A cost model is only as good as its last update.
A cost model is not a static artifact. It represents how your business consumes resources, and that consumption changes every time you add a product, shift a process, or change volumes. This question reveals whether your model keeps pace with reality or quietly drifts away from it.
“How often do you review and update your cost model?”
How often should a cost model be reviewed and updated?
As often as the business changes, not on a fixed calendar out of habit. A cost model drifts from reality every time processes, resource costs, volumes, or the product mix shift, and research attributes roughly 49% of costing errors to model specification and about 21% to a lack of updating. A mature approach is event-driven: the model is refreshed whenever a significant change occurs, not only once a year. The alternative is a model that looks precise while quietly guiding pricing and portfolio decisions with cost data that no longer reflects how the business actually runs.
A stale model is confidently wrong.
A cost model represents how the business consumes resources today. The moment processes change, equipment is replaced, or volumes shift significantly, the model must reflect it, or every decision built on it uses out-of-date information while looking authoritative.
Research on sources of error in costing systems identifies three main categories: about 49% of errors come from incorrect model specification, 30% from imprecise parameter estimates, and 21% from a lack of updating. That last component is especially insidious because it accumulates gradually and silently.
The critical distinction is between calendar-based and event-driven updates. Many organizations refresh on a fixed cadence, typically annual or semi-annual. Better than never, but an event-driven approach is fundamentally superior: the model is updated whenever a significant change occurs in processes, resource costs, or the time equations that underpin the costing.
Review moves from never to event-driven.
As review discipline matures, the model goes from never updated to annual, quarterly, and finally event-driven, and the orange distortion band shrinks toward a live model that tracks the business.
How current is your model?
Question 2 assesses how well your cost model keeps pace with a changing business. Each level reflects a smaller gap between what the model says and how the business actually runs today.
“We do not maintain a formal cost model that is kept up to date.”
There is no living cost model to update. Costs are estimated ad hoc when a decision demands it, using whatever data is at hand. Nothing accumulates, so the business cannot see how its cost structure is changing or which decisions rest on stale assumptions.
- No maintained model exists to keep current
- Cost estimates are rebuilt from scratch each time
- Cost-structure change over time is invisible
- Decisions rely on undocumented, one-off assumptions
“We review and update the cost model once a year.”
A cost model exists and is refreshed annually, usually alongside the budget. This gives a documented baseline, but a year is long enough for processes, volumes, and resource costs to move materially, so for much of the year the model runs behind reality.
- The model can be up to twelve months behind reality
- Mid-year changes are not reflected until the next cycle
- Pricing and portfolio decisions use aging rates
- The annual refresh competes with budget-season pressure
“We review and update the cost model every quarter.”
The model is refreshed on a quarterly cadence, so it never drifts more than three months from reality. This is enough discipline for most businesses, catching seasonal shifts and significant changes within a reasonable window, though a fast-moving change can still wait weeks for the next review.
- A fast-moving change can still wait for the next quarter
- The cadence may not match the pace of the business
- Review can become routine rather than triggered by change
- Some parameters may need more frequent attention than others
“We update the model monthly or whenever a significant change occurs.”
The model is treated as a living system. It is refreshed monthly and, more importantly, whenever a material change happens: a new product, a process shift, a change in resource cost, or a move in volume. Cost data stays close to reality, so pricing, portfolio, and capacity decisions rest on a model that tracks the business.
- Event-driven updates need a trigger and a clear owner
- Frequent updates demand clean, accessible source data
- Discipline is needed so minor noise does not cause churn
- Version control keeps the model auditable as it changes
Practical steps, level by level.
Quick Wins
- Build a first simple cost model, even a spreadsheet, that captures how cost is consumed
- Document its assumptions so the next update has a baseline to work from
- Set a date to review it against actuals at least once a year
- Compare the model to reality once and note where it already drifted
Structural Improvements
- Move from an annual to a quarterly review cadence
- Define which parameters to check each quarter: rates, volumes, process times
- Build a short checklist so the review is repeatable, not reinvented
- Log each change so the model’s history is auditable
World-Class Practices
- Define the events that trigger an update: new product, process change, cost shift
- Assign a clear owner so triggered updates actually happen
- Refresh TDABC time equations whenever the underlying process changes
- Add version control so every change is dated, documented, and reversible
How fast the model goes stale.
The right cadence follows the pace of change, which differs by industry, but the direction is the same: the faster the business moves, the shorter the review interval must be.
| Industry | Cadence | Key Insight |
|---|---|---|
| Manufacturing | Quarterly+ | Process changes and new lines move cost fast; event-driven updates to time equations keep product cost honest between quarters. |
| Distribution & Logistics | Monthly | Carrier rates, fuel, and volumes shift often; cost-to-serve drifts within weeks, so monthly or event-driven review is the safe floor. |
| Professional Services | Event-driven | Cost is people time; whenever a workflow or role mix changes, the time equations must be refreshed or quotes carry stale effort. |
Is your cost model live, or a year behind?
Take the free Profitability Health Check to assess how well your cost model keeps pace with your business, and where stale data is quietly steering decisions.