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How to Write a Business Plan (With a Fill-In Outline)

How to write a business plan that is useful, not just long: what each section is for, a fill-in outline to copy, how to do the numbers, and common mistakes.

Mythex Team · 2026-09-29 · 6 min read

To write a business plan, answer a handful of questions clearly: what problem you solve, for whom, how you'll reach them, how you'll make money, what it will cost, and what could go wrong. Write each answer as a short section, back it with research and realistic numbers, and put a one-page summary at the front. The fill-in outline below gives you the structure.

A good plan is a thinking tool first and a document second. Its job is to find the weak assumption before your money does.

Who is the plan for?

Decide the reader before you write. It changes the length and tone:

If a lender or programme gives you a template, use theirs. For investors, a deck is often read first — see how to create a pitch deck.

Do the research first

A plan written without research is a wish list. Before you write, gather:

• Customer evidence — conversations with people who have the problem. How to validate an idea covers interviews and cheap tests.
• Competitors — who serves these customers now, how they price, what their reviews complain about.
• Costs — real quotes for equipment, premises, software, insurance, and suppliers.
• Pricing evidence — what people pay for alternatives, and what your early customers will pay.
• Rules — licences, permits and regulations for your type of business. Check local rules or ask an adviser.

Keep a list of sources. When someone asks "where does that number come from?", you want an answer.

The fill-in business plan outline

Copy this outline and fill in each section in plain language. Short answers are fine; vague ones aren't.

1. Executive summary (write this last)

• The business in one sentence: We help [customer] to [outcome] by [what you do].
• The problem: [What's painful or missing today, in the customer's words].
• The solution: [Your product or service and why it's better for this customer].
• Target customer: [Who, where, how many you can realistically reach].
• Business model: [How you make money: price, frequency].
• Traction so far: [Interviews, pre-orders, pilot customers, sales — only what's real].
• What you need: [Money, partners, premises] and what it's for.

2. Problem and customer

• Who exactly has this problem? Describe one typical customer.
• How do they solve it today, and what does that cost them in time or money?
• What evidence do you have that it matters to them? [Summarise interviews, tests.]

3. Product or service

• What do you offer, specifically? [Services, products, packages.]
• What does the customer get, and how is it delivered?
• What will you not do, at least at first?

4. Market and competition

• Where are your customers (area, industry, online community)?
• Who are the main alternatives, including doing nothing or using a spreadsheet?
• Why would a customer choose you? [Price, niche, quality, speed, location, expertise.]
• Include market size only if you have a source you can cite.

5. Marketing and sales

• How will customers first hear about you? [Channels, partners, referrals.]
• What happens between first contact and payment? [Your sales steps.]
• How will you keep customers and get repeat business?
• More detail: how to write a go-to-market plan.

6. Operations

• How is the work delivered day to day? [Location, equipment, suppliers, software.]
• What must be in place before your first customer? [Registration, insurance, permits.]
• What are the key processes: taking orders or bookings, delivering, invoicing, support?

7. Team

• Who is involved and what does each person do?
• What relevant experience does each person bring?
• Which gaps will you fill with hires, freelancers, advisers or partners?

8. Financial plan

• Start-up costs: [List each item, with where the figure came from.]
• Monthly running costs: [Fixed costs such as rent, software, insurance; variable costs per sale.]
• Pricing and unit economics: [Price, cost to deliver, margin per sale.]
• Sales forecast: [Month by month for the first year, with the assumptions behind it.]
• Cash flow: [When money comes in and goes out, and the lowest point your bank balance reaches.]
• Break-even: [How many sales per month cover your costs.]
• Funding: [How much you need, from where, and when.]

9. Risks and assumptions

• List your five riskiest assumptions. [e.g. "customers will pay X", "we can get Y permits".]
• For each, how will you test it and what will you do if it's wrong?

10. Milestones

• What will you achieve in the next 3, 6 and 12 months?
• Which numbers will tell you it's working? [Customers, revenue, repeat rate.]

Appendix

• Supporting evidence: research notes, quotes, CVs, letters of intent, detailed spreadsheets.

How to do the numbers

The financial section is where most plans are weakest. Some rules:

• Build from the bottom up. Don't start from "1% of a big market". Start from how many customers you can realistically reach, how many will buy, and how often.
• Write down every assumption next to the number it drives, so readers — and you — can challenge it.
• Forecast cash, not just profit. Many businesses that are profitable on paper run out of cash because customers pay late or stock must be bought up front.
• Model a bad case. What if sales are half what you expect, or costs are higher? Can the business survive?
• Keep it in a spreadsheet you can update, and paste a summary into the plan.

If money, loans or tax are involved, an accountant or business adviser can check your model. Many regions also have free small-business support services.

Keep it short and readable

• One idea per section. Use headings so readers can skip to what they care about.
• Plain words. If a sentence would confuse a friend, rewrite it.
• Evidence over adjectives. "Twelve interviews; eight described the problem unprompted" beats "huge demand".
• Tables for numbers. Easier to read than paragraphs.
• Be honest about risks. Readers trust a plan that names its weak points.

AI writing tools can help you structure sections, cut wordiness and play devil's advocate on your assumptions. They can't supply your market facts or costs, and they sometimes produce confident-sounding numbers with no source. Check every fact yourself.

Common mistakes

• Writing the plan before talking to customers.
• Hockey-stick forecasts with no explanation of where the customers come from.
• Ignoring cash flow, especially slow payers and up-front stock.
• "No competitors." There's always an alternative, even if it's a spreadsheet or doing nothing.
• Unsourced statistics that a reader can easily question.
• Writing it once and never looking at it again. Compare actuals to the plan regularly and update it.

Turning the plan into a first test

A plan tells you what to test first; the next step is testing it. Often that means a landing page to check demand, a simple booking or order form, or a small prototype. With an AI app builder like Mythex you can describe a landing page or a small web app in plain language and publish it the same day, which makes it cheap to test an assumption from section 9 before spending on the rest. If you're weighing how to fund the business, bootstrapping vs venture capital covers the trade-offs, and how to price a SaaS product helps if your business is software.