Theory is a distinctive girls' name in United States, ranking #13675 in 2018 with 7 recorded births. This places Theory in the bottom 25% 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 2018, approximately 1 in every 242,918 girls born was named Theory. STABLE Recent data shows the name is currently stable.