1. A capacity modeling system, for creating a capacity model, comprising: a memory device; a communication device; and a processing device, operatively coupled to the memory device and the communication device, and configured to execute computer-readable program code to: capture transactional data for an application; run a window run-time estimator model based on the transactional data, wherein the window run-time estimator model is a model comprising specific steps for each job in a window; apply constraints to the capacity model, wherein the constraints are based on capabilities of the application and systems on which the application is run; run a shift run-time estimator model based on the window run-time estimator model and the constraints, wherein the shift run-time estimator model determines an estimated transactional capacity of a shift, wherein a shift comprises multiple window runs and interspersed intra-window runs; calculate a transaction capacity of the application; and compare volume forecasts with the transaction capacity of the application to determine when the transaction capacity needs to be addressed.