In law, aggregation is the practice of combining separate claims, damages, or coverage amounts into one total figure. It appears most often in civil litigation, where plaintiffs add claims together to meet the dollar threshold for federal diversity jurisdiction, and in insurance, where policyholders combine coverage limits to pay a single loss. The rules governing aggregation in law change depending on how many parties are involved, what kind of interest they share, and whether a case proceeds as an individual lawsuit or a class action.
The Core Distinction Courts Draw
Whether claims can be aggregated usually comes down to the kind of interest the parties hold. A common undivided interest exists when two or more parties share a single legal right that cannot be cleanly split — co-owners of the same property, for example, or employees affected by the same employer policy. Separate and distinct claims involve independent injuries where each person seeks their own recovery.
That distinction controls almost everything that follows. Parties who share a common undivided interest can pool their damages into one amount. Parties with separate and distinct claims generally cannot, and each must independently satisfy any dollar threshold the court imposes.
One Plaintiff, One Defendant
Federal diversity jurisdiction under 28 U.S.C. § 1332 requires the amount in controversy to exceed $75,000, not counting interest and costs.1Office of the Law Revision Counsel. 28 USC 1332 – Diversity of Citizenship; Amount in Controversy; Costs A single plaintiff suing a single defendant may add every claim together to reach that figure, even when the claims are completely unrelated. A $40,000 breach-of-contract claim and a $40,000 personal injury claim against the same defendant combine into an $80,000 total that clears the threshold.
Two limits matter here. First, alternative theories of recovery for the same underlying loss do not stack. If you argue both negligence and strict liability over the same car accident, your amount in controversy is the value of the single loss, not the sum of each theory. A $40,000 car is worth $40,000 regardless of how many legal routes you take to collect for it.
Second, counterclaims the defendant files do not enter the calculation. The statute measures the amount in controversy without regard to any setoff or counterclaim.1Office of the Law Revision Counsel. 28 USC 1332 – Diversity of Citizenship; Amount in Controversy; Costs Only the plaintiff’s claims count.
Punitive damages, by contrast, generally do count. A good-faith demand for $50,000 compensatory and $30,000 punitive against the same defendant produces an $80,000 figure that satisfies the threshold. Courts look at what the plaintiff claims in good faith when the case is filed.
Multiple Plaintiffs
Add a second plaintiff and the rule flips. Two plaintiffs who each suffered $40,000 in independent injuries from the same defendant cannot combine those amounts to claim $80,000 in controversy. Each must independently clear $75,000.
The exception is the common undivided interest. If the plaintiffs jointly own the same property or share a legal right that cannot be easily divided, the full value of that shared interest sets the amount in controversy, not each person’s fractional share. Co-owners suing over the destruction of a single building would ordinarily qualify.
When a case cannot clear the threshold, dismissal from federal court follows, and the plaintiff must refile in state court, which generally has lower or no minimum dollar requirements. A plaintiff whose eventual recovery falls below $75,000 may also be denied costs, or have costs imposed as a penalty.1Office of the Law Revision Counsel. 28 USC 1332 – Diversity of Citizenship; Amount in Controversy; Costs
When Some Plaintiffs Fall Short
Supplemental jurisdiction under 28 U.S.C. § 1367 softens the hard line. A federal court with original jurisdiction over at least one claim may also hear additional related claims from the same case or controversy, even if those additional claims could not stand on their own.2Office of the Law Revision Counsel. 28 USC 1367 – Supplemental Jurisdiction
The Supreme Court applied that principle to extra plaintiffs in Exxon Mobil Corp. v. Allapattah Services. When at least one plaintiff satisfies the $75,000 amount in controversy, other plaintiffs whose claims fall below that figure can still be heard in the same federal proceeding, as long as every claim stems from the same underlying dispute.3Legal Information Institute. Exxon Mobil Corp v Allapattah Services Inc Closely related claims no longer have to be split between federal and state courts.
Class Actions Under CAFA
Class actions follow their own aggregation framework. The Class Action Fairness Act, codified at 28 U.S.C. § 1332(d), explicitly allows claims from all individual class members to be added together to determine the amount in controversy. The combined total must exceed $5,000,000 for CAFA jurisdiction to attach.4Office of the Law Revision Counsel. 28 USC 1332 – Diversity of Citizenship; Amount in Controversy; Costs
CAFA also loosens the diversity requirement. Rather than the complete diversity standard that applies to ordinary diversity cases, class actions need only minimal diversity: at least one class member in a different state from at least one defendant. The class must include at least 100 members.4Office of the Law Revision Counsel. 28 USC 1332 – Diversity of Citizenship; Amount in Controversy; Costs
The practical effect is that claims too small to litigate alone — a $15 overcharge affecting millions of customers, for instance — can reach federal court when the total liability is large enough. CAFA also lets defendants remove qualifying class actions from state to federal court under 28 U.S.C. § 1441.5Office of the Law Revision Counsel. 28 USC 1441 – Removal of Civil Actions
Aggregation in Insurance: Stacking
Aggregation also appears outside litigation, where it is usually called stacking. Stacking lets a policyholder combine coverage limits from more than one source to pay a single loss. It comes up most often with uninsured or underinsured motorist coverage when someone owns multiple vehicles. Two cars on the same policy with $25,000 in coverage each could, with stacking, produce up to $50,000 of available coverage for one accident.
Stacking takes two forms. Intra-policy stacking combines limits for multiple vehicles listed on the same policy. Inter-policy stacking combines coverage from two or more separate policies. Whether either is available depends on your state’s law and the specific language of your policy.
State rules vary widely. Some states prohibit stacking outright, some allow both forms, and others permit only inter-policy stacking. Even where state law allows it, insurers often write anti-stacking clauses into their policies — contract language stating that regardless of the number of vehicles, claims, or premiums, coverage limits will not be added together for the same accident. These clauses are generally enforceable in states that do not require stacking by law, though courts in some states have struck them down as contrary to public policy. The only reliable way to know what applies to you is to read your policy against your state’s rules.