A data processing apparatus and method includes multiplier logic operable to multiply the first and second n-bit significands to produce a pair of 2n-bit vectors. Half adder logic is arranged to produce a plurality of carry and sum bits representing a corresponding plurality of most significant bits of the pair of 2n-bit vectors. The first adder logic then performs a first sum operation with a first rounded result and a second adder logic performs a second sum operation with a second rounded result. The required n-bit result is then derived from either the first rounded result or the second rounded result. The data processing apparatus takes advantage of a property of the half adder form to enable a rounding increment value to be injected prior to performance of the first and second sum operations without requiring full adders to be used to inject the rounding increment value.