Program Increments (PIs) are the unit of time used on Solution Roadmaps, which are visual tools that forecast and communicate the planned deliverables, milestones, and investments over a time horizon12. PIs are fixed-length timeboxes, typically 8 to 12 weeks long, that provide a regular and predictable planning cadence for the Agile Release Trains (ARTs) and Solution Trains3. PIs are used on Solution Roadmaps to:

*Align the solution delivery with the PI objectives, which are the SMART goals that define the expected outcomes and benefits for each ART and Solution Train in a PI3.

*Coordinate the dependencies and interfaces between the ARTs and Solution Trains that contribute to the solution3.

*Provide a near-term forecast of the features and capabilities that will be delivered in the next two to three PIs12.

*Incorporate feedback and learning from the previous PIs and adjust the scope and priority of the work items as needed12.

Some additional information that might be helpful for you are:

*The other options (A, B, and D) are not the unit of time used on Solution Roadmaps, but rather units of time that may be used for other purposes or in other contexts.

*Iterations are fixed-length timeboxes, typically one or two weeks long, that provide a regular and predictable development cadence for the Agile Teams4. Iterations are used to plan, execute, and demo the work items in the Team Backlog4.

*Years are a unit of time that may be used to provide a high-level overview of the roadmap, outlining major milestones, goals, and initiatives that are planned over multiple years2. Years are not used to plan or forecast the solution delivery in detail, as they are too long and uncertain for Agile planning2.

*Days are a unit of time that may be used to estimate the effort or duration of a work item or a task5. Days are not used to schedule or forecast the solution delivery on the roadmap, as they are too granular and variable for Agile planning5.