Five Mistakes in Building a Financial Model

Mistake 1: An unjustified growth assumption

The most common mistake is that revenue growth is built backward from a target outcome rather than from historical performance or independent market analysis.

A lender's first question is what the growth rate is based on. A growth curve with no justification undermines confidence in the whole model.

Mistake 2: Missing sensitivity analysis

A single-scenario model does not give the information a decision needs. It must show how the outcome changes when critical variables — price, volume, FX rate, interest rate — are moved by a few points.

The absence of sensitivity analysis gives the impression the model was built only to show the most optimistic scenario.

Mistake 3: Circular references and manual contradictions

Structures where interest expense depends on the debt balance, the debt balance depends on cash flow, and cash flow depends back on interest expense will lock up or produce a wrong result if not built correctly.

This is usually seen in models where iterative calculation is switched off or no circularity switch has been built in.

Mistake 4: Ignoring working capital

A model that looks profitable can in fact consume significant cash if receivable collection days, inventory turnover and payable terms are not modelled correctly.

When the change in working capital is not shown as a separate line, the model confuses profit with cash and understates the real financing need.

Mistake 5: No audit trail

If a lender or investor cannot trace where a cell's value comes from, they will not trust the model. Fixed assumptions, formulas and scenario switches should be kept separate and visible.

A good model is one a third party can open a week later and understand how it was built without any explanation.

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