Year Percent 1950 4.20957 1955 3.88063 1960 3.75441 1965 3.73637 1970 3.74342 1975 3.77536 1980 3.81127 1985 3.82506 1990 4.00222 1995 3.85792 2000 3.4542 2005 3.2114 2010 3.00473 2015 2.87579 2020 2.81157 2025 2.89634 2030 3.20259 2035 3.67215 2040 4.21844 2045 4.80377 2050 5.44725 2055 6.21289 2060 7.09923 2065 8.15843 2070 9.34812 2075 10.61661 2080 11.94631 2085 13.33554 2090 14.76925 2095 16.22101 2100 17.67379