Do I Need to Register as Self-Employed to Sell on Whatnot?

If you sell on Whatnot, whether as a side hustle or a full-time business, you may need to register as self-employed with HMRC.

The short answer is: if you are buying items to resell, running regular shows, and your total trading income is more than £1,000 in a tax year, you probably need to register for Self Assessment.

This guide explains the £1,000 trading allowance, when selling personal items is different, how to register, what happens if you miss the deadline, and what records Whatnot sellers should keep from day one.

When Do You Need to Register?

In the UK, you need to tell HMRC about self-employed income if you are trading and your total trading income is above the relevant threshold. This includes income from Whatnot and other online platforms.

The £1,000 trading allowance

If your total trading income is £1,000 or less in a tax year, you may be covered by the trading allowance. That means you may not need to register for Self Assessment for that income.

The important part is that the £1,000 is based on income before expenses, not profit. If you sell £1,200 of items and spent £900 buying stock, your income is still over £1,000, even though your profit is only £300.

If you earn over £1,000

Once your trading income is over £1,000 in a tax year, you usually need to:

1. Register for Self Assessment with HMRC.
2. Declare your Whatnot income and expenses.
3. File a Self Assessment tax return each year.
4. Pay Income Tax and, where relevant, National Insurance on your profit.

You may still need to file even if your profit is below the Personal Allowance, because HMRC needs the return to calculate the position properly.

When Should You Register?

You should register for Self Assessment by 5 October after the end of the tax year in which you first needed to file a tax return.

For example:

• You start trading on Whatnot in September 2026.
• Your trading income goes over £1,000 before 5 April 2027.
• You should register by 5 October 2027.
• Your online tax return and tax payment will usually be due by 31 January 2028.

HMRC explains the process on its Self Assessment registration page.

What If You Are Already Employed?

You can be employed and self-employed at the same time. Many Whatnot sellers have a day job and run shows in the evenings or at weekends.

Your employer deals with PAYE on your wages, but that does not cover your Whatnot income. If your Whatnot selling is a trade and your total trading income is above £1,000, you still need to register and declare it through Self Assessment.

Selling Personal Items vs Trading

Not every sale on Whatnot is automatically a business. If you are genuinely selling your own personal possessions, such as old clothes, collectibles or household items, HMRC may not treat that as trading for Income Tax.

HMRC's guidance on selling through online platforms explains that selling personal possessions is different from selling goods as a trade.

Signs you may be trading

• You buy items specifically to resell.
• You run regular live shows.
• You sell similar items repeatedly.
• You make consistent profits.
• You have branding, stock records or a business bank account.
• You sell across Whatnot and other platforms.

Signs it may be a clear-out

• You are selling items you personally owned and used.
• You are not buying replacement stock to resell.
• Sales are occasional rather than regular.
• You are not trying to build a business or make repeat profits.

If you sell a personal possession for more than £6,000, Capital Gains Tax can sometimes be relevant. HMRC has separate guidance on Capital Gains Tax on personal possessions.

What Happens If You Do Not Register?

If you register late and do not pay all tax due by 31 January, HMRC may charge a failure to notify penalty. The penalty depends on the tax unpaid and the circumstances.

If your tax return itself is late, HMRC can charge late filing penalties, including an initial £100 penalty, daily penalties after 3 months, and further penalties at 6 and 12 months. Late payment interest and penalties can also apply.

HMRC explains these rules on its Self Assessment penalties page.

How to Register as Self-Employed

Registering is done through GOV.UK. You will usually need:

• Your National Insurance number.
• Your personal details and address.
• The date you started trading.
• A description of your trade, such as “online reseller” or “online retail”.
• Your business name, if you use one.

HMRC will issue a Unique Taxpayer Reference, usually called a UTR. Keep this safe because you use it for Self Assessment.

What About National Insurance?

Self-employed sellers may pay National Insurance on profits. For 2026/27, Class 4 National Insurance is due on profits above £12,570 at 6% up to £50,270, then 2% above that.

Class 2 National Insurance is generally treated as paid for eligible self-employed people with profits above the small profits threshold, helping protect your National Insurance record. If your profits are low, you may be able to pay voluntary Class 2 contributions to protect entitlement to certain benefits and State Pension.

Check the current rules on HMRC's self-employed National Insurance page.

Do You Need a Business Bank Account?

If you are a sole trader, you are not legally required to have a separate business bank account. But for Whatnot sellers, it is strongly recommended.

A separate account helps you:

• Track Whatnot payouts clearly.
• Keep stock purchases separate from personal spending.
• Reconcile platform fees, postage and refunds.
• Prepare your Self Assessment faster.
• Build cleