The Assumption Log is a living document that records all assumptions and constraints identified throughout the project lifecycle. In the PMBOK Guide 8th Edition, the Assumption Log is a key output of the Initiate Project or Phase process within the Governance Performance Domain. Every project is built on assumptions — factors believed to be true but not yet verified — and this assumption log template ensures they are systematically tracked, validated, and managed to prevent unpleasant surprises.

Why You Need an Assumption Log Template

Unmanaged assumptions are hidden risks. When an assumption proves false, it can trigger cost overruns, schedule delays, or scope changes. A structured assumption log template captures each assumption with its category, impact assessment, validation approach, and current status. By reviewing the log regularly, project managers can proactively identify assumptions that are becoming invalid and trigger appropriate risk responses before damage occurs. This assumption log template also distinguishes between assumptions (believed true) and constraints (known limitations), ensuring both are managed with appropriate rigor. Organizations that maintain disciplined assumption tracking consistently demonstrate better project predictability.

Template Sections

This assumption log template is an Excel spreadsheet with the following columns and features:

1. Assumption/Constraint ID — Unique identifier for traceability
2. Type — Dropdown: Assumption or Constraint
3. Category — Classification (Technical, Organizational, Resource, External, Financial)
4. Description — Clear statement of the assumption or constraint
5. Impact if Invalid — Dropdown: High, Medium, Low — with conditional formatting
6. Validation Approach — How and when the assumption will be verified
7. Status — Dropdown: Open, Validated, Invalid, Closed — with conditional formatting
8. Owner — Person responsible for monitoring and validating
9. Action Required — Next steps if the assumption is invalidated
10. Date Identified / Target Validation Date — Timeline tracking

PMBOK 8 Features

• Excel Dropdowns — Pre-built dropdown lists for Type, Impact, and Status fields ensure data consistency and enable filtering
• Conditional Formatting — Visual color-coding for impact levels (red for High, yellow for Medium, green for Low) and status tracking
• Assumption-to-Risk Linkage — When an assumption is invalidated, the log prompts creation of a corresponding risk entry, supporting PMBOK 8's integrated approach to uncertainty management
• Governance Domain Alignment — Structured governance of assumptions from project initiation through closure

Related PMBOK 8 Templates

Complete your project initiation toolkit with these related templates:

• Project Charter — PMBOK 8
• Risk Management Plan — PMBOK 8

Format: Microsoft Excel (.xlsx) | PMBOK Edition: 8th (2025) | Domain: Governance | Process: Initiate Project or Phase