A credible business plan does not remove uncertainty. It makes uncertainty inspectable. A reader should be able to see which numbers come from observed performance, which come from a stated source, which are assumptions and which are still unknown.
That distinction matters more than a polished forecast. A spreadsheet can add up perfectly while the commercial logic underneath it remains fragile.
Start with the decision the plan must support
“Write a business plan” is too broad. The same business may need different plans for different decisions:
- an internal plan to decide whether to hire;
- a working plan for two founders to agree priorities;
- a lender-facing plan focused on repayment and cash;
- an investor-facing plan focused on growth, risk and use of funds.
The underlying facts should stay consistent, but the decision changes the depth and emphasis. Before drafting, write one sentence: “This plan will help this reader decide this question by this date.”
That sentence prevents the document becoming a general performance of confidence.
A worked example: the neat forecast
Consider a small service business planning a new managed offer. This is an illustrative scenario, not a claimed Stratogenic customer result.
The draft forecast says:
- 20 customers in year one;
- £1,200 monthly revenue per customer;
- 70% gross margin;
- one new employee in month four;
- break-even in month eight.
The arithmetic may be correct. The evidence status is not yet visible.
Rewrite the same forecast as a set of claims:
| Claim | Current status | What would improve it? | |---|---|---| | Customers will pay £1,200 a month | Assumption based on three exploratory calls | Ask five qualified prospects to respond to a priced offer | | Twenty customers can be won in year one | Inference from an untested pipeline conversion rate | Track stage conversion and sales-cycle length for the first ten opportunities | | Gross margin will be 70% | Estimate excluding founder delivery time | Time the first three deliveries and cost the actual tool usage | | One hire in month four is sufficient | Unknown | Model delivery capacity at low, expected and high support demand | | Break-even arrives in month eight | Derived from all assumptions above | Recalculate when price, conversion, delivery time or churn changes |
Nothing about this table makes the business less ambitious. It tells the team where the plan is most sensitive and what to learn before making a harder-to-reverse commitment.
Build three linked views
1. The commercial argument
Who has the problem, what are they doing now, why might they change, and what evidence suggests they will pay? Keep customer language separate from your interpretation of it.
2. The operating model
What has to happen to acquire, serve and retain a customer? Name the people, time, systems, dependencies and capacity constraints. Revenue without delivery capacity is not a plan. It is a queue forming off-screen.
3. The financial model
Connect price, volume, timing, cost and cash. Use ranges where the evidence does not justify a single number. Show which assumptions change the runway or funding need most sharply.
The British Business Bank's guidance asks practical questions about the market, the basis of the sales forecast, required investment, available cash, repayment or investor return, and risk. That list is useful because it pulls the financial section back into the operating reality of the business.
Use sensitivity before precision
If a plan depends on 20 customers, do not spend an afternoon refining the office-cost line while leaving conversion untested. Run a simple sensitivity check:
- What happens with 10, 15 and 20 customers?
- What happens if the sales cycle takes twice as long?
- What happens if delivery needs 30% more time?
- What happens if two customers leave after three months?
The purpose is not to predict four futures. It is to find the assumptions that deserve attention now.
A useful plan should also say what the team will do if an assumption moves. “If average delivery time exceeds 12 hours, pause new sales and revise the service boundary” is more operational than a red cell in a spreadsheet.
The next useful action
Open the forecast that currently carries the most weight. Choose the five figures most capable of changing the decision. Label each one observed, stated, independently supported, inferred, assumed or unknown. Then give the highest-consequence assumption an owner, an evidence-producing action and a review date.
The Evidence-Based Business Plan System is the related catalogue tool for joining the narrative, operating assumptions, capacity and financial model into one revisable record. Its purpose is not to make a plan look certain. It is to make the decision behind it easier to inspect and improve.
Sources and transfer limits
- British Business Bank: Reviewing your business plan — used for the practical plan questions concerning market evidence, sales forecasts, investment, cash, finance and risk. It is general business guidance, not approval of a particular forecast, funding application, tax position or investment decision.
- British Business Bank: Getting your business ready for finance — used for the distinction between a credible evidence-supported proposition and a presentation alone. It does not establish lender or investor appetite for a specific business.
Sources reviewed 7 September 2026. Financial, tax, legal and funding requirements should be checked against the live circumstances and appropriate professional guidance.