HKSM
Buffer
A buffer is a planned margin of time, cost, or resources added to a schedule or budget to absorb uncertainty and keep key commitments on track. Buffers may cover known risks (contingency) or unforeseen events (management reserve), and their use is tracked and controlled.
Key Points
- Purpose: protect dates, scope, and budgets from normal variation and risk impacts.
- Types: contingency for identified risks; management reserve for unknowns; schedule buffers such as project and feeding buffers in critical chain.
- Placement and sizing: added at control points (e.g., end of critical path or before merges) and sized using risk analysis or historical data.
- Governance: consumption is monitored; contingency is managed by the project manager, while management reserve typically needs sponsor approval.
Example
A construction project adds a 10% cost contingency and a 2-week project buffer at the end of the critical path. When a supplier shipment slips by 5 days, the team draws from the buffer, keeping the final completion date unchanged.
PMP Example Question
Which option best describes the primary purpose of a buffer in a project plan?
- Unused float that any activity can take without affecting successors
- Extra time or budget set aside to absorb uncertainty and protect commitments
- Overtime scheduled to accelerate critical activities
- Padding added by team members without analysis
Correct Answer: B — Extra time or budget set aside to absorb uncertainty and protect commitments
Explanation: A buffer is a planned allowance to handle variability and risks so that dates and budgets are maintained; it is not float, forced overtime, or unsubstantiated padding.
