Home >

Appendix: Buffers definitions in USA

Meet the author:

Tal Levanon – Founder and partner in “Tal Levanon – HCP Ltd”, an expert project scheduling consultant and creator of the Hidden Critical Paths (HCP).


This post has been written by three schedule experts (alphabetically): 

Levanon, Tal – CTO and co-owner of Tal Levanon – HCP Ltd., https://www.hcp-consulting.com

Lupu, Toni – Founder-Owner, PBM, toni@pbm.co.il;

Morag, Assaf – CEO, Rakia, https://www.rakia-eng.co.il/;


The largest organization in the western world to set rules and norms on buffer issues is the AACE (American Association for Cost Estimate).


Since AACE deals with both time issues and cost issues, it separates the use of different terms into different areas.


Management Reserve deals only with financial reserves, while Management Schedule Reserve deals with time reserves only.


The term Contingency is reserved for financial issues, while the Schedule Contingency is the buffer, schedule-wise.


Following is the definition of Schedule Contingency:

AACE® International Recommended Practice No. 70R-12, Principles of schedule contingency management as applied in engineering, procurement, and construction:

HCP app | Appendix: Buffers definitions in USA - Schedule management

AACE has defined the ownership of the Buffer (Float) in a decisive and simple way – the Buffer belongs to the contractor.

AACE® International Recommended Practice No. 29R-03

Ownership of Float

Project float is the time between the last schedule activity on the baseline schedule and the contractual completion date where the contractual completion date is later than the scheduled completion date. In this case, in the absence of contrary contractual language, project float is owned solely by the contractor.

In 10S-90 there are many definitions to many terms:

AACE® International Recommended Practice No. 10S-90, Rev. May 27, 2021:


SCHEDULE CONTINGENCY – (1) Duration added to a schedule activity to allow for the probability of possible or unforeseen events. Use in this manner is not recommended as the contingency is hidden and may be misused. (2) A unique activity used to model specific float available to a project phase. Used in this manner gives ownership of float to those activities and or responsibility entity. (3) The amount of time added to specific activities of a project (or program) schedule to mitigate (dampen/buffer) the effects of risks or uncertainties identified or associated with specific elements of that schedule. Syn.: SCHEDULE BUFFER. See also: SCHEDULE MARGIN. (October 2013)

With HCP-Go, project managers complete
the project successfully.
Want to talk to Tal Levanon about it?

If you answered 'yes' - then we have a solution for you!

The AACE further defines that if the client commits a margin, then that margin is his managerial reserve, outside the project contents, as follows:

SCHEDULE MARGIN (SM) – Schedule margin or schedule reserve are interchangeable terms meaning duration added to a schedule activity to allow for the probability of possible or unforeseen events. It is typically based on a schedule risk assessment and is measured in the unit of the schedule (typically days). For earned value management, schedule margin is usually limited to logical end points within the schedule. Schedule margin acts as a buffer between the baseline activities and the project end date. It may be considered management reserve (MR) in time units. Syn.: SCHEDULE RESERVE. See also: MANAGEMENT RESERVE; SCHEDULE CONTINGENCY. (October 2013)

MANAGEMENT SCHEDULE RESERVE (MSR) – A designated amount of time to account for risks that cannot be quantified and/or managed with contingency, or to allow time for management discretionary purposes and the use of management reserve generally requires a formal baseline change. Management reserves are generally not related to schedule contingency. See also: MANAGEMENT RESERVE (MR). (October 2013)


In other words – do not confuse the different terms. The buffer that belongs to the project owner is not part of the scope of work of the contractor’s contract. The buffer that belongs to the contractor does not include the changes or delays of the project owner.

Leave a Reply

Skip to content