To determine periodic interest rate is the formula( 1 + EAR/m) ^ 1/m used???

So a 20 year $150 000 mortgage with monthly payments at a rate of 6.8 % per year compounded semi annually would have an EAR of ( 1 + 0.068/2)^2-1

=0.069156

Then for periodic (Monthly)rate, that would equal ( 1 + EAR/12)^ 1/12 ????