Planning for Retirement: Is it more cost-effective to invest in Shenzhen's social security fund or the S&P 500 index fund? Grok calculated it: Assuming a monthly investment of $400 in an S&P 500 index fund for 20 years (240 months), using a monthly investment method, the total principal would be $96,000. Ignoring USD/CNY exchange rate fluctuations: The S&P 500 has grown at an average annual rate of about 10% over the past 50 years. Assuming this continues, after 20 years it would be $303,748, yielding an annual investment return of approximately $30,000, or about 210,000 RMB, or about 17,000 RMB per month. Assuming an average annual growth rate of about 7% over the next 20 years, it would be $2,077,480, yielding an annual investment return of approximately $14,000, or about 100,000 RMB, or about 8,300 RMB per month. How much would you receive from social security? 3,000?