Just found the answer to my question. It is tied to the federals COLA (Cost of Living Increase) This year they state it is 2.7%.
SSI Monthly Payment Amounts, 1975-2005 Year Automatic
increase Eligible
individual Eligible
couple
1975 8.0% $157.70 $236.60
1976 6.4% 167.80 251.80
1977 5.9% 177.80 266.70
1978 6.5% 189.40 284.10
1979 9.9% 208.20 312.30
1980 14.3% 238.00 357.00
1981 11.2% 264.70 397.00
1982 7.4% 284.30 426.40
1983 a 7.0% 304.30 456.40
1984 3.5% 314.00 472.00
1985 3.5% 325.00 488.00
1986 3.1% 336.00 504.00
1987 1.3% 340.00 510.00
1988 4.2% 354.00 532.00
1989 4.0% 368.00 553.00
1990 4.7% 386.00 579.00
1991 5.4% 407.00 610.00
1992 3.7% 422.00 633.00
1993 3.0% 434.00 652.00
1994 2.6% 446.00 669.00
Year Automatic
increase Eligible
individual Eligible
couple
1995 2.8% $458.00 $687.00
1996 2.6% 470.00 705.00
1997 2.9% 484.00 726.00
1998 2.1% 494.00 741.00
1999 1.3% 500.00 751.00
2000 b 2.5% 513.00 769.00
2001 3.5% 531.00 796.00
2002 2.6% 545.00 817.00
2003 1.4% 552.00 829.00
2004 2.1% 564.00 846.00
2005 2.7% 579.00 869.00
a The increase effective for July 1983 was a legislated increase.
bOriginally determined as 2.4 percent based on CPIs published by the Bureau of Labor Statistics. Pursuant to Public Law 106-554, however, the COLA is effectively now 2.5 percent.