The following are the current rates at September 2012
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Interest on overdue tax
Interest on all unpaid tax is charged at the same rate.
The formula is Bank base rate plus 2.5% which gives a present rate of 3%.
There is one exception: Quarterly instalments of corporation tax bear interest at only 1.5%.
Interest on all overpaid tax is payable at the same rate.
The formula is Bank base rate minus 1% but with an overriding minimum of 0.5% which applies at the present time.
Official rate of interest
From 6 April 2010: 4%