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).
Theo
Theo has been climbing in recent years. All-time it's been given to 39,333 U.S. babies, the 177th most common name by sound today, peaking at 4,182 in 2023, with 3,966 in 2025.
Theo has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).