Opening a Self-Employment Business

JMT Accountancy Guide for Start-ups and Sole Traders

Common Accounting Mistakes and How to Avoid Them

Starting a business is an exciting endeavor, but without proper setup of records, tax, cash flow, and pricing from the beginning, the financial aspects can quickly become overwhelming.

By Tomasz Putynkowski, Director of JMT Accountancy Ltd

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This blog is derived from JMT Accountancy's self-employment workshop at the University of Staffordshire, delivered by Tomasz Putynkowski. It is tailored for individuals considering starting a business, those who have recently begun trading, or those earning from a side project and need guidance on the next steps.

What This Guide Covers

• Choosing the right business structure

• Registering with HMRC and key deadlines

• Understanding Income Tax, National Insurance, and VAT

• Bookkeeping from day one

• Allowable expenses and evidence

• Making Tax Digital readiness

• Common mistakes that cost small businesses money

• A practical 7, 30, and 90-day action plan

Meet Tom

Tomasz Putynkowski is the Director of JMT Accountancy Ltd, with over 20 years of experience in bookkeeping, payroll, and SME finance. JMT supports more than 170 small and medium-sized businesses, offering specialized support for start-ups, entrepreneurs, and owner-managed businesses.

The JMT approach is practical, direct, and devoid of jargon. Effective bookkeeping is not solely about compliance; it enables business owners to identify what is successful, where cash is leaking, and what requires attention before it becomes costly.

1. A Business Starts Before It Feels Official

Many new business owners delay addressing records and tax until they feel “properly established.” This is one of the most significant early mistakes. If you offer goods or services, expect to make a profit, and take responsibility for pricing, delivery, and risk, you are already entering the business realm.

Key message: The first sale equals the first record. Do not wait until January to recall your income and costs.

From the outset, maintain evidence of sales, receipts, invoices, bank transactions, mileage, and any business-related costs. Establishing your system early simplifies understanding your profit and prevents future panic.

2. Choose the Right Starting Point

Most new founders begin as a sole trader, partnership, or limited company. Each option has distinct legal, tax, and administrative implications.

Sole Trader

Quick to start. You and the business are legally the same. You report profit through Self Assessment and are personally responsible for business debts.

Partnership

Two or more people trading together. This requires clarity on profit shares, responsibilities, decision-making, and what occurs if someone departs.

Limited Company

A separate legal entity with more administration, Companies House filings, and corporation tax responsibilities.

For many start-ups, being a sole trader is the simplest route, but simplicity does not mean absence of rules. You still need clear records, tax planning, and a system to separate business funds from personal spending.

3. Your First 30 Days Checklist

The first month is crucial for establishing habits that either protect the business or create future issues. Focus on getting the fundamentals right.

• Choose and check your business name, domain, and social media handles.

• Separate business transactions from personal spending.

• Create one place for receipts, invoices, and bank evidence.

• Set pricing that covers costs, tax, and profit, not just the job.

• Check whether you need insurance such as public liability or professional indemnity.

• Understand when you must register with HMRC and keep your UTR safe.

4. Pricing: Turnover Is Not Profit

A busy business can still struggle if the pricing is incorrect. Your price must cover more than the immediate work. It should account for direct costs, admin time, unpaid time, software, insurance, tax, and your target profit.

Simple formula: Sales - Costs - Tax pot - Time = Real income.

Underpricing causes stress even when orders are plentiful. Review your prices when costs change, when your speed improves, when your value increases, or when you realize insufficient profit is retained in the business.

5. HMRC Registration and Self Assessment Deadlines

New sole traders must understand when Self Assessment applies and when to notify HMRC. The fundamental rule is to inform HMRC by 5 October following the tax year in which a return is required.

The usual Self Assessment timeline is:

• 6 April - tax year starts.

• 5 April - tax year ends.

• 5 October - registration deadline where required.

• 31 October - paper return deadline.

• 31 January - online return and payment deadline.

• 31 July - second payment on account, if applicable.

Mark these dates in your calendar. Do not rely on memory.

6. What Taxes Might Apply?

Not every business pays every tax, but every owner must know which taxes may apply. For a self-employed individual, the most common areas are Income Tax, National Insurance, VAT, PAYE if staff are employed, pension duties if employment begins, and business rates if business premises are used.

Tax is based on profit, not turnover. Profit is your business income after allowable business expenses. That is why accurate bookkeeping is crucial: poor records can lead to incorrect profit figures, missed claims, weak evidence, and unnecessary stress.

VAT is different because it is based on taxable turnover, not profit. If taxable turnover exceeds the VAT registration threshold, or is expected to, registration may be required. VAT affects pricing, invoices, cash flow, and customer perception, so it should be monitored before the business reaches the threshold.

7. Making Tax Digital Is Coming

Making Tax Digital for Income Tax is being phased in for sole traders and landlords. The workshop highlights the staged income thresholds from April 2026 onwards.

The practical advice is simple: prepare early. Use software, maintain digital records, use clear categories, and review figures regularly. Businesses that wait until the deadline may find the transition more challenging than necessary.

