationship. The genetic distance is sufficient that marriage laws pose no barriers, and the shared DNA of approximately 0.2% presents no increased risk for offspring compared to unrelated couples.

How can I trace my family tree to find my fourth cousins?

To find fourth cousins, start by identifying your great-great-great-grandparents (third great-grandparents) in your family tree. Research their children beyond your direct ancestor line, then trace each sibling’s descendants forward to the present day. DNA testing through AncestryDNA, 23andMe, or MyHeritage can also identify fourth cousin matches automatically. Building a robust family tree with accurate documentation helps confirm these distant relationships when DNA matches appear.

What is the difference between a fourth cousin and a fourth cousin once removed genetically?

Genetically, fourth cousins once removed share less DNA than true fourth cousins due to the additional generational gap. True fourth cousins share approximately 0.2% or 15-20 centimorgans. Fourth cousins once removed (either your parent’s fourth cousin or your fourth cousin’s child) typically share about 0.1% or 10-15 centimorgans. Both relationships are at the edge of DNA detection, meaning many such relatives share no measurable DNA at all.

Are fourth cousins blood related?

Fourth cousins are indeed blood related, sharing common ancestors specifically their third great-grandparents (great-great-great-grandparents). They possess a minimal amount of shared DNA, typically around 0.2% or 15-20 centimorgans when detectable. However, approximately half of all fourth cousin pairs share no DNA that current testing can identify due to the random nature of genetic recombination across five generations.

Conclusion

Fourth cousins represent a fascinating bridge between your documented family history and the vast network of genetic relatives that DNA testing has revealed. Sharing great-great-great-grandparents from approximately five generations ago, these distant relatives connect you to ancestors who lived in a world dramatically different from our own.

The genetic reality of fourth cousin relationships is striking: while you share about 0.2% of your DNA (15-20 centimorgans) with those fourth cousins where a genetic connection survives, approximately half of all fourth cousin pairs share no detectable DNA at all. This randomness makes each confirmed fourth cousin match a small genealogical miracle worth investigating.

With an average of 1,570 fourth cousins per person, these relationships form the outer edges of your family network. They are legally eligible marriage partners, pose no genetic concerns for offspring, and increasingly serve as valuable collaborators in genealogy research. Whether you discover them through traditional research or DNA matching, fourth cousins offer windows into family stories that might otherwise remain forever hidden.

Understanding what a fourth cousin is helps you make sense of your DNA results, appreciate the complexity of your family tree, and recognize that family extends far beyond the relatives you grew up knowing. In a world of billions, discovering even one fourth cousin creates a tangible link across centuries of human history.