For self-employed individuals and small business owners, separating personal spending from business costs is a core part of day-to-day financial admin. Getting this right helps you calculate tax on actual profits while staying aligned with HMRC requirements.
The challenge for many UK startups is that expense rules can vary depending on your business structure and the nature of your work. Whether you are a sole trader working from home or a director of a limited company, the “wholly and exclusively” test is a common standard used when deciding whether a cost is allowable.
This guide outlines common expense categories, explains how home working costs are typically calculated, and highlights a few areas where startups often make mistakes.
What counts as an allowable expense
In general, an allowable business expense is a cost incurred for business purposes. Where a cost has a dual purpose (part business, part personal), you can typically only claim the business-use element.
Common categories for self-employed expenses include:
Office costs – phone, internet, postage, stationery, software subscriptions
Travel costs – fuel, parking, train or bus fares (rules vary, especially around commuting)
Legal and financial costs – accountancy fees, solicitors for business work, professional indemnity insurance
Stock and materials – items you buy to sell on, raw materials, trade-specific equipment
Clothing (limited cases) – uniforms or protective clothing, where it genuinely applies
If you want the GOV.UK overview for self-employed allowable expenses, start here: Expenses if you’re self-employed.
Calculating home-based business costs
If you operate from home, you can usually claim a proportion of certain household costs where they relate to business use. How you calculate this depends on your circumstances and how you prefer to keep records.
Method 1: Actual costs (apportioned)
You calculate a reasonable business-use proportion based on factors such as:
Space used for business – for example, one room used as an office
Time used for business – for example, part-time vs full-time working patterns
This approach can be more suitable when home working is a major part of how you operate and you want your claim to reflect real costs. GOV.UK covers using home as an office here: Office, property and equipment expenses.
Method 2: Simplified expenses (flat rate)
If you prefer a simpler approach, HMRC offers flat-rate simplified expenses for working from home (eligibility and rates depend on hours worked). The GOV.UK guidance and monthly rates are here: Working from home – simplified expenses.
Limited company vs self-employed rules
Your business structure affects how expenses are recorded and treated.
Self-employed (sole traders) – expenses are typically deducted from income to calculate taxable profit. GOV.UK overview: Expenses if you’re self-employed.
Limited company directors – the company is a separate legal entity. The company can deduct qualifying revenue expenses when calculating taxable profit, and personal benefit rules can apply where relevant. GOV.UK guidance: Company expenses you can deduct before paying Corporation Tax.
What you typically cannot claim
Misunderstanding expense rules can cause problems later, so it helps to be cautious with common “grey area” items.
Ordinary commuting – travel between home and a regular workplace is generally not treated as an allowable expense for tax purposes (rules can vary depending on working patterns and what counts as a permanent workplace).
Client entertaining – entertaining is typically not an allowable expense for tax purposes.
Fines and penalties – parking fines and late filing penalties are not allowable business expenses.
Personal clothing – everyday clothing is not allowable, even if you only wear it for work. Uniforms and protective clothing are treated differently in some circumstances.
Simple takeaway
If your priority is maintaining clean cash flow and reducing avoidable tax admin, accurate record-keeping and correctly categorising expenses are usually more important than trying to optimise every edge case. Simplified flat rates can be more suitable when you want lower admin, while an actual-cost approach can be better aligned where home working is substantial and you want claims to reflect real usage.
If your business has complex assets, mixed personal and business use, or unusual travel patterns, professional advice can be worthwhile. The right approach depends on how you plan to run day-to-day operations and how complex your business structure becomes.
StratoWrite Custom Business Plans can include practical guidance on forecasting overheads and documenting day-to-day admin routines. Relevant Specialist Info Packs may also be available in the shop for deeper tax and compliance topics.