Year Percent 1950 15.34103 1955 16.75286 1960 18.17753 1965 19.36831 1970 20.14892 1975 20.45024 1980 19.08552 1985 19.69606 1990 24.07145 1995 23.38652 2000 23.80868 2005 24.92835 2010 25.77077 2015 26.64725 2020 28.60135 2025 31.39893 2030 34.1871 2035 35.75576 2040 36.65486 2045 37.99343 2050 39.04082 2055 39.7442 2060 39.5129 2065 39.08138 2070 38.73544 2075 38.61571 2080 38.76548 2085 38.97182 2090 39.15763 2095 39.32628 2100 39.55984