Teams are allowed to define what low-cost means to their project, and many use a combination of the payback period and implementation cost to determine a reasonable threshold. As a widely accepted rule of thumb, measures with a simple payback period of zero to 18 months are considered low-cost, and your team should be prepared to provide justification if the payback threshold is set below 18 months. See the Documentation Toolkit for an example table showing low-cost improvements.