How to read the band →
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).
Isaias
Isaias has been climbing in recent years. All-time it's been given to 18,644 U.S. babies, the 845th most common name by sound today, peaking at 755 in 2025, with 755 in 2025.
Isaias has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).