Degree of Kinship: Definition, Calculation, and U.S. Legal U...

Introduction

The degree of kinship measures how closely two people are related by blood. In U.S. law, this measurement affects who inherits when there’s no will, who may be considered first in certain custody or guardianship matters, when a judge or official must step aside because of a conflict, and which marriages are prohibited. Put simply, it’s a count of the steps between two relatives through their nearest common ancestor, with one degree for each step.

This guide explains what the degree of kinship means, how to calculate it, where it applies in American law, and what to watch for with adoption, half-blood, and step relationships.

What You’ll Learn

• What “degree of kinship” means and how it differs from relationships by marriage (affinity)
• How to calculate degrees using the widely used civil-law method
• Typical degrees for common relatives (siblings, aunts/uncles, cousins)
• Where degrees of kinship matter in the U.S.: intestate succession, custody, marriage/incest rules, conflicts, nepotism, and jury/judge rules
• How adoption, step-relatives, and half-blood relatives are treated
• Practical steps to document kinship with family trees and charts
• State-to-state differences you should check before relying on a specific rule

Core Concepts

Consanguinity vs. Affinity: Who Counts as a Relative?

• Consanguinity (degree of kinship) refers to blood relationships: parent-child, siblings, grandparents, aunts/uncles, cousins, and so on.
• Affinity refers to relationships created by marriage: spouse, in-laws, step-relatives. These are not blood ties, though many state laws treat them alongside blood relatives for ethics and nepotism rules.
• Adoption: In most U.S. contexts, an adopted child is treated the same as a biological child for inheritance and family status. A full adoption generally ends the legal parent-child relationship with the birth parents (stepparent adoptions are a common exception).
• Step-relatives: Stepparents and stepchildren usually are not considered related by consanguinity. Their legal status depends on specific statutes.
• Assisted reproduction: Donors are typically not legal parents by statute or court order. Legal parentage follows the applicable state laws.

How Degrees Are Counted (Civil-Law Method)

Many American statutes and policies use the civil-law method to count kinship degrees:

1. Identify the nearest common ancestor shared by the two people.
2. Count one step (one degree) for each generation up from Person A to the common ancestor.
3. Add one step for each generation down from that ancestor to Person B.
4. The total is the degree of kinship.

Examples using the civil-law method:

• Parent ↔ Child: 1st degree
• Grandparent ↔ Grandchild: 2nd degree
• Siblings: 2nd degree (A up to parent = 1; down to sibling = 1; total = 2)
• Aunt/Uncle ↔ Niece/Nephew: 3rd degree (A up to parent = 1; up to grandparent = 2; down to aunt/uncle = 3)
• First Cousins: 4th degree (A up to parent = 1; up to grandparent = 2; down to aunt/uncle = 3; down to cousin = 4)
• First Cousin Once Removed: 5th degree (one more generation down or up from the cousin relationship)
• Second Cousins: 6th degree (they share a great-grandparent)

Notes:

• Half-siblings are still 2nd-degree relatives. The degree counts steps, not the number of shared parents. Many states (including those following the Uniform Probate Code) give half-blood and whole-blood relatives the same share in intestacy.
• “Removed” indicates a difference in generations between cousins (for example, your cousin’s child is your first cousin once removed).

Common Relationships and Their Degrees

Quick reference list (civil-law method):

• 1st degree: Parent, child
• 2nd degree: Sibling, grandparent, grandchild
• 3rd degree: Aunt/uncle, niece/nephew, great-grandparent, great-grandchild
• 4th degree: First cousin, great-aunt/uncle, great-niece/nephew
• 5th degree: First cousin once removed
• 6th degree: Second cousin

Remember: Step-relatives are not blood relatives. Affinity (in-laws) is often counted separately when a statute mentions relatives “by affinity.”

Other Systems You May See in U.S. Law

• Parentelic system (common in modern intestacy statutes, including the Uniform Probate Code): Distributes estates by family “branches” (descendants first; if none, then parents and their descendants; then grandparents and their descendants, etc.). Degree-of-relationship may be used to break ties among relatives within the same branch.
• Canon-law method (historical): Counts only to the more distant common ancestor line. It appears less often in modern U.S. statutes but you may see references in older sources.
• Practical takeaway: Always check the specific state statute. For inheritance, many states use parentelic rules, while conflict, ethics, and nepotism provisions often reference degrees of consanguinity (frequently up to the third degree).

