This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by NPG. ; Metal-halide perovskites are at the frontier of optoelectronic research due to solution-processability and excellent semiconductor properties. Here, we use transient absorption spectroscopy to study hot carrier distributions in CH_3NH_3PbI_3 and quantify key semiconductor parameters. Above-bandgap, non-resonant excitation creates quasi-thermalized carrier distributions within 100 fs. During carrier cooling, a sub-bandgap transient absorption signal arises at ~1.6 eV, which is explained by the interplay of band-gap renormalization and hot carrier distributions. At higher excitation densities, a ?phonon bottleneck? substantially slows carrier cooling. This effect indicates low impurity and phonon-phonon scattering in these polycrystalline materials, which contributes to high charge carrier mobilities. Photoinduced reflectivity changes distort the shape of transient absorption spectra and must be included to extract physical constants. Using a simple band-filling model that accounts for these changes, we determine a small effective mass of m_r = 0.14 m_o, which agrees with band structure calculations and high photovoltaic performance. ; We thank the Engineering and Physical Sciences Research Council, and the Winton Programme (Cambridge) for the Physics of Sustainability for funding. M.B.P. wants to thank the Cambridge Commonwealth Trust and the Rutherford Foundation of New Zealand for funding. F.D. acknowledges funding from a Herchel Smith Research Fellowship.