In 1975 -- by no coincidence the first year that benefits were indexed to inflation -- Social Security's pension fund, whose formal title is Old-Age and Survivors Insurace (OASI), paid out more than it took in.

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Accordingly, a private replacement for Social Security would have to take the form of a fully-inflation-indexed annuity with zero risk of default.

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The thresholds beyond which first 50 percent and then 85 percent of your Social Security benefits are subject to federal income taxation are explicitly NOT indexed for inflation.

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