The degrees of affinity are the numbered steps used to measure how closely you are related to your spouse’s blood relatives, and the count determines whether a given in-law or step-relative falls inside laws on nepotism, judicial recusal, dependency claims, and other rules that treat marriage-based kin as family. First degree covers your spouse’s parents and children; second degree covers your spouse’s siblings, grandparents, and grandchildren; third degree reaches your spouse’s aunts, uncles, nieces, and nephews. Each step away from your spouse adds one degree.
Affinity Versus Consanguinity
Legal kinship comes in two forms. Consanguinity links people who share a biological ancestor: siblings, parents, cousins. Affinity links you to your spouse’s blood relatives, which is how the law describes in-laws and step-relatives. The distinction is not decorative. Statutes on hiring, recusal, inheritance, and benefits often treat these two kinds of kinship differently, so getting the category right is the first step to applying any rule.
Affinity starts the moment a marriage is legally valid. No separate paperwork establishes the tie to your new in-laws; the marriage certificate does it. From that point your spouse’s parents, siblings, and children are your relatives by affinity for legal purposes. Stepchildren work the same way. If your spouse has children from a prior relationship, they become your stepchildren by affinity as soon as the marriage takes effect.
How To Count Degrees of Affinity
Federal law and most states use the civil law counting method, which 28 U.S.C. § 455 adopts expressly for federal proceedings.1Office of the Law Revision Counsel. 28 USC 455 – Disqualification of Justice, Judge, or Magistrate Judge The method is simple. Start at your spouse. Count the steps up to a common ancestor and back down to the relative. That total is the degree.
First degree: your spouse’s parents (your in-laws) and your spouse’s children (your stepchildren). Some formulations also count your spouse as first degree.
Second degree: your spouse’s siblings, your spouse’s grandparents, and your spouse’s grandchildren. Sisters- and brothers-in-law sit here.
Third degree: your spouse’s aunts, uncles, nieces, nephews, and great-grandparents.
The count is not academic. When a statute restricts hiring “within the second degree of affinity,” first- and second-degree relatives are covered and third-degree relatives are not. When a recusal rule reaches the third degree, it sweeps in a much wider circle. Miscounting can turn a lawful hire into a violation or a proper case assignment into grounds for reversal.
Does Affinity End at Divorce?
The honest answer is: it depends on which law you are asking about. For most state law purposes, affinity ends with the marriage. Once divorced, your former mother-in-law is generally no longer your relative by affinity.
Federal tax law goes the other way. The IRS treats relationships created by marriage as permanent, so they continue after divorce and after the death of the spouse who created the tie. A former daughter-in-law can still be claimed as a dependent years after the divorce if she meets the qualifying-relative tests.2Internal Revenue Service. Publication 501 (2025), Dependents, Standard Deduction, and Filing Information
Some state nepotism statutes also keep affinity intact after divorce when children were born of the marriage, on the theory that the family link is still real. Check the specific statute before assuming the connection has dissolved.
Federal Anti-Nepotism Law
Under 5 U.S.C. § 3110, no federal official may appoint, employ, promote, or advocate for the hiring of a relative in the agency they oversee. The statute’s definition of “relative” names in-laws (father-in-law, mother-in-law, son-in-law, daughter-in-law, brother-in-law, sister-in-law) alongside stepparents, stepchildren, stepsiblings, and half-siblings.3Office of the Law Revision Counsel. 5 USC 3110 – Employment of Relatives; Restrictions
The consequence is aimed at the hire, not the official. The Treasury cannot pay a person appointed in violation of the statute, so the appointment is effectively unenforceable and work already performed may go uncompensated.3Office of the Law Revision Counsel. 5 USC 3110 – Employment of Relatives; Restrictions
State Nepotism Rules
Roughly half the states have their own anti-nepotism statutes, and the degree cutoffs vary. Some stop at the second degree of affinity, covering in-laws and stepchildren but not siblings-in-law’s spouses or more distant marriage-based kin. Others extend to the third or fourth degree, reaching a much wider circle.
Penalties vary too. A violation may be grounds for removal from office, a misdemeanor, forfeiture of the position, or a fine. Anyone in public employment should look up the exact state statute rather than working from a general assumption about what’s prohibited.
