What are business plan assumptions?
Business plan assumptions are the things you are treating as true, or likely to be true, when you build your plan, especially your financial forecasts. Because nobody knows the future, every projection rests on them. Examples include how many customers you expect, what you will charge, and how much your costs might rise.
Stating them openly lets readers see what the numbers depend on, rather than having to guess.
Why they matter
- Forecasts are only as sound as their inputs. A neat spreadsheet built on unrealistic assumptions is still unrealistic.
- Lenders and investors look at them. They often check whether the figures are reasonable and whether the reasoning is explained.
- They show what to monitor. When results differ from the plan, the assumptions point to where to look first.
- They support better decisions. Knowing which assumptions are most uncertain helps you decide what to test early.
Common types of assumptions, with examples
| Type | Example |
|---|---|
| Market | The target customer group is growing slowly; competitors will not cut prices sharply |
| Sales and pricing | We will sell a set number of units per month, at a stated price, rising gradually |
| Costs | Supplier prices stay roughly stable; rent is fixed by a lease |
| Staffing and operations | We need two employees in year one and a third when orders pass a certain level (see the operational plan) |
| Financial | Customers pay in 30 days; a loan is available at an expected interest rate |
| External | No major change in regulation or economic conditions |
The numbers should be your own, based on evidence, not copied from a template.
What makes an assumption useful
Stronger assumptions tend to be:
- Specific: “5% of website visitors will place an order” rather than “sales will be good”.
- Evidence-based: drawn from market research, quotes, past results, industry data or pilot sales.
- Consistent: the sales, staffing and cost assumptions should fit together.
- Cautious: when unsure, using more careful estimates is usually safer than optimistic ones. A risk assessment can show which assumptions are most exposed.
How to document and test them
- List them. Put the key assumptions in one table, often an appendix or beside the financial section.
- Note the source. Record where each figure came from, or label it clearly as an estimate.
- Rank by impact and uncertainty. Focus on the few that would change results the most.
- Run scenarios. Try a cautious case, an expected case and an optimistic case to see how results shift.
- Review regularly. Compare actual results to the assumptions and update the plan.
Not the same as accounting assumptions
Search results sometimes mix up two ideas. “Fundamental accounting assumptions” or concepts, such as the going concern idea (that a business will continue operating), are principles used in preparing financial statements. Business plan assumptions are your own forward-looking estimates about the market, customers and costs. A plan may mention both, but they serve different purposes.
Common mistakes
- Leaving assumptions unstated.
- Basing sales on a share of a huge market (“if we get just 1%”) without showing how.
- Ignoring how long it takes to win customers or get paid. Cash timing also drives runway.
- Never revisiting assumptions once the plan is written.
Assumptions also feed into other documents. A business case for a single project relies on them too, and they sit alongside your wider business model.