Side Hustle Admin: The HMRC Checklist Most New Freelancers Miss

Whether you are selling handmade goods on a marketplace platform, offering freelance design or writing services, renting out a room, driving for a delivery platform, or running a small online business alongside your day job — the moment your earnings outside employment exceed certain thresholds, HMRC expects action. Many people either do not know this, or know it vaguely but find the administrative requirements unclear enough to put off indefinitely.

The consequences of getting it wrong are genuinely unpleasant: late filing penalties, interest on unpaid tax, and in serious cases formal investigations. The good news is that the requirements are manageable if approached methodically.

The Trading Allowance: The First Threshold to Know

The trading allowance is £1,000 per tax year. If your total gross income from self-employment (or selling goods and services, including online platforms) is below £1,000 in a tax year, you do not need to register for Self Assessment or pay tax on that income.

This is a gross figure — not your profit after costs. If you earned £950 selling items at craft fairs, the trading allowance covers you entirely. If you earned £1,100, the entire amount becomes reportable (though you can deduct either the trading allowance or your actual costs — whichever is more beneficial).

The trading allowance is separate from employment income and the personal allowance. You can earn up to £12,570 from employment before paying income tax on that income regardless of what you earn from a side hustle.

When You Must Register for Self Assessment

You need to register for Self Assessment and file a tax return if, in any tax year (6 April to 5 April the following year):

• Your self-employment income exceeds £1,000 (the trading allowance threshold)
• You earn income from renting out property
• You have income from savings, investments or dividends above the relevant allowances
• Your total income (including employment) exceeds £100,000
• You receive Child Benefit and you or your partner earns over £60,000

Registration for Self Assessment must be done by 5 October following the end of the tax year in which you started earning. So if you began your side hustle in the 2025-26 tax year (which ends 5 April 2026), you need to register by 5 October 2026.

Record Keeping: The Basics

HMRC requires you to keep records of your self-employment income and expenses for at least five years after the relevant tax return filing deadline. In practice, this means:

• All invoices you issue to clients or customers
• Receipts or records for every business expense you claim
• Bank statements for any business account (and personal account entries related to the business)
• Records of any cash transactions

A spreadsheet is sufficient — HMRC does not require specialist accounting software for simple self-employment. However, free tools like Wave, QuickFile or low-cost options like FreeAgent (free with some business bank accounts) make the process considerably easier.

Allowable Expenses

You can deduct genuine business expenses from your self-employment income before calculating the profit on which tax is due. Common allowable expenses include:

• Materials and stock used to produce goods you sell
• Professional fees (accountant, solicitor) related to the business
• Subscriptions to relevant professional bodies or software
• Business travel (not commuting) — mileage at HMRC approved rates, or actual cost
• A proportion of home costs if you use part of your home for work (home working flat rate or actual cost calculation)
• Marketing and advertising costs

Personal expenses with a business element — such as a phone used for both personal and work calls — can generally be claimed on a proportionate basis.

National Insurance

Self-employed individuals pay Class 4 National Insurance on profits above the relevant threshold (£12,570 in 2025-26), currently at 6%. Class 2 NIC was effectively abolished from April 2024, so most self-employed people below the Class 4 threshold have no NIC liability on side hustle income — but check the current HMRC guidance as rates and thresholds are updated annually.

HMRC's helpline (0300 200 3310) is genuinely helpful for straightforward queries, and the HMRC website has a comprehensive Self Assessment guide. If your income or expenses are at all complicated — rental income with mortgage interest, for example, or significant capital equipment purchases — an accountant for the first year is likely to pay for itself.