Theory is a distinctive girls' name in United States, ranking #12043 in 2020 with 8 recorded births. This places Theory in the bottom 31% of ranked US girls' names for the year. Its actual usage is classified as Rare. The name reached its all-time peak in 2025 with 20 births ranking #6092. In 2020, approximately 1 in every 201,939 girls born was named Theory. STABLE Recent data shows the name is currently stable.