Definition
Latin: "the day from which." Dies a quo designates the starting point of a legal period — the day from which a transaction, limitation period, or computation of time begins to run. Its counterpart is dies ad quem, the day to which, marking the endpoint or conclusion of the same period. Together, the two terms define the outer boundaries of any legally significant span of time.
The phrase is encountered principally in the computation of limitations periods, prescription, notice deadlines, and contractual or transactional durations. Whether the dies a quo itself is counted within the period, or whether counting begins the following day, has been a recurring question of procedural and substantive law resolved differently across jurisdictions and time periods.
Common Confusion
Dies a quo and dies ad quem are frequently cited as a matched pair, and researchers sometimes invert or misremember which is the starting point and which is the endpoint. The mnemonic is embedded in the Latin: a quo means "from which" (origin); ad quem means "to which" (destination). Neither term should be confused with dies amoris — a separate Latin legal phrase meaning "the day of love," referring historically to the fourth day (quarto die post) of a term, granted by the court's favor as the defendant's appearance day. Rapalje & Lawrence's entry places dies amoris immediately after dies a quo, a proximity in the sources that has occasionally caused confusion in research.
Why It Matters in Research
The practical significance of dies a quo turns almost entirely on one question: is the first day counted or excluded? Common law courts historically excluded the dies a quo from the computation, beginning the count on the day after the triggering event. Civil law systems applied similar principles but with important variations. Many modern procedural codes codify the rule explicitly, but historical sources — including treatises and early cases applying limitations statutes — often left the question to inference or relied on the civil law background meaning. Researchers working with pre-codification materials must be alert to this ambiguity.
The term appears most frequently in historical legal writing, treatises on limitations and prescription, and civil law-inflected materials. In modern American practice, the Latin phrase itself is rarely used in statutes or judicial opinions; practitioners instead speak of accrual dates, trigger events, or commencement dates. When a modern court or statute uses "accrual" language, it is typically addressing the same concept the older sources called dies a quo. Researchers tracing the development of limitations doctrine should expect to shift vocabulary as sources move from nineteenth-century treatise language into twentieth-century statutory and case law.
Because dies a quo is definitionally linked to dies ad quem, the two terms should be researched together. Treatise discussions of one virtually always treat the other, and any corpus entry or case involving period computation may use either or both.
Historical Dictionary Support
Black's, Rapalje & Lawrence, and Burrill are in close agreement on the core meaning: dies a quo is the starting day of a transaction or period, dies ad quem is the ending day. All three sources cite or reference Mackeldey's Roman Law as authority, reflecting the term's civilian provenance. Burrill cites Mackeldey directly at volume 1, section 172; Black's references the same source at section 185. The slight variation in section numbers between editions of Mackeldey accounts for the discrepancy and is not a substantive disagreement.
Rapalje & Lawrence adds the most practical detail of the three, noting explicitly the role of dies a quo in the computation of periods of time and contrasting it with dies ad quem. Black's adds a note — appearing to be from a later edition — that a dies a quo can also be characterized as "a day of favor," though this gloss is not fully developed and may represent a conflation with the adjacent dies amoris entry. Burrill's treatment is the most spare, providing a clean civil law definition without elaboration. None of the three historical sources addresses the question of whether the dies a quo is itself included in or excluded from the period being measured, which is precisely the operationally significant issue for practitioners and researchers — a gap modern sources must fill.
Jurisdictional Note
Modern American courts and procedural rules generally exclude the dies a quo from period computations, beginning to count the day after the triggering event, but this default rule is frequently modified by statute or rule for specific contexts. Researchers applying this principle to foreign or historical materials should not assume the exclusion rule uniformly applies.