IRS increases interest rates on overdue taxes after March 31, 2011!
Subsequent to March 31, 2011, the IRS announced that "interest rates on outstanding IRS tax obligation will increase by 1%."
The IRS will charge 4% for overdue taxes on individual taxpayers, whereas the amount assessed to corporations will be 6% that owe more than $100,000.
Regarding possible tax refunds, they pay 4% to individuals and 3% to corporations. However, for corporate tax refunds exceeding $10,000, the rate will increase by 1.5%.