Documenting the Schedule Basis
A schedule shows dates; the basis explains the why — recording the assumptions, methods, and conditions that made those dates. It's what turns a CPM file into a defensible, reviewable, reproducible plan. Built on AACE 38R-06.
What the schedule basis is
The CPM file is necessary but not sufficient. Two planners given the same scope can produce very different schedules because they made different assumptions — about productivity, sequencing, shifts, resources. The basis captures those choices so the schedule is transparent and reproducible, not a black box.
Why it matters — four jobs it does
- Enables review — A reviewer can only judge a schedule if they know its assumptions. "Is 8 days realistic for that pour?" depends on the crew and method the basis records.
- Makes it reproducible — Another planner can rebuild or update the schedule consistently because the logic and data behind it are written down.
- Protects entitlement — In a delay claim, the documented basis is the reference point for what was planned — and what changed. (This is the scheduling cousin of claims protection, Track 6.)
- Aligns stakeholders — It surfaces assumptions for agreement up front — so the owner, contractor, and team commit to the same plan, not different mental versions of it.
What a schedule basis contains
A good basis covers the choices that shaped the dates. Typical contents:
| Section | Records… |
|---|---|
| Scope & references | What's covered, the WBS, drawings/specs and revisions used |
| Methodology | How durations and logic were derived; software and settings |
| Calendars & workweeks | Working days, shifts, holidays, weather allowances |
| Productivity & resources | Rates assumed, crews/equipment, key resource limits |
| Sequencing & strategy | Execution approach, phasing, major preferential logic |
| Constraints & milestones | Contractual dates, access, permits, owner-supplied items |
| Assumptions & exclusions | What was assumed and, crucially, what's not covered |
| Risks & contingency | Known risks and any schedule contingency/float strategy |
When and how to keep it
The basis is written alongside the baseline schedule and issued with it — a schedule submitted without its basis is half a deliverable. Then it's kept alive: each major revision or rebaseline updates the basis to record what assumptions changed and why. A version-controlled basis, paired with each schedule version, is the audit trail that makes the schedule credible from day one to closeout.
Ten things to remember
- The schedule basis records why the schedule says what it says — the bars' companion narrative.
- The CPM file alone is a black box — assumptions made the dates, and they must be written down.
- It's the scheduling cousin of the basis of estimate — same role, applied to time.
- Write it as you build — capture assumptions while they're fresh, not after the fact.
- It enables review, reproducibility, entitlement protection, and stakeholder alignment.
- Cover scope, methodology, calendars, productivity/resources, sequencing, constraints, assumptions, risks.
- State exclusions clearly — what the schedule does not assume protects you later.
- Issue the basis with the schedule — a schedule without its basis is half a deliverable.
- Update it at every rebaseline — version it alongside the schedule for a clean audit trail.
- Even a short basis beats none — the discipline matters more than the page count.
Glossary
- Assumption
- A condition taken as true for planning (e.g. permits by March).
- Audit trail
- The versioned record of schedules and their bases over time.
- Basis of estimate
- The cost-side equivalent — the assumptions behind an estimate.
- Constraint
- An external or contractual date affecting the schedule.
- Exclusion
- Scope or conditions explicitly not covered by the schedule.
- Methodology
- How durations and logic were derived; software and settings used.
- Rebaseline
- Re-establishing the baseline; triggers a basis update.
- Schedule basis
- The documented assumptions, methods, and conditions behind a schedule.