Going from Catalan to Occitan (Occitan) has a composite linguistic distance of 13% (curated lexical data). Below is the dimension-by-dimension breakdown.
Shared vocabulary, cognates, and loanwords.
Morphology, syntax, word order, cases.
Shared sounds and phoneme inventory.
Latin → Latin
Indo-European ↔ Indo-European
The 5 languages with the lowest linguistic distance from Catalan:
A quick 3-question check between Catalan and Occitan. No signup.