How to Write a Schedule Basis Memo (with a Checklist)
What Is a Schedule Basis Memo and Why Does It Matter?
A schedule basis memo (SBM) is a living document that records the key assumptions, constraints, and methodology used to develop a baseline schedule. It answers questions like: Why were certain durations chosen? Which calendars apply? What sequencing logic drives the critical path? In forensic delay analysis, the SBM is often the first document scrutinized. Without it, you leave your schedule open to interpretation — and that can cost you in a dispute.
Think of the SBM as the “user manual” for your Primavera P6 XER file. It bridges the gap between the raw schedule data and the project team’s intent. A well-written memo can strengthen a delay claim; a missing or vague one can sink it.
What to Include in Your Schedule Basis Memo
A comprehensive SBM covers five core areas. Below is what each section should contain.
1. Calendars and Working Days
List all calendars used (e.g., 5-day, 7-day, weather-impacted). For each, specify the working days, non-working periods, and any exceptions. If a calendar includes holidays or shutdowns, note them. Example: “Calendar ‘Concrete Crew’ uses a 6-day workweek with Sundays off, plus 10 company holidays.”
2. Activity Coding and WBS
Describe the Work Breakdown Structure (WBS) and activity coding scheme. Explain how codes like “Area,” “Discipline,” or “Phase” are used to filter and sort activities. This helps analysts understand the schedule’s taxonomy.
3. Duration and Logic Assumptions
Document how durations were estimated (e.g., historical data, vendor quotes, productivity rates). State the default relationship type (usually FS) and any use of leads/lags. If you applied constraints (e.g., “Start No Earlier Than” for a permit), list them with justification.
4. Sequencing and Critical Path Methodology
Explain the overall sequencing strategy — for example, “Floor-by-floor, with MEP following structure by two floors.” Clarify how the critical path was determined (e.g., longest path vs. total float). If you used any schedule analysis tools (like DCMA 14-point checks), mention that.
5. Risk and Contingency
Note any schedule contingency (e.g., “5% duration buffer added to procurement activities”). Describe risk mitigation actions that influenced the schedule logic. If you ran Monte Carlo simulations, include the confidence level.
Common Omissions That Hurt Credibility
Even experienced schedulers sometimes skip these details:
- Missing calendar definitions: A “5-day calendar” without specifying which days are non-working is ambiguous.
- No justification for constraints: Mandatory constraints like “Finish No Later Than” without a reason (e.g., “contractual milestone”) raise red flags.
- Vague logic descriptions: Saying “activities are linked in sequence” is useless. Be specific: “Excavation must finish 2 days before footing pour begins.”
- Ignoring external dependencies: If a utility connection depends on a third party, state that and how it’s modelled (e.g., with a constraint or a separate activity).
How to Verify Your Schedule Before Writing the Memo
Before you draft the SBM, run your baseline through a schedule quality check. Tools like Project Assure can run DCMA 14-point, GAO, and NASA checks directly in your browser — no upload needed. This helps you catch logic errors, missing relationships, or questionable constraints that you should explain in the memo. For example, if the DCMA check flags “long lags,” you can document why those lags exist (e.g., “curing time”).
Schedule Basis Memo Checklist
Use this reusable checklist to ensure your SBM is complete. Print it, paste it into your project binder, or keep it as a template.
| # | Item | Status |
|---|---|---|
| 1 | Project name, number, and baseline date | ☐ |
| 2 | List of all calendars with working/non-working days | ☐ |
| 3 | WBS structure description and coding scheme | ☐ |
| 4 | Duration estimating method (historical, vendor, etc.) | ☐ |
| 5 | Default relationship type and any leads/lags | ☐ |
| 6 | All constraints with justification (including calendar constraints) | ☐ |
| 7 | Sequencing narrative (e.g., “structure precedes MEP by 2 floors”) | ☐ |
| 8 | Critical path definition (longest path or total float threshold) | ☐ |
| 9 | Schedule contingency and how it’s applied | ☐ |
| 10 | External dependencies and third-party milestones | ☐ |
| 11 | Risk events that influenced logic or duration | ☐ |
| 12 | Schedule quality check results (e.g., DCMA 14-point) | ☐ |
| 13 | Revision history and approval signatures | ☐ |
Final Tips for a Defensible Memo
- Write it before the baseline is set. Don’t reconstruct assumptions later — document them as you build the schedule.
- Keep it updated. If a change order modifies a key assumption, revise the SBM and note the version.
- Be honest. If you used a “best guess” for a duration, say so. Transparency builds credibility.
- Use plain language. Avoid jargon that a non-scheduler (like a project manager or lawyer) might misinterpret.
A schedule basis memo is not a bureaucratic formality — it’s your schedule’s defense. With this checklist, you can produce one that stands up to scrutiny and supports your project controls process.
Run these checks free, in your browser
Free, browser-based Primavera P6 XER schedule analyser — DCMA 14-point, GAO & NASA checks, EVM/S-curve, and forensic baseline-vs-update comparison. Nothing is uploaded; your XER is parsed locally in the browser. 3 free analyses, no card required.
Analyse your XER →Frequently asked questions
What is the difference between a schedule basis memo and a narrative?
A schedule basis memo focuses on the technical assumptions, calendars, and logic used to build the schedule. A narrative is broader, often describing project scope, milestones, and execution strategy. The SBM is a subset of the narrative, but more detailed on scheduling methodology.
How often should I update the schedule basis memo?
Update it whenever the baseline schedule is revised (e.g., after a major change order or a re-baseline). For ongoing projects, review it at each update cycle to ensure assumptions still hold. In forensic analysis, the version at the time of the baseline is most critical.
Can I use a schedule basis memo to support a delay claim?
Yes. A well-documented SBM helps prove that your baseline was realistic and that delays were not caused by flawed assumptions. It provides a contemporaneous record of intent, which is highly persuasive in disputes.
What happens if I don't have a schedule basis memo?
Without an SBM, you rely on oral testimony or post-hoc rationalization, which is weaker. Opposing experts may argue that assumptions were arbitrary. In some contract specifications (e.g., USACE, DOE), an SBM is mandatory.
Should I include the schedule basis memo in the XER file?
No, the SBM is a separate document (PDF or Word). However, you can reference it in the XER’s project notes or a UDF. The memo should be stored with the baseline schedule files for easy retrieval.