What is the accretion rate in NGC 4258?

We estimate the accretion rate Ṁ onto the black hole in the nucleus of NGC 4258. The result is model dependent. We find that a thin disk that is flat out to ≳2 × 10³GM/c² (M ≡ black hole mass) and that has inclination equal to that of the masing disk must have Ṁ ≃ 0.01 M_⊙ yr^-1 for consistency with near-infrared data. A thin disk that is warped at ∼10³GM/c² requires Ṁ ≳ 1.5 × 10^-4 M_⊙ yr^-1 for consistency with near-infrared data. Reasonable warp models and the near-infrared data are not consistent with Ṁ as low as the 7 × 10^-5α M_⊙ yr^-1 proposed by Neufeld & Maloney. An advection-dominated flow model combined with the X-ray data implies Ṁ ≃ 0.01 M_⊙ yr^-1. Consistency with a tight 22 GHz upper limit on the flux from the central source requires a transition radius of ∼(10-100)GM/c², although the 22 GHz upper limit may be relaxed by appeal to free-free absorption. Physical conditions in the observed VLBI jet features can also be related to conditions in the inner accretion flow. We conclude with a list of observations that might further constrain Ṁ.