The degrees of consanguinity between two people are counted, in almost every U.S. legal setting, by adding up the generational steps that separate them through their nearest common ancestor. One step equals one degree. Your parent is one degree away, your grandparent two, your sibling two, your uncle three, and your first cousin four. That number decides real things: who inherits when there’s no will, who you can legally marry, who counts as a “relative” for federal nepotism rules, and who can make medical decisions for you if you can’t.
The Counting Method That Actually Applies
Two historical systems for counting degrees survive, and they produce different numbers for the same relationship. The civil law method, rooted in Roman law, counts every generational step between two people through their nearest common ancestor. It is the method used by nearly every U.S. state court and statute. The canon law method, developed by the Catholic Church for marriage regulations, counts only the longer of the two lines back to the common ancestor and produces smaller numbers (first cousins are second degree under canon law, fourth degree under civil law).
Unless you are working with Catholic Church marriage rules, civil law is the count that applies to you. Every example in this article uses it.
Counting a Direct-Line Relationship
Lineal consanguinity covers people in your direct line of descent, either up or down. Parents, grandparents, and great-grandparents form the ascending line. Children, grandchildren, and great-grandchildren form the descending line. Each generation is one degree, with no detours.
- Parent and child: first degree
- Grandparent and grandchild: second degree
- Great-grandparent and great-grandchild: third degree
Courts treat lineal kinship as the strongest form of blood relationship because the connection runs in a straight, unbroken line. In virtually every state, lineal descendants get first priority when an estate is divided without a will.
Counting a Side-Branch Relationship
Collateral relatives share a common ancestor but do not descend from one another. Siblings, aunts and uncles, nieces and nephews, and cousins all fit here. Counting them takes a two-part trip: up to the shared ancestor, then back down to the other person. The common relationships work out like this:
- Siblings: up one step to the shared parent, down one step. Second degree.
- Niece or nephew: up one to your parent, down two to your sibling’s child. Third degree.
- Aunt or uncle: up one to your parent, up one to your grandparent, down one to your parent’s sibling. Third degree.
- First cousins: up two to the shared grandparent, down two. Fourth degree.
- First cousins once removed: up two, down three (or the reverse). Fifth degree.
- Second cousins: up three to the shared great-grandparent, down three. Sixth degree.
The Step-by-Step Procedure
For any two people, the count works the same way. Identify the two people. Find their nearest common ancestor (the closest person from whom both descend). Then:
- Starting from the first person, count each generation upward to the common ancestor. Each generation is one degree.
- From the common ancestor, count each generation downward to the second person.
- Add the two numbers. The total is the degree of consanguinity.
To find the degree between you and your uncle: up to your parent (one), up to your grandparent (two), down to your uncle (three). Third degree. A visual family tree with each generation on its own horizontal row cuts down on mistakes once you get past cousins and into “removed” territory.
Blood vs. Marriage, and Two Wrinkles Worth Knowing
Consanguinity means blood relationship. Affinity is the relationship created by marriage. Your spouse’s parents and siblings become your relatives by affinity, never your consanguineous relatives. Stepchildren and stepparents are affinity relationships too, which is why stepchildren generally don’t inherit under intestate succession unless they’ve been legally adopted. When a statute or court form asks about “degrees of consanguinity,” it means blood only. Some statutes say “consanguinity or affinity” when they intend to cover both, so read the wording carefully.
Adopted children are treated as first-degree lineal relatives of their adoptive parents for inheritance purposes in every state, and legal adoption generally severs inheritance rights from the biological parents. A common exception: when a stepparent adopts, many states preserve the child’s right to inherit from the biological parent married to the stepparent.
Half-blood siblings share one parent rather than two. The Uniform Probate Code, adopted in some form by roughly half the states, treats half-blood the same as whole-blood for inheritance. Other states don’t. Florida gives half-blood relatives half the share of whole-blood relatives; Rhode Island treats them equally. If a half-blood relationship matters to your situation, check your state’s rule.
Where the Degree Number Matters
Intestate Inheritance
When someone dies without a will, state intestacy law distributes the estate by degrees of consanguinity. Surviving spouse first, then children (first degree), then parents (first degree ascending), then siblings (second degree), then nieces and nephews (third degree), and outward from there. The Uniform Probate Code caps intestate inheritance at descendants of the deceased’s grandparents; more distant relatives are cut off, and if no closer kin exist the estate passes to the state. About half of U.S. states allow unlimited collateral succession, so very distant relatives can still inherit. Others stop at the fifth degree or use a “parentelic” system tied to a specific ancestor. Which side of that line your state falls on can decide whether a distant cousin inherits or the government does.
Marriage
Every state prohibits marriage between lineal relatives and between siblings, regardless of degree. The rules split at first cousins (fourth degree): roughly half of states ban first-cousin marriages, and a handful allow them, sometimes with conditions like age minimums or genetic counseling. Second-cousin marriages (sixth degree) are legal everywhere. States typically define prohibited relationships using consanguinity charts running to the fourth or fifth degree.
Federal Nepotism
Federal law bars government officials from hiring, promoting, or advocating for the advancement of their relatives within the agency they serve or control. The statute defines “relative” broadly, covering parents, children, siblings, uncles, aunts, first cousins, nephews, nieces, spouses, in-laws, step-relatives, and half-siblings.1Office of the Law Revision Counsel. United States Code Title 5 – 3110 Employment of Relatives Restrictions That reaches roughly to the third degree of consanguinity and captures several affinity relationships. State and local governments have their own nepotism rules with varying definitions.
Tax Rules
The IRS uses kinship in several places, and the definition changes with the provision. For related-party rules that block deducting losses on sales between family members, “family” includes siblings (whole or half blood), a spouse, ancestors, and lineal descendants.2Office of the Law Revision Counsel. United States Code Title 26 – 267 Losses Expenses and Interest With Respect to Transactions Between Related Taxpayers For private foundation rules, the definition is narrower: spouse, ancestors, children, grandchildren, great-grandchildren, and the spouses of those descendants, and it explicitly excludes siblings.3Internal Revenue Service. Member of the Family Which relatives count depends on the specific statute in play.
Medical Decision-Making
If you become incapacitated without a healthcare proxy in place, state law names who can decide for you. The priority list varies but tracks consanguinity closely: spouse, then adult children, then parents, then siblings. Some states extend to grandchildren, grandparents, aunts and uncles, or close friends. Signing a healthcare power of attorney is how you avoid relying on the default order.
Proving the Chain
To establish a degree of consanguinity in court, you need documentation linking each person along the chain. Birth certificates are the strongest evidence because they establish parent-child relationships directly. Marriage certificates connect surnames and confirm spousal links that produced children. Death certificates can fill gaps when older relatives are gone and their birth records are incomplete. For earlier generations, church baptismal records, family bibles, census records, and immigration documents can serve as secondary evidence. Laying it all out as a family tree with one generation per horizontal row makes the count easy to check and gives a court or attorney a clear picture of the relationship you’re claiming.