The UK makes it relatively simple to start working for yourself — you can register as self-employed with HMRC online in a matter of minutes. What it does not do is explain what to keep track of once you have, or how the structure of your income will affect what you owe and when.
| Task | When to do it | Common mistake |
|---|---|---|
| HMRC self-employment registration | By 5 October after your first trading year | Leaving it until after the return deadline |
| Record-keeping | From day one, not month six | Relying on bank statements alone without notes |
| National Insurance | Class 2 and Class 4 calculated at return time | Not budgeting for it throughout the year |
| Payment on account | January and July for most filers | Treating the first payment as the only one |
What counts as allowable expenses
The general principle is that costs incurred wholly and exclusively for the purpose of your work can be deducted from your taxable income. In practice this includes things like professional subscriptions, specific equipment, software used only for work, and a proportion of home running costs if you work from home. The proportion is the tricky part — HMRC publishes flat-rate guidance that avoids the need for detailed calculations, and for most people it is the simpler route.
Six records worth keeping from the start
- A copy of every invoice you send, with the date, amount and client details.
- Receipts or digital records for every business expense you intend to claim.
- Bank statements showing income received and expenses paid from a dedicated account.
- Mileage logs if you use a personal vehicle for work purposes.
- Records of any equipment or tools purchased for work use.
- Any correspondence about disputed invoices or late payment.
Invoicing habits that prevent disputes
Late payment is one of the most common problems freelancers encounter, and it is almost always easier to address before work starts than after. A brief written agreement — even an email exchange — that confirms the fee, scope and payment terms gives you a clear basis if a dispute arises. Including your bank details, a specific due date and a clear invoice reference on every invoice reduces the delays that come from clients needing to chase internal approvals.
The second-most common issue is forgetting to set aside tax throughout the year. A working assumption of 20–30% of net income held back each month covers most situations for lower earners, though anyone approaching higher rate thresholds should take more specific advice.