ADVISORY
By Dr. Kenneth Smith, PMP
Honolulu, Hawaii, USA
& Manila, The Philippines
“It’s better to have it and not need it
than to need it and not have it.”
George Ellis
After carefully planning a project’s critical path, how much ‘extra’ Management Reserve time should you pad the estimated duration for unanticipated delays: 10% 15% 25% just in case, or even more? Is there a ‘rule of thumb’ for your particular sector?
A synopsis — gleaned from AI — identified the following extant practices:
-
- 20% Solution
- 25% Minimum Rule
- Rule of 30%: Add 30% to the estimated critical path.
- 50% — aka — Goldratt Rule:[1] Schedule project activity durations at 50% probability,
then add a 50% buffer to the end of the critical path
-
- “Cut and Paste” Cut individual “safe” task durations in half, then add that time to a combined end buffer.
- Strategic Placement:[2] Rather than one large end blob,
- Resource Buffers: Add ‘something’ to selected key activities throughout
- Feeder Buffers: Add ‘something’ to non-critical activities that merge with the critical path
Depending how many thumbs — &/or fingers — you are willing to contribute to the estimating effort, ‘Risk & Remedy’ is yet another approach for your consideration, based on individual critical path activity probabilities. I applied and advocated this methodology for many years;[3] and recently upgraded the related Excel template, as shown in Figure 1 to facilitate number-crunching.
More…
To read entire article, click here
How to cite this article: Smith, K.F. (2026). Project Management Reserve Buffering. PM World Journal, Vol. XV, Issue VI, June. Available online at https://pmworldjournal.com/wp-content/uploads/2026/06/pmwj165-Jun2026-Smith-Project-Management-Schedule-Buffering.pdf
About the Author
Dr. Kenneth Smith
Honolulu, Hawaii
& Manila, The Philippines
Initially a US Civil Service Management Intern, then a management analyst & systems specialist with the US Defense Department, Ken subsequently had a career as a senior foreign service officer — management & evaluation specialist, project manager, and in-house facilitator/trainer — with the US Agency for International Development (USAID). Ken assisted host country governments in many countries to plan, monitor and evaluate projects in various technical sectors; working ‘hands-on’ with their officers as well as other USAID personnel, contractors and NGOs. Intermittently, he was also a team leader &/or team member to conduct project, program & and country-level portfolio analyses and evaluations.
Concurrently, Ken had an active dual career as Air Force ready-reservist in Asia (Japan, Korea, Vietnam, Indonesia, Philippines) as well as the Washington D.C. area; was Chairman of a Congressional Services Academy Advisory Board (SAAB); and had additional duties as an Air Force Academy Liaison Officer. He retired as a ‘bird’ colonel.
After retirement from USAID, Ken was a project management consultant for ADB, the World Bank, UNDP and USAID.
He earned his DPA (Doctor of Public Administration) from the George Mason University (GMU) in Virginia, his MS from Massachusetts Institute of Technology (MIT Systems Analysis Fellow, Center for Advanced Engineering Study), and BA & MA degrees in Government & International Relations from the University of Connecticut (UCONN). A long-time member of the Project Management Institute (PMI) and IPMA-USA, Ken is a Certified Project Management Professional (PMP®) and a member of the PMI®-Honolulu and Philippines Chapters.
Ken has two KENBOOKS: 1. Project Management PRAXIS which includes many innovative project management tools & techniques; and describes a “Toolkit” of related templates, and 2. MUSINGS on Project Management — a compilation of contemporary concerns in project planning, monitoring & evaluation, with some tools & techniques suggested for their solution. Either or both books are available from Amazon, and their related templates are available directly from him at kenfsmith@aol.com on proof of purchase.
To view other works by Ken Smith, visit his author showcase in the PM World Library at https://pmworldlibrary.net/authors/dr-kenneth-smith/
[1] See my detailed reaction in Smith, K. F. (2023). On Critical Chain Scheduling & Buffering: A Critique on the Theory of Constraints as Applied to Project Management, advisory article, PM World Journal, Vol. XII, Issue I, January. https://pmworldlibrary.net/wp-content/uploads/2022/12/pmwj125-Jan2023-Smith-on-critical-chain-scheduling-and-buffering.pdf
[2] See a couple of my suggestions in Smith, K. F. (2025). Slipped Schedules, Touch-Time, and Black Elephants! Advisory article, PM World Journal, Vol. XIV, Issue II, February. https://pmworldlibrary.net/wp-content/uploads/2025/02/pmwj149-Feb2025-Smith-slipped-schedules-touch-time-black-elephants.pdf
[3] Smith, K. F. (2022). Schedule Slippages, Root Causes & Recommended Remedies, PM World Journal, Vol. XI, Issue V, May. https://pmworldlibrary.net/wp-content/uploads/2022/05/pmwj117-May2022-Smith-schedule-slippages-root-causes-remedies.pdf
