From ACT Wiki
The quotation of a rate of return, or a cost, on the basis of a nominal annual rate for compounding twice per year.
A rate of return - quoted as an annual effective rate - is 4.04%.
What is this same rate of return quoted on a semi-annual basis?
The same rate of return quoted on a semi-annual basis is:
(1.0404(1/2) -1) x 2
It is sometimes written as semiannual, without the hyphen.