Diversify S&P 500 portfolio with bonds, international, and mid/small caps.

The user is seeking advice on diversifying a 100% S&P 500 portfolio (FXAIX) as they approach retirement age (48/50). The proposed strategy to add 15% bonds, 15% international, and 15% extended market (mid/small cap) funds is a sound financial planning move to reduce volatility and improve risk-adjusted returns compared to a highly concentrated S&P 500 position. This offers a 'cushion' for market downturns, which is prudent for those with shorter investment horizons. While some comments debate the timing of bonds due to inflation, the general consensus for diversification as one ages remains strong in financial advice.