The assets of the Old-Age, Survivors, and Disability Insurance Trust Funds represent the the accumulation over time of the difference between income and outgo. The growth of the assets from the end of December 1986 through the end of September 2013 is shown below by calendar quarter.
Assets grew from about $47 billion at the end of December 1986 to about $2,756 billion ($2.8 trillion) by the end of September 2013.
Note that there is much more seasonality in trust fund income compared to trust fund outgo. There are 2 reasons for seasonality in the quarterly income figures.
- Tax income reaches a peak in the second calendar quarter when many self-employed people pay their taxes with their income tax returns. After the second quarter, tax income falls as earnings of more and more people reach the taxable maximum for Social Security.
- Interest on special-issue securities is paid on June 30 and December 31. While relatively small amounts of interest are paid in every month when securities are redeemed, interest income is always largest in the second and fourth quarters.