Private employers are not bound by these government nepotism rules. Many large companies do adopt policies that mirror them, typically requiring disclosure of affinity relationships during hiring, with termination as the consequence for failing to disclose.
Judicial Recusal Reaches the Third Degree
Federal judges must disqualify themselves from any case involving a person within the third degree of relationship to the judge or the judge’s spouse. Under 28 U.S.C. § 455, recusal is required if such a relative is a party, a lawyer in the case, a material witness, or someone with a financial interest that could be substantially affected by the outcome.1Office of the Law Revision Counsel. 28 USC 455 – Disqualification of Justice, Judge, or Magistrate Judge
The third-degree threshold reaches farther than most people expect. It covers not just a judge’s in-laws but the spouse’s aunts, uncles, nieces, and nephews. If a judge’s spouse’s nephew appears as counsel, the judge must step aside. The ABA Model Code of Judicial Conduct uses the same third-degree standard and extends it to domestic partners as well as legal spouses.4American Bar Association. Rule 2.11: Disqualification
Claiming In-Laws and Step-Relatives on Your Taxes
The IRS lets you claim certain relatives by affinity as dependents if they meet the qualifying-relative tests. In-laws and step-relatives get an advantage over unrelated household members: they do not have to live with you to qualify. A mother-in-law in her own apartment can still be your dependent if the financial tests are met.2Internal Revenue Service. Publication 501 (2025), Dependents, Standard Deduction, and Filing Information
Four conditions have to line up:
- The person is not a qualifying child of you or anyone else.
- The person is on the IRS’s list of relationships (which includes in-laws and step-relatives) or, if not, lived with you all year.
- The person’s gross income is under $5,200 for the year, per the most recent IRS guidance.
- You provided more than half of the person’s total support for the year.
And, again, these affinity ties do not end when the marriage does for tax purposes. A former daughter-in-law can still qualify years after the divorce.2Internal Revenue Service. Publication 501 (2025), Dependents, Standard Deduction, and Filing Information
Social Security Benefits for Stepchildren
A stepchild can draw Social Security on a step-parent’s record, but the affinity relationship has to have lasted long enough. If the step-parent is living, the child must have been a stepchild for at least one year before applying. For survivor benefits after a step-parent’s death, the stepchild must have held that status for at least nine months before the death.5Social Security Administration. Stepchild-Stepparent Relationship
The nine-month rule has exceptions. It can be waived when the step-parent’s death was accidental or occurred in the line of military duty. It also does not apply where the step-parent and the child’s biological parent had been previously married, divorced, and remarried, provided the nine-month threshold was already met during the earlier marriage.5Social Security Administration. Stepchild-Stepparent Relationship
Marriage Restrictions Between Relatives by Affinity
Every state prohibits marriage between close blood relatives. Restrictions on marrying someone related only by affinity are less uniform. Some states bar marriages between a stepparent and stepchild, treating the family relationship as close enough to warrant a prohibition. Others allow the marriage, particularly after the death of the spouse who created the connection.
Where the prohibition exists, a marriage entered in violation of it can be declared void from the start (void ab initio), and some jurisdictions attach criminal penalties, though enforcement is rare. Check the state family code before applying for a license if the potential spouse is a former step-relative.
Inheritance and Stepchildren
Stepchildren occupy an awkward place in probate. In most states, when a step-parent dies without a will, stepchildren have no automatic right to inherit. Intestate succession statutes generally follow blood lines, moving through biological children, parents, siblings, and more distant blood relatives before reaching anyone connected only through marriage.
Exceptions are limited. Some states let stepchildren inherit if no blood relatives can be located, to keep the estate from escheating. A few give stepchildren priority under narrow conditions, such as when the biological parent who created the step-relationship predeceased the step-parent within a defined window.
The doctrine of equitable adoption offers another route. If a step-parent promised or agreed to adopt a stepchild but never completed the legal process, some courts will treat the child as an adopted heir. The stepchild has to prove the intent to adopt by clear and convincing evidence, which is a higher bar than most probate matters use.6Social Security Administration. Equitable Adoption – General
The reliable way to leave property to a stepchild is to name the stepchild in a will or trust. Waiting on intestate succession or equitable adoption is a gamble, and the legal fight when it comes tends to eat into whatever is left of the estate.