How do you model differential inductor in LTspice?
Follow this answer on modeling a common mode choke, but reverse one of the two coils. 



The K1 Lp1 Ls1 1 (I think there's a typo there) directive sets the coupling to 1 (perfect) which is pretty close to 
reality for a toroidal coil. 

That's for a perfect (linear lossless) inductor with no leakage inductance. If you need to model core loss and such like it's more complicated, but adding leakage inductance is just reducing the coupling factor.