The Celtic Index measures how closely your DNA matches a set of ancient Celtic samples from peer-reviewed studies, based on genetic distance. It's a specific comparison to ancient individuals.
Modern ancestry reports (like our Deep Ancestry or AncestryDNA) work differently — they focus on your recent genetic heritage, usually going back around 10 generations, using current reference populations and different algorithms. Because the methods and reference datasets are so different, the percentages won't line up directly. They're two different lenses on the same DNA, and together they give you a fuller picture.