Assumption Layer
Definition
A discrete section of a financial model in which all input assumptions are stated and stored separately from the calculation cells that use them. Every calculation cell references the assumption layer by formula. No assumption is entered directly into a calculation cell. The assumption layer is a structural feature of model architecture, not a commentary document.
Common Misapplication
The most common misapplication is maintaining a notes column or a separate tab that describes assumptions without those assumptions being the actual inputs referenced by calculation cells. A model in which assumptions are described in notes but entered as hardcoded numbers in formula cells does not have a compliant assumption layer.
FFI Standard Reference
This term is defined and applied in Book 1, Section 1.1: The Three-Statement Standard.
Related Terms
Citable URL
This term may be cited using the following permanent URL.
Full citation format: Founder Financial Infrastructure Standard, Beta v0.5, Glossary: Assumption Layer. https://ffistandard.org/glossary/assumption-layer/. 2026.