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).
Kristen was more common in the past and has since settled at a lower, steady level. All-time it's been given to 457,190 U.S. babies, the 1,683rd most common name by sound today, peaking at 20,722 in 1982, with 177 in 2025.
By sound, Kristen also includes the spellings Kristin, Christen, Christin, Kristyn, Kristan, Cristin, Krysten, Krystin, Cristen.