The throughput and sensitivity of the JWST mid-infrared instrument

The Verification Model (VM) of MIRI has recently completed an extensive programme of cryogenic testing, with the Flight Model (FM) now being assembled and made ready to begin performance testing in the next few months. By combining those VM test results which relate to MIRI's scientific performance with measurements made on FM components and sub-assemblies, we have been able to refine and develop the existing model of the instrument's throughput and sensitivity. We present the main components of the model, its correlation with the existing test results and its predictions for MIRI's performance on orbit.