Legal Definitions - certum an et quantum debeatur

The Latin phrase certum an et quantum debeatur translates to "certain whether and how much is owed."

In legal contexts, this principle historically referred to the requirement that, for certain legal actions (such as a defendant claiming that the plaintiff owed them money to offset or reduce the plaintiff's own claim), it had to be absolutely clear and undisputed:

• an: whether a debt exists at all (is there a debt?)
• et quantum debeatur: and exactly how much that debt amounts to (what is the precise amount owed?)

Essentially, before one party could use a debt owed to them by another as a defense or counter-claim, they needed to establish with certainty both the existence of that debt and its exact value.

Here are some examples to illustrate this concept:

• Business Contract Dispute: Imagine Company A sues Company B for non-payment of a large invoice for delivered goods. Company B, in turn, wants to argue that Company A actually owes *them* money due to a separate breach of a service agreement, and they wish to "set off" this amount against Company A's claim. For Company B to successfully use this set-off, they would need to establish certum an et quantum debeatur regarding Company A's alleged debt to them. This means Company B must clearly prove that Company A definitely owes them money (the "an") and provide precise documentation and calculations for the exact amount owed due to the service agreement breach (the "quantum"). If the existence of the breach or the damages are highly disputed and unclear, Company B might struggle to meet this standard.

• Construction Project Counterclaim: A homeowner sues a contractor for failing to complete a renovation project on time and to specification. The contractor wants to counterclaim that the homeowner owes them for several additional tasks that were requested and performed outside the original contract. Before the contractor's counterclaim for these additional tasks can be considered a clear offset against the homeowner's claim, the contractor must demonstrate certum an et quantum debeatur. They need to show clear evidence (e.g., signed change orders, emails, or witness testimony) that the homeowner agreed to pay for the extra work (the "an") and provide precise invoices or cost breakdowns for the exact cost of that work (the "quantum"). If the homeowner disputes ever agreeing to the extra work or the costs are vague, the "certum an et quantum debeatur" standard might not be met.

• Partnership Dissolution: Two partners are dissolving their business, and Partner A claims Partner B owes them a specific sum from an informal loan made years ago to help cover initial startup costs. Partner B, however, denies that a loan ever occurred, claiming it was an investment, or disputes the exact amount and terms. If Partner A wants to use this alleged debt to reduce Partner B's share of the partnership assets during the dissolution, they would need to satisfy certum an et quantum debeatur. Partner A must provide irrefutable proof (e.g., a written agreement, bank statements clearly showing a loan transaction, or consistent financial records) that the loan was indeed made (the "an") and precisely calculate the outstanding balance, including any agreed-upon interest (the "quantum"). Without such clarity and certainty, the alleged debt cannot be treated as a definite offset.