An apparatus and method are provided for performing arithmetic operations to accumulate floating-point numbers. The apparatus comprises execution circuitry to perform arithmetic operations, and decoder circuitry to decode a sequence of instructions. A convert and accumulate instruction is provided, and the decoder circuitry is responsive to decoding the convert and accumulate instruction to generate one or more control signals to control the execution circuitry to convert at least one floating-point operand identified by the convert and accumulate instruction into a corresponding N-bit fixed-point operand having M fraction bits, where M is less than N and M is dependent on a format of the floating-point operand. The execution circuitry accumulates each corresponding N bit fixed-point operand and a P bit fixed-point operand identified by the convert and accumulate instruction in order to generate a P bit fixed-point result value, where P is greater than N and also has M fraction bits.