Top 10 Mistakes Founders Make (and How to Avoid Them)

Most founder mistakes aren't spectacular or exotic, they're predictable, avoidable, and often expensive. This guide covers the ten most common mistakes made by new UK founders, from administrative oversights to structural errors, with practical advice on how to sidestep each one.

Why founders make avoidable mistakes

Starting a business throws you into unfamiliar territory fast. You're simultaneously trying to find clients, build a product or service, manage your finances, and navigate legal and tax obligations, often without any prior training in most of these areas. Mistakes are inevitable. But many of the most common and costly ones are easily avoided with a little forewarning.

1. Mixing personal and business finances

One of the most common mistakes made by new limited company directors is failing to keep their personal and business finances properly separated. Using a personal bank account for business transactions, paying for business expenses from a personal card without proper records, or treating company money as personal money all create serious accounting problems and can attract HMRC scrutiny.

As a limited company, the company's money is legally not your money. It belongs to the company until it's formally paid to you as salary or dividends.

Fix: Open a business bank account immediately after registering your company. Never mix funds. Record every transaction from day one. [INTERNAL LINK: do you really need a business bank account]

2. Missing the Corporation Tax registration deadline

Many new directors don't know that they must register their company for Corporation Tax with HMRC within three months of starting to trade. HMRC won't remind you, the obligation is on you to register. Missing this deadline can result in penalties, and backdated interest on any tax owed.

Fix: Register for Corporation Tax through HMRC's Government Gateway as soon as you start trading, not when you think about it later. [INTERNAL LINK: corporation tax explained]

3. Not having a shareholders' agreement with co-founders

Starting a company with a co-founder without a shareholders' agreement is one of the most avoidable yet damaging mistakes a founder can make. When everything is going well, you don't need it. When things go wrong, and in co-founder relationships, they often eventually do, not having one can destroy the company.

A shareholders' agreement covers equity splits, vesting schedules, what happens if someone leaves, decision-making rights, and IP ownership. Without it, you're relying on goodwill and verbal agreements that won't hold up in a dispute. [INTERNAL LINK: co-founders guide

Fix: Before incorporating, agree your equity split, vesting schedule, and key decision-making rules. Get them documented in a shareholders' agreement drafted by a solicitor or via a legal platform.

4. Underpricing

New founders consistently undercharge. The reasoning is usually some combination of imposter syndrome ("I'm not experienced enough to charge that"), fear of losing the client ("they'll go elsewhere if I'm too expensive"), and a focus on getting work at any cost in the early stages.

Underpricing is self-reinforcing. It attracts the most price-sensitive clients (who are often the most difficult), leaves no margin for error, and makes it impossible to invest in growth. It also signals (often incorrectly) lower quality.

Fix: Research what the market pays for equivalent work. Start higher than you're comfortable with. You can always negotiate down; it's much harder to increase prices with an existing client.

5. Spending before earning

Office space, professional photography, expensive branding, premium software subscriptions, business cards, a new laptop, there's a version of "setting up a business" that involves spending a significant amount of money before you've made any. Much of this spending is about feeling legitimate rather than actually becoming legitimate.

The businesses that survive their early years are almost always the ones that kept their cost base ruthlessly low until revenue justified it.

Fix: Distinguish between costs that enable revenue (e.g. the software you need to do your work) and costs that make you feel like a "real business" (e.g. a branded hoodie). Delay the latter until you can afford them comfortably.

6. Not understanding IR35 (if you're contracting)

If you're operating a limited company and working through contracts (particularly for a single main client) IR35 is a piece of legislation you cannot afford to ignore. If HMRC determines that your working relationship is effectively employment (you work set hours, you're controlled by the client, you have no financial risk), they may apply IR35, which means you'll pay tax broadly equivalent to an employee on income from that engagement.

Fix: If you're contracting, get an IR35 assessment done before you start. Use a specialist accountant who understands the rules. Don't assume IR35 doesn't apply to you without checking.

7. Ignoring VAT until it's too late

VAT registration is required once your taxable turnover exceeds £90,000 in any rolling 12-month period. The obligation is triggered by hitting the threshold, whether or not you've registered. Founders who hit the threshold without registering can find themselves liable for VAT they never collected from clients, on top of the sales they already made. This can be devastating for cashflow.

Fix: Track your turnover actively. If you're approaching £90,000, speak to an accountant about voluntary registration, which may actually be beneficial if your customers are VAT-registered. [INTERNAL LINK: what is VAT and do I need to register]

8. Not keeping records from day one

HMRC requires you to keep financial records for a limited company for at least six years. Many founders start proper record-keeping only when their accountant asks for them at year end, by which point receipts are lost, bank transactions are uncategorised, and hours are wasted reconstructing what happened. Cloud accounting software makes this almost effortless; not using it from the start is a costly mistake.

Fix: Set up cloud accounting software (Xero, QuickBooks, or FreeAgent are all solid options) on the day you start trading. Connect it to your business bank account. [INTERNAL LINK: accounting software guide]

9. Choosing the wrong company name

A poorly chosen company name can cause problems long after registration. Common issues include: a name that's too similar to a competitor's (risking a passing-off claim), a name that doesn't translate to an available domain, a name that's too generic to be distinctive, or a name that includes a restricted word without approval. Once registered, changing your company name is possible but disruptive.

Fix: Before finalising a name, check Companies House, conduct a trademark search, and check domain and social media availability. [INTERNAL LINK: how to choose a company name] [INTERNAL LINK: is your company name available]

10. Not verifying identity with Companies House (IDV)

Since November 2025, all company directors and persons with significant control (PSCs) must verify their identity with Companies House under new Identity Verification (IDV) requirements. Failing to complete IDV can result in Companies House annotations on your company's public record, and persistent non-compliance can lead to further action. Many founders are simply unaware this requirement exists.

Fix: If you registered a company before November 2025 and haven't verified your identity, do it now via the Companies House digital identity verification service. New companies will need to complete this at registration. [INTERNAL LINK: Companies House IDV rules explained]