  We calculate analytically the dynamic critical exponent $z_{MC}$ measured in
Monte Carlo simulations for a vortex loop model of the superconducting
transition, and account for the simulation results. In the weak screening
limit, where magnetic fluctuations are neglected, the dynamic exponent is found
to be $z_{MC} = 3/2$. In the perfect screening limit, $z_{MC} = 5/2$. We relate
$z_{MC}$ to the actual value of $z$ observable in experiments and find that $z
\sim 2$, consistent with some experimental results.
