How should I log revisions to a financial projection?

Preserve each version

Give each projection a clear date, version identifier and author. Retain the prior version rather than overwriting it. Keep the underlying assumptions, calculation method and source documents alongside the model, with suitable access restrictions for personal financial information.

Explain the revision

For each change, record the field changed, previous and revised basis, reason, evidence source and date received. Distinguish an actual new fact—such as a written lender term—from a changed estimate or preference. Note whether the change affects income, costs, timing, currency, financing or intended use. Identify calculations and downstream assumptions that need updating, and record any unresolved items. Where a value is unknown, label it clearly rather than inserting an unsupported figure.

Have a second person check material edits and preserve a short summary of the overall effect. Ask a qualified financial adviser to review investment suitability implications and an accountant to check accounting or tax assumptions; neither review necessarily validates unrelated legal or technical inputs. Include a review date and triggers for another update, such as a revised offer or confirmed operating cost. A version log makes changes auditable, but does not make forecasts certain. Keep the projection consistent with the records supplied to lenders and advisers, and correct errors transparently.