Yeah I see what FVM is saying, since it's not primary current that saturates the core, but magnetizing current, which is different, and is derived from the volt-time product (and the number of turns). So just use the normal V*t=B*A*N equation (though instead of using V.t you'll have to make it an integral as FvM implies).
Defining a saturation current only really makes sense for flyback converters, or choke inductors, where the primary current is only magnetizing, not coupled.