Background: Little is known about within-person frailty index (FI) changes during the last years of life. In this study, we assess whether there is a phase of accelerated health deficit accumulation (terminal health decline) in late-life. Material and methods: A total of 23,393 observations from up to the last 21 years of life of 5713 deceased participants of the AHEAD cohort in the Health and Retirement Study were assessed. A FI with 32 health deficits was calculated for up to 10 successive biannual, self- and proxy-reported assessments (1995–2014), and FI changes according to time-to-death were analyzed with a piecewise linear mixed model with random change points. Results: The average normal (preterminal) health deficit accumulation rate was 0.01 per year, which increased to 0.05 per year at approximately 3 years before death. Terminal decline began earlier in women and was steeper among men. The accelerated (terminal) rate of health deficit accumulation began at a FI-value of 0.29 in the total sample, 0.27 for men, and 0.30 for women. Conclusion: We found evidence for an observable terminal health decline in the FI following declining physiological reserves and failing repair mechanisms. Our results suggest a conceptually meaningful cut-off value for the continuous FI around 0.30.