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Posted 23rd October 2026

John Lambiris on Why Business Forecasts Need Clearer Assumptions

A financial forecast becomes more useful when the people relying on it can understand what would need to happen for its numbers to hold. By John Lambiris A business expects revenue to grow next year. Its forecast shows higher sales, improving margins and enough cash to fund an additional hire. The spreadsheet adds up. The […]

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John Lambiris on Why Business Forecasts Need Clearer Assumptions

A financial forecast becomes more useful when the people relying on it can understand what would need to happen for its numbers to hold.

By John Lambiris

A business expects revenue to grow next year. Its forecast shows higher sales, improving margins and enough cash to fund an additional hire. The spreadsheet adds up. The more difficult question is whether the assumptions behind it add up too.

Perhaps the sales forecast depends on a contract that has not yet been signed. The margin improvement might rely on a supplier holding its prices. The hiring plan may assume that customers will pay within 30 days, even though some regularly take longer.

Each assumption could be reasonable. But until those assumptions are visible, the forecast is difficult to challenge or use with confidence.

For John Lambiris, whose writing explores accounting, finance and business analytics, this is a useful starting point for thinking about financial planning. A forecast should make it easier to understand how a business might perform, including where its expectations could prove wrong.

Separate confirmed business from expected business

Consider a hypothetical company preparing its annual sales forecast. Some revenue comes from signed contracts. Another portion comes from customers who usually renew. The remainder depends on winning new work.

Combining all three into one total can obscure how much uncertainty sits behind the figure.

A signed contract provides a different basis for planning from an early conversation with a prospective customer. Even contracted revenue may depend on delivery milestones or cancellation terms. A useful forecast keeps those distinctions visible.

I would want to understand how much of the expected revenue is already committed, how much depends on repeat business and how much requires something new to happen. That helps a manager judge which spending decisions the business can comfortably make now and which might need to wait.

It also makes later discussions more precise. If revenue falls short, the team can establish whether the problem came from delayed delivery, lower renewals or fewer new customers than expected.

Explain what is expected to change

A forecast often starts with last year’s figures and applies a percentage increase. That can be a practical first step, but it leaves an important question unanswered: what is supposed to produce the increase?

If sales are expected to rise, will the business serve more customers, charge higher prices or sell a different mix of products? Does it have the capacity to deliver the additional work? Will growth require more staff or higher spending before the revenue arrives?

These questions connect the financial model to the way the business operates.

Imagine a service business forecasting more assignments with no increase in staffing costs. That might be achievable if it has unused capacity or has improved a time-consuming process. If neither is true, the forecast needs a stronger explanation.

In my Strixus article on the hidden cost of complexity in growing businesses, I explored how additional handoffs and exceptions can consume time without appearing clearly in headline results. A forecast needs to account for that operational work, particularly when growth introduces more coordination.

An assumption becomes easier to assess when someone can describe the change behind it. “Revenue will increase by 10 per cent” gives the team a target. Explaining which customers, services or capacity changes support that increase gives them something to examine.

Keep cash timing visible

A forecast can show a profitable period while leaving the business short of cash during it.

Suppose a company takes on a substantial project. It must pay staff and suppliers while the work is underway, but the customer pays after completion. The project may generate a worthwhile margin and still create a funding gap before payment arrives.

That is why the timing of receipts and payments deserves its own attention. Recording expected revenue does not establish when the money will reach the bank account.

I would want the forecast to show the agreed payment terms, any upfront payments and the effect of a realistic delay. If the business has a history of late collections, assuming every customer pays exactly on time needs justification.

This connects with a theme in my earlier Substack article on strong financial controls: the value of reliable records. Forecasting cash becomes harder when the underlying information about invoices, collections and commitments is incomplete or out of date.

This detail matters when a forecast supports a commitment such as hiring, buying equipment or signing a lease. The business needs to understand whether it can meet those obligations throughout the period.

Test the assumptions that could change the decision

A model can contain hundreds of inputs. Examining all of them equally may consume time without improving the decision.

The more useful task is to identify the assumptions that have the greatest effect on the proposed commitment.

For a business considering an additional employee, the crucial variables might be the start date of a new contract and the volume of work it brings. For a company holding inventory, customer demand and the time taken to sell stock may matter more.

Testing those variables does not require an elaborate model. What happens if the contract begins two months later? What happens if sales are lower but supplier payments remain due?

A meaningful alternative scenario changes related assumptions together. Slower sales could also mean stock remains unsold for longer, delaying cash receipts. Reducing revenue while leaving everything else untouched may miss the practical consequences.

The purpose is to understand when the proposed decision stops being comfortable and what options remain at that point.

Make revision part of the process

Once a forecast is approved, it can become a fixed reference point even as the business changes around it.

A short record of the main assumptions helps prevent that. It can identify what each assumption is based on, who can verify it and when it should be reviewed. When new information arrives, the team can update the relevant part of the model without losing sight of the original reasoning.

Comparing actual results with expectations then becomes a learning exercise. Was the sales estimate too optimistic? Did customers pay later? Did a cost increase come from higher prices or a greater volume of work?

Those explanations make the next forecast more useful.

The test I would apply is straightforward: can someone responsible for the decision explain what needs to happen, what could change and how the business would respond?

A forecast earns its place in planning when it helps people answer those questions.

About John Lambiris

John Lambiris writes about accounting, finance and business analytics, exploring how financial information can support better business decisions. Connect with John Lambiris on LinkedIn or explore his HackerNoon profile.

Categories: Finance


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