Overly optimistic forecasts, underestimated costs, no financial reserve — find out what mistakes founders most often make when creating a business plan and how to avoid them.
A business plan is one of the first documents that takes shape in every entrepreneur's mind. The problem is that business reality rarely matches the spreadsheet filled in during enthusiastic evenings before a company launches. Underestimated costs, overestimated revenues and a lack of cash reserves are the three most common reasons why promising ventures fail before the end of their first year. In this article we show you how to prepare a realistic budget, what pitfalls to avoid and why working with an accounting firm as early as the planning stage can save your business.
Founders are naturally optimistic thinkers — a trait that drives action, but one that can be dangerous when planning finances. The most common mistake is the so-called planning fallacy: we assume everything will go according to schedule, clients will appear quickly and costs will remain stable. In practice, however: • first revenues arrive on average 2–3 months later than planned, • fixed costs grow as the business scales (legal services, accounting, licences), • unexpected expenses — breakdowns, complaints, regulatory changes — are the rule, not the exception. A good business plan is not a document written once for the bank. It is a living tool that is reviewed every quarter.
Realistic financial forecasting starts with costs, not revenues. Gather all expenditures in three categories: 1. One-off costs (start-up): company registration, equipment, website, initial stock. 2. Fixed costs (monthly): ZUS contributions, rent, software, accounting services, salaries. 3. Variable costs: raw materials, commissions, logistics — proportional to sales. Only once you know the total of your fixed costs can you calculate the break-even point: how much you need to sell to cover your expenses. Plan revenues in three scenarios — pessimistic, base and optimistic — and manage the company according to the base scenario while always keeping a Plan B for the pessimistic one.
Based on conversations with clients from the SME sector, a recurring set of mistakes emerges: • Omitting the owner's own salary — the owner's work has a real cost that must not be ignored. • Underestimating the time to first sale — often 3–6 months without revenue while fixed costs continue. • No cash buffer — a minimum of 3 months of fixed costs should be held as a reserve. • Confusing profit with cash — a company can be profitable on paper while simultaneously facing a liquidity problem if clients pay late. • Failing to account for taxes and contributions — in 2026, the health insurance contribution, VAT and income tax advance payments are significant burdens that must be included in the budget. Each of these mistakes individually represents a serious risk. Together, they can mean the end of the business.
2026 brings a number of regulatory changes that directly affect cost planning for business operations. Whether you are setting up a sp. z o.o. or running a sole tradership (JDG), you must account for: • The health insurance contribution — its amount depends on the form of taxation and income level, and an incorrect estimate can disrupt cash flows. • Mandatory KSeF (Krajowy System e-Faktur) — requires adapting invoicing processes and potentially implementing new software. • JPK_CIT and JPK_PKPIR — new reporting obligations for CIT taxpayers and those maintaining a KPiR. The implementation costs of these requirements (software, training, time) should appear in the budget at the planning stage, not only when a deadline is approaching.
Preparing a business plan independently is possible, but it carries the risk of confirmation bias — we see in the numbers what we want to see. An external expert — a financial adviser or an experienced accounting firm — looks at the project without emotional involvement and often identifies: • unrealistic margins relative to the market, • overlooked cost categories, • incorrect assumptions regarding the form of taxation, • a legal structure mismatched to the planned scale of operations. Working with an accounting firm before registering the company allows you to choose the optimal form of taxation, plan salary payments and avoid the first costly tax mistakes.
A business plan does not end its role on the day the company is registered. Good practice includes: 1. Monthly comparison of the budget against actual revenues and costs (variance analysis). 2. Quarterly update of forecasts for the next 12 months (rolling forecast). 3. Annual review of strategic assumptions — does the business model still make sense? The tool for ongoing verification is well-maintained accounting records with management reports. If your accounting firm delivers only tax declarations and not data for business decisions — it may be worth reconsidering your approach. The figures from the accounting books are the most valuable source of information about the company's financial health.
A realistic business plan is the foundation of a sustainable business — not a document written for the bank, but a tool for day-to-day management. If you are planning to start a company or want to verify whether your financial forecasts are grounded in reality, contact the Danexis team. Our specialists will help you assess your budget, select the appropriate form of taxation and ensure compliance with current regulations. Write to us at kontakt@danexis.pl or call: +48 780 760 666.