Aim: Home care nurses often use the Resident Assessment Instrument-Home Care (interRAI-HC) to assess health needs. However, this tool does not assess complexity. This study proposes to derive a complexity index (CI) from the interRAI-HC using the operational definition of the dedicated COMID checklist (COmplexité Multidimensionnelle des prises en soins Infirmières à Domicile). Design: Data were collected at the baseline assessment of the fraXity study (N = 231, aged ≥ 65), which relied on an observational longitudinal design. Methods: Measures were the interRAI-HC, from which the CI binary variables were computed and the COMID, used as a reference. Results: Twenty-six CI variables were computed from the interRAI-HC, and all but three correlations were significant. The correlation between the CI score and the COMID score was ρ = 0.730 (p < .001). Conclusions: The study demonstrates that complexity can be assessed directly from the interRAI-HC by deriving a CI.