You erred in assuming a 5% growth rate in your investment. Because of your membership in the Social Security Trust Fund, you should anticipate a rate of return on the order of -4% excluding regular pillaging of your principal to fund such important national priorities as bridges to nowhere and indoor jungles without which the terrorists will have won. If you cannot understand that knowledge or the benefit thereof to your bottom line, then your level of intelligence differs markedly from that of Distinguished Members of Congress.
Social security returns for those not retired cannot be reliably calculated. Substantial benefit reductions are coming, either directly through increases in retirement age or indirectly through increased taxes and a reduced standard of living. The returns may be much worse than -4%. I prefer direct benefit reductions as the impact on the benefits will be easier to understand. However, the rats prefer indirect reductions so they can hide the real benefit reductions until it is too late. I prefer privatization which form many would be a benefit reduction. However I would have the incentive to fund my own retirement. Social security is a generational Ponzi scheme that will come unraveled in some way.