8. Bookkeeping from Day One

Bookkeeping should not be deferred. Each transaction should follow a consistent process:

1. Evidence - invoice, receipt, or bank record.

2. Capture - photo, upload, or email folder.

3. Categorize - income, cost, asset, or tax.

4. Reconcile - match to the bank.

5. Review - profit, cash flow, and tax pot.

Engage in bookkeeping little and often. It becomes much more difficult when memory replaces evidence.

9. Records You Must Keep

HMRC may not request every receipt when a return is filed, but the business owner must be able to provide evidence if asked. Keep records of all sales and income, all business expenses, VAT records if registered, PAYE records if employing staff, and personal income records that affect Self Assessment.

Useful evidence includes receipts, bank statements, sales invoices, till rolls, bank slips, contracts, mileage logs, and clear notes explaining mixed-use costs. Retain records for at least five years after the 31 January submission deadline for the relevant tax year.

10. Allowable Expenses: The Core Test

An expense reduces taxable profit only when it is allowable. Consider four questions before claiming:

• Was it purchased for the business?

• Can I provide evidence?

• Is there a personal element that must be split?

• Would I still purchase it if there was no business?

Common examples include office costs, travel, uniforms, staff costs, stock, insurance, premises costs, advertising, and business-related training. For home, phone, internet, and travel costs, maintain a clear and reasonable method for separating business and personal use.

11. The 10 Accounting Mistakes We See Most Often

1. Choosing the wrong structure or relying on informal advice.

2. Mixing personal and business funds.

3. Ignoring cash flow.

4. Not saving for tax.

5. Maintaining poor documentation.

6. Committing data entry and category errors.

7. Setting prices too low.

8. Making VAT and expense claim mistakes.

9. Neglecting payroll and compliance duties when hiring help.

10. Seeking professional help too late.

12. The Biggest Mistake: Mixing Personal and Business Funds

This mistake complicates the resolution of all other errors. Personal purchases appear in the business bank feed, business subscriptions are paid from personal cards, cash withdrawals are not recorded clearly, and the owner cannot quickly ascertain their profit, cash, or tax position.

The solution is straightforward: separate accounts, clear withdrawals, regular receipt capture, and monthly bank reconciliation. This provides the business owner with a clearer view of performance and simplifies year-end accounts.

13. Cash Flow: Profit on Paper Does Not Pay Bills Today

A business can show profit but still face cash shortages. This occurs when invoices are issued but not paid, stock is purchased before money is received, tax is not saved separately, supplier bills arrive at inopportune times, or personal living costs clash with business commitments.

Practical solution: Implement a 13-week cash forecast, set clear payment terms, promptly chase overdue invoices, and maintain a separate tax fund.

14. VAT and Expense Claim Errors

VAT errors often occur because the business owner does not monitor taxable turnover, adds VAT before registration, uses the wrong VAT code, or fails to keep valid VAT invoices. Expense errors occur when costs are personal, capital, unsupported, or only partially business-related but claimed in full.

The safest practice is to verify the rule before the transaction, not after the return is due.

15. Payroll and Compliance Blind Spots

Growth entails responsibilities. Before hiring staff or regular workers, business owners should consider payroll, employment status, contracts, holiday pay, pension duties, sector-specific rules such as CIS where relevant, and records of hours, pay, expenses, and reimbursements.

Payroll errors affect people as well as numbers, so it is prudent to inquire before hiring rather than attempting to rectify issues later.

16. Your Bookkeeping Rhythm

Weekly

Upload receipts, issue invoices, chase overdue payments, and check the bank balance.

Monthly

Reconcile the bank, review profit, update the tax fund, and compare cash inflow against cash outflow.

Quarterly

Review prices, VAT and MTD readiness, major costs, goals, and sales pipeline.

At year-end, clean the records, confirm expenses, file Self Assessment, and plan for the next year. Thirty minutes a week is preferable to thirty hours in January.

Your 7, 30, and 90 Day Action Plan

Next 7 days: Choose your structure, open or organize your bank account, create a receipt folder, and draft your invoice template.

Next 30 days: Register or schedule registration, set your pricing model, choose your records system, and start a weekly review.

Next 90 days: Review profit and cash flow, evaluate your VAT direction, and decide whether to enlist bookkeeping support.

How JMT Accountancy Can Help

JMT Accountancy offers practical support for SMEs, start-ups, and growing businesses, including accounts preparation, Self Assessment, bookkeeping, monthly reporting, VAT returns, payroll, pension submissions, accounting software setup, Xero training, and process improvement.

Our objective is to provide business owners with confidence, not confusion. If you are starting out, nearing the VAT threshold, behind with records, hiring staff, or unsure about your structure, obtaining advice early can prevent costly issues later.

Contact JMT Accountancy

Tomasz PutynkowskiDirector, JMT Accountancy Ltd

Email: tp@jmtaccountancy.co.uk

Suite G45, The Old Town Hall3 Gimson StreetST4 3FF Stoke-on-Trent

This blog is general educational information and should not be used as personalised tax, legal or financial advice. Tax rules and thresholds can change. Always check current HMRC guidance or speak to a qualified adviser before filing or making business decisions.