Going from Dutch to Icelandic (Íslenska) has a composite linguistic distance of 49% (heuristic estimate). 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 Dutch:
A quick 3-question check between Dutch and Icelandic. No signup.