Measures of complex functional decision-making capacity can greatly aid in assessing mild cognitive impairment (MCI) and facilitating early intervention in dementia care. We examined the ability of the Assessment of Functional Capacity Interview (AFCI) to detect functional differences among older adults who were cognitively unimpaired (CU), or who presented with subjective cognitive decline (SCD) or MCI. A sample of 97 older adults (CU; n = 30, Mage = 74.64 ± 7.42 years; SCD; n = 34, Mage = 72.56 ± 6.43 years; MCI; n = 33, Mage = 78.28 ± 7.55 years) underwent neuropsychological testing and responded to the Financial Capacity Instrument (FCI-SF). Informants completed the Assessment of Functional Capacity (AFCI), an instrument of functional decision-making capacity, and responded to the Social Vulnerability Scale (SVS15) and Amsterdam Instrumental Activity of Daily Living (A-IADL-Q-SV), a measure of functional status, for comparison. According to informant-reported responses, the CU group had significantly lower AFCI total (and domain) scores, (2) = 27.59, <.001, relative to MCI. Additionally, the CU group had significantly lower AFCI scores in the domain relative to the SCD group, (2) = 14.06, <.05. In the overall sample, AFCI total scores were associated with FCI-SF, SVS15, and A-IADL-Q-SV scores and cognitive measures. Our results demonstrate that the AFCI is sensitive to impairment in safety, social, financial, and medical functioning in MCI and is associated with measures of cognitive functioning and social vulnerability in older adults. Incorporating this instrument as a supplement to cognitive screening instruments may aid in the prevention of hazardous decision-making in older adults.