I am now at my full SS retirement age, but still working. I plan to defer taking SS for two more years. I understand that if my income for those years may increase my SS benefit if they increase the 35-year average. But what if I do a phased retirement, with my last year or two at 75% salary? Those numbers may still be top-35 for my calculation. Will that reduce my SS benefit, or is the calculation "fixed" and safe from reduction once I reach my full SS retirement age?

Hi. You can't reduce your monthly benefit rate by continuing to work, be it part-time or full-time. If your earnings in future years aren't higher than the lowest of your previous highest 35 years of Social Security covered wage-indexed earnings, then Social Security simply won't use those years when calculating your benefit rate.

Best, Jerry