In which type of billing schedule does billing occur based on the percent work completed?

The most appropriate billing schedule for situations where billing is based on the percentage of work completed is the Time and Materials Billing Schedule. This type of schedule allows for charges to reflect actual work done and materials used, enabling billing to progress based on the completion percentage of the overall task or project. As work is completed, costs can be billed proportionately, aligning payments with the practical advancement of the project.

This billing method provides flexibility for project-based work, where the final costs can be uncertain at the start. It allows for partial payments as each segment of work is finished, which benefits both the provider and the client by ensuring that payment corresponds to actual progress.

With the other options, while they each have specific billing mechanisms—like Fixed Bid Milestone Billing that works on completing specific milestones rather than ongoing work progress, or Standard Billing that usually follows predetermined cycles—none fit the method of billing solely based on the percentage of work completed as aligned with the characteristics of a Time and Materials Billing Schedule.