“Write a business plan” sounds like homework, and for years that’s exactly how it was treated: a thick binder of projections nobody read before a bank loan got approved. But the real purpose of a business plan is less about the document and more about the thinking it forces you to do — and that thinking looks very different depending on what you’re actually trying to accomplish.
How to Write a Business Plan: Start By Picking the Right Format
The U.S. Small Business Administration recommends choosing between two formats based on your goals. A traditional business plan is a detailed, multi-page document built around nine core sections: an executive summary, company description, market analysis, organization and management structure, service or product line description, marketing and sales strategy, and funding requests with financial projections. It suits entrepreneurs who want comprehensive documentation, are meticulous planners, or need to satisfy a conventional lender’s underwriting process.
Or Go Lean
The alternative is a lean startup plan, which the SBA describes as typically fitting on a single page and taking about an hour to draft. Rather than narrative sections, it maps out partnerships, activities, and resources; value propositions; customer experience, target market, and channels; and cost structure alongside potential revenue streams. It’s built for founders with simple business models, or anyone who expects to pivot quickly and doesn’t want a hundred-page document standing in the way. The SBA is explicit that neither format is objectively “correct” — the right choice depends on your business and your audience.
Answer Four Questions, Not Just Fill In Sections
In a widely cited Harvard Business Review piece, Harvard Business School professor William Sahlman argued that a genuinely useful business plan evaluates four interdependent factors, regardless of format. The people: what do the founders know, whom do they know, and how well are they known and regarded? The opportunity: is the market large or rapidly growing, and is the industry structurally attractive? The context: do the founders understand the regulatory, economic, and competitive environment they’re operating in, and how they’ll respond when it shifts? And risk and reward: does the plan honestly identify what could go wrong, and realistically size the potential payoff and timeline?
Don’t Drown in Financial Projections
Sahlman’s sharpest point may be his warning about spreadsheets. “Every seasoned investor knows that detailed financial projections for a new company are an act of imagination,” he wrote, arguing that too many plans bury genuinely useful information under pages of speculative five-year forecasts. Investors and lenders generally know those numbers will be wrong; what they’re actually evaluating is whether the founders understand their own assumptions and can reason clearly about the business. A shorter plan that shows sharp thinking about the four factors above tends to serve a founder better than a longer one padded with false precision.
Treat It as a Living Document
Whichever format you choose, the biggest mistake is writing a business plan once and filing it away. Sahlman noted that composing a great plan is hard partly because “most entrepreneurs are wild-eyed optimists,” which makes brutal honesty about risk difficult but essential. The SBA likewise frames business planning as an ongoing exercise: a document to revisit as the market, the team, and the numbers change, not a one-time certificate you earn before opening your doors.