How Old Is the Court?

Service starts at the judicial oath, not the commission. The two differ for a quarter of the Court, sometimes by months — Earl Warren took the oath in October 1953 under a recess appointment and was not commissioned until March 1954. The Court states the rule itself: until the oath is taken, a member “is not vested with the prerogatives of the office.”

Service ends when a justice leaves the bench, not when they die. This is the one that quietly ruins the arithmetic. The Federal Judicial Center does not treat retirement as the end of judicial service: for Stanley Reed it records senior status in February 1957 and “service terminated” in April 1980, twenty-three years apart. Reed stopped being a member of this Court in 1957. 38 of the 116 justices left that way, and using the other date would leave a dozen dead men on the bench at any given moment.

A promotion is not a new tenure. Edward White, Harlan Fiske Stone and William Rehnquist each appear in the federal record as two appointments, the associate justiceship ending the same day the Chief Justice’s oath is taken; here they are one continuous span. Charles Evans Hughes is the exception and is kept as two: he resigned in 1916 to run for President and came back as Chief Justice fourteen years later.

Four birth dates are not known to the day. John Blair, James Wayne and John Catron are recorded only by year, John Rutledge only by month. Each is estimated to the midpoint. Re-running the whole series with those four births pinned first to the earliest and then to the latest day they could be moves the line by at most 0.308 of a year, and that worst case falls in the 1860s, when Catron and Wayne were both still sitting. It is about a third of a year — larger than the chart’s rounding, and stated here rather than buried. The one thing it could plausibly touch is the order of the third and fourth steepest falls below, which are 0.039 of a year apart.

The average is over justices, not over seats. A day with a vacancy divides by the justices actually in office, so an empty seat neither ages nor rejuvenates the Court, and the seats-filled column in the table is where that shows. The thinnest bench on record: in 1835 an average day found only 5.5 justices in office — Duvall resigned that January and Marshall died that July, and neither chair was filled until 1836.

Every date was checked against the Federal Judicial Center’s Biographical Directory of Article III Federal Judges, one justice at a time. The site’s birth and death dates agreed with the federal record in 115 of 116 cases; the exception is John Rutledge, where the Center gives 21 June 1800 and the South Carolina Encyclopedia, the South Carolina Historical Society, the Supreme Court Historical Society and his own churchyard marker all give 18 July. This page follows the latter. Ages use the mean Gregorian year of 365.2425 days.