Using Family Trees and Kinship Charts

• Family trees (pedigrees) show each generation, which makes counting steps straightforward.
• Consanguinity charts (kinship charts or genograms) use standardized symbols and lines to show the steps up to a common ancestor and down to a relative. They are useful exhibits in probate filings and custody or guardianship cases.

Key Examples or Case Studies

Estate of Jackson (probate, intestate succession)

• Context: A decedent died without a will. The court had to determine the nearest next of kin to inherit.
• What the court looked at: Each claimant’s degree of kinship, often combined with the state’s parentelic rules.
• Outcome reported: The estate passed to the decedent’s children and grandchildren as the relatives in the closest degree under the controlling statute.
• Key point: When there is no will, the order of heirs is usually driven by statute. Degree of kinship helps the court rank relatives within or across family branches if the statute calls for it.

Smith v. Smith (custody among relatives)

• Context: A custody dispute among grandparents, aunts, and uncles.
• What the court looked at: The closeness of the family relationship alongside the best-interest-of-the-child standard (the governing standard in U.S. custody cases).
• Outcome reported: Custody was awarded to the grandparents, who were closer in degree to the child than the aunts and uncles.
• Key point: Degree of kinship can support a custody placement, but it is only one factor. Courts must prioritize the child’s best interests.

Judicial or Official Conflicts (recusal and nepotism)

• Context: A judge, juror, or public official has a relationship to a party or applicant.
• What the rules look at: Whether the person is related within a specified degree (often the third degree) by blood or marriage.
• Typical result: The judge recuses, the juror is excused for cause, or the official is barred from hiring or appointing the relative.
• Key point: Degrees of kinship provide a bright-line test for conflicts and ethics compliance.

Practical Applications

• Count degrees accurately:

  • Identify the nearest common ancestor.
  • Count one step per generation up from Person A to the common ancestor.
  • Count one step per generation down to Person B.
  • Add the steps.

• Use the right system for the task:

  • Probate and intestacy: Many states follow parentelic distribution first. Degree-of-relationship may break ties among collateral relatives of the same branch if the statute says so.
  • Conflicts, recusal, and nepotism: Statutes and rules often specify “within the third degree” (or another number), including both consanguinity and affinity.
  • Marriage and incest rules: States list prohibited degrees (for example, marriage to a sibling is prohibited; marriage to a first cousin may be allowed or prohibited depending on the state).

• Document family relationships:

  • Build a family tree and, if needed, a consanguinity chart. Label each step in the chain to show the degree.
  • Keep records: birth certificates, adoption decrees, marriage certificates, paternity orders, and court judgments establishing parentage.

• Address special situations:

  • Adoption: Treat adoptive parent-child as a 1st-degree relationship for most purposes; confirm how your state treats connections to birth relatives after adoption.
  • Half-blood: In many states (including those that use the Uniform Probate Code), relatives of the half blood take the same share as whole blood.
  • Step-relatives: Unless a statute says otherwise, step-relatives are not blood relatives and usually do not inherit as next of kin.
  • Assisted reproduction: Follow state parentage laws and court orders to determine legal parent-child relationships.

• Common use cases:

  • Probate filings: Show how close each claimant is and cite the statute that applies.
  • Custody/guardianship: Present the family tree and the relative’s degree alongside the child’s best-interest factors.
  • Judicial recusal and juror challenges: Quickly identify if a relation falls within the prohibited degree.
  • HR and ethics compliance: For public agencies and some private employers, verify whether an applicant is related within a prohibited degree for hiring.

• Immigration note:

  • U.S. immigration law sets specific family categories (e.g., spouse, parent, child, sibling) rather than using a numeric degree for eligibility. Still, clear documentation of the family relationship is essential in petitions.

Summary Checklist

• Know the difference between consanguinity (blood) and affinity (marriage).
• Use the civil-law method: one step per generation up to a common ancestor and down to the other relative.
• Remember common degrees: parent/child (1), siblings (2), aunt/uncle or niece/nephew (3), first cousins (4).
• Confirm state rules: Many use parentelic systems for intestacy; others reference degrees directly.
• Treat adoption as creating full parent-child ties unless your state provides an exception.
• Half-blood usually equals whole-blood in modern intestacy statutes.
• Step-relatives are not blood relatives unless a statute extends coverage.
• For conflicts and ethics, check the exact degree in the rule (often third degree).
• Use family trees and consanguinity charts to present clear, step-by-step counts.
• When in doubt, cite the applicable state statute or rule and attach documentation.

Quick Reference