What Changes When Assumptions Change? The Questions a Useful Financial Model Should Answer

For me, the test of a financial model is fairly simple.

If management changes an important assumption, does the model help explain what changes in the business?

If it does not, the spreadsheet may contain a lot of numbers without being particularly useful for the decision.

A model should start with the decision

Before building formulas, there should be a clear question.

For example:

Should we expand capacity?

Can the business afford to hire this team now?

How much working capital will growth require?

When could additional funding be needed?

What happens if sales take longer to build than expected?

The model should be designed around the decision being considered, not around showing how complicated the spreadsheet can become.

What assumptions actually drive the result?

Every forecast depends on assumptions.

Revenue growth is an assumption.

Gross margin may be an assumption.

Customer collection periods, supplier payment terms, staff costs, capital expenditure and financing terms can all materially affect the outcome.

A useful model should make those drivers visible.

Management should be able to understand:

What have we assumed?

and

Which assumptions matter most?

If the important assumptions are buried inside dozens of formulas, the model becomes difficult to challenge and difficult to use.

What happens to cash?

This is one of the most important questions.

A business plan can look attractive on the profit and loss account while creating significant cash pressure.

That may happen because of:

• working-capital requirements;
• capital expenditure;
• debt repayments;
• timing differences;
• upfront expansion costs; or
• slower customer collections.

A useful financial model should therefore connect the operating plan to cash movement.

Not just at the end of the year.

The timing matters.

When does funding become necessary?

Knowing that a business may require additional funding is useful.

Knowing approximately when that requirement may emerge is much more useful.

A model should help management understand whether the planned cash balance stays comfortable, becomes tight or moves below an acceptable level under the assumptions being tested.

That information can materially change the timing of a business decision.

What happens if things go better than expected?

Scenario analysis should not only be about downside risk.

An expansion that performs better than expected can also require additional working capital, inventory, staff or capacity.

Higher revenue can create its own funding requirement.

That is why an expansion scenario should test the full financial consequence rather than changing only the sales line.

What happens if things take longer?

This is often where a model becomes most useful.

What if customers take longer to come in?

What if pricing needs to be lower?

What if costs are higher?

What if the new location or business line takes six additional months to reach the planned level?

A conservative scenario does not mean assuming disaster.

It means asking what happens if reality is less convenient than the base plan.

Which assumptions deserve the most attention?

Not every assumption needs the same level of debate.

If changing one assumption by 5% hardly affects the result, management may not need to spend hours perfecting it.

If a small change in another assumption creates a major cash shortfall, that assumption deserves much more attention.

That is the value of sensitivity analysis.

It tells management where uncertainty actually matters.

The output should help someone make a decision

A financial model should eventually help management say something useful.

For example:

We can make the investment without additional borrowing if collections remain within this range.

We can expand, but the working-capital requirement appears six months earlier than expected.

The project remains viable under the conservative scenario, but we need a larger cash buffer.

The decision only works if this particular margin assumption is achieved.

Those conclusions are more valuable than a spreadsheet containing thousands of formulas.

Accounting tells us a great deal about what has already happened.

A useful financial model takes that information, adds assumptions about what could happen next and gives management a way to test the consequences before committing to the decision.

That is the purpose of the model.

You can read more about Financial Modelling for business decisions.