Beff parameter and saturation current

Hello i have  created 25uA  current threw the nmos and pmos at gpdk45nm technology for the purpose of creating an opamp.

For NMOS in gate drain connection(saturation): W=120n L=1.2u 

After simulating i got the desired result of 24.9uA current. 

beff_nmos=22.7492u (mobility*Cox)

Vth_nmos=320.23m (threshold)

However when i tried to put it in the saturation current formula shown bellow it gives me a result 5 times lower then simulated.

Where did i go wrong interpreting the Model parameter table shown bellow?maybe i should take other parameter instead of Beff to get the fomula match the simulation?

Thanks

I_nmos=C_ox*mobility*0.5*(W/L)*(Vgs-Vt)^2=beff*0.5*(W/L)*(1.8-0.320)^2=22.74*10^-6*0.5((240*10^-9)/(1.2*10^-6))(1.8-0.320)^2=4.9809696 × 10^-6

NMOS:
Vth_nmos=320.23m (threshold)

PMOS parameters

Vt=-0.315