The ability to predict future decline in cognitive systems using the cerebrospinal fluid (CSF) biomarkers 42 amino acid form of amyloid-β (Aβ42) and total tau (T-tau) is not fully understood. In a clinical sample ranging from cognitively healthy to dementia (n = 326), linear regression models were performed in order to investigate the ability of CSF biomarkers to predict cognitive decline in all cognitive domains from baseline to 2-year follow-up. Gender, age, and years of education were included as covariates. In patients with subjective cognitive impairment, T-tau had a small impact on executive functions (r2 = 0.07). T-tau had a small to moderate influence (r2 = 0.06-0.11) on all cognitive functions with the exception of visuospatial functions in patients with mild cognitive impairment (MCI). In patients with dementia, the impact of T-tau was large (r2 = 0.29) on semantic memory. Aβ42 had a small effect (r2 = 0.07) on speed and executive functions in MCI. In patients with dementia, Aβ42 had a moderate influence (r2 = 0.13-0.24) on semantic and verbal working memory/fluency. Our results speak in favor of the notion that CSF biomarkers reflect the rate of cognitive decline across the continuum of cognitive impairment from healthy to dementia. CSF predicted subsequent decline in more cognitive domains among MCI cases, but the impact was most pronounced in patients with dementia.