What it means
Every forecast rests on a handful of drivers, typically growth rate, pricing, margin, headcount and capital spending. The base case fixes a defensible value for each of these, and the scenarios around it change one or several to test how sensitive the answer really is.
The discipline matters because a base case anchors decisions long after the spreadsheet is built. Loan covenants, hiring plans, bonus targets and valuation multiples all get set against it, so an optimistic base case quietly commits the business to obligations it may not be able to meet.
In practice the most common failure is that the base case is really an upside case wearing a different label. If a business has grown 6% a year for three years and the base case assumes 20%, that is a stretch target, not a central expectation, and every downside scenario built from it will still be too generous.
Good practice is to write the assumption behind each driver next to the number, with the evidence for it. "Revenue growth 8%, based on the last four quarters averaging 7.5% and one signed contract adding roughly 1%" is a base case someone can challenge, whereas an unexplained 8% is just a number in a cell.
The base case is also the thing you should revisit rather than defend. Comparing actual results against it every quarter shows which assumptions were wrong and by how much, which improves the next forecast far more than arguing about whether the original plan was achievable.
In practice
Real-world examples.
Example
A software company preparing a funding round builds a base case at 40% growth, an upside at 60% and a downside at 20%. The investor prices the round off the base case and writes milestones against it, so the founders resist the temptation to inflate it.
Example
A manufacturer's board approves capital spending of $4 million only if the project pays back within four years in the base case. Testing the downside shows payback stretching to seven years, so the board stages the investment in two phases instead.
Example
A retail chain reviews its base case each quarter against actual trading. After three quarters of footfall running 5% below assumption, it revises the base case down rather than leaving the original plan in place and calling the gap a timing issue.
Think of it
“The base case is your best guess scenario-what you think will most likely happen.
Formula
Calculation
Base case value = prior period actual x (1 + expected growth rate), with each further line built from its own documented assumption.
A business closed last year with revenue of $10,000,000 and an EBITDA margin (earnings before interest, tax, depreciation and amortisation, expressed as a percentage of revenue) of 21%. The base case assumes 8% revenue growth and a margin of 22% as scale improves.
Base case revenue is $10,000,000 x 1.08 = $10,800,000, and base case EBITDA is $10,800,000 x 0.22 = $2,376,000.
The upside case assumes 14% growth and a 25% margin: $10,000,000 x 1.14 = $11,400,000 of revenue and $11,400,000 x 0.25 = $2,850,000 of EBITDA. The downside case assumes 2% growth and an 18% margin: $10,000,000 x 1.02 = $10,200,000 of revenue and $10,200,000 x 0.18 = $1,836,000 of EBITDA.
The spread from $1,836,000 to $2,850,000 is $1,014,000, which is 42.7% of the base case EBITDA. That range, not the single base case number, is what a lender setting a covenant or a board approving a hiring plan should be looking at.Case study
Seen in the real world.
This is an illustrative and entirely fictional case. Latchford Home Systems, an invented installer of heating equipment, built its annual plan on a base case of 18% revenue growth, drawn from one exceptional year in which a government grant scheme had briefly doubled demand.
On the strength of that base case the fictional company hired 40 additional installers, leased two extra depots on five year terms, and agreed a bank facility with a covenant tied to earnings. Actual growth came in at 4% once the grant scheme closed, and the fixed cost base built for 18% growth pushed the business into a covenant breach within nine months.
In the restructuring that followed, Latchford's finance team rebuilt the model with a base case anchored to a three year average excluding the grant year, and required every driver to carry a written justification. The following year's plan was far less exciting, and it was met, which allowed the company to renegotiate its facility on better terms.
Watch out
Common mistakes.
- Building a base case from the best year the business has ever had, which turns a stretch target into the number everyone plans and borrows against.
- Leaving assumptions undocumented, so nobody reviewing the model can tell whether an 8% growth rate came from analysis or from optimism.
- Treating the base case as fixed for the year, rather than revising it as actual results reveal which assumptions were wrong.
Questions
People also ask.
How is a base case different from a budget?
A base case is the expected outcome used for analysis and valuation, while a budget is a commitment used to control spending, and the two are often deliberately set at slightly different levels.
How far should the downside case sit below the base case?
Far enough to represent a genuinely bad but plausible year, which for most businesses means testing a stall in growth and a margin squeeze at the same time rather than one at a time.
Who should sign off the base case?
The management team owns it, but it carries far more weight when the assumptions have been challenged by someone with no stake in the outcome, such as a non-executive director or an external adviser.
From the founder's library
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