How to calculate the current in a PWM LED driver circuit?
The equation you are using is to calculate the ripple current, The peak-peak current. Your DMM will not be able to measure this 



The next two equations are needed to determine the current

\$I_{max out} = (I_{limmin} - \frac{\Delta I_L}{2}) * (1-D)\$ 

\$I_{swmax} = \frac{\Delta I_L}{2} + \frac{I_{max out}}{1-D} \$