Solid line = floor (spellings that unambiguously belong to the group). Shaded band up to the dashed edge = ceiling (the most it could reach if every ambiguous spelling counted here).
Kieran has been climbing in recent years. All-time it's been given to 24,259 U.S. babies, the 744th most common name by sound today, peaking at 1,000 in 2025, with 1,000 in 2025.
By sound, Kieran also includes the spellings Kiran. Spellings sometimes heard the same way: Kyren, Kyran.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).