The magnetising inductance falls out from the peak design flux density (B) in the core ( which is usually a function of freq ) - if you have designed for a Bmax of 150mT each way at say 70kHz then the number of turns this turns out to be along with the AL of the ungapped core will give you the Lmag ( N^2 x Al )
you can have more pri turns than this ( to lower Imag, and raise Lmag ) or you can gap the core slightly to lower Lmag and raise Imag...
sometimes a lower Lmag ( higher Imag ) is useful to extend soft switching to lower values of load...
good luck ...!