Senior citizens in 47 states and the District of Columbia aren’t replacing enough of their pre-retirement incomes, according to a new Bankrate.com study. Many financial experts believe retirees need at least 70 percent of the income they earned in their working years, but only seniors in Hawaii, Alaska and South Carolina meet that threshold. Iowa has the 11th-largest retirement gap, with retirement funds among Iowa retirees replacing 56 percent of their pre-retirement income, which averages $66,128, the study found. Nationally, the median income for those who are 65 and older is just 60 percent of the median income among 45 to 64 year-olds. The 15 states with the largest retirement income gaps are all located in the northern half of the country; Massachusetts has the largest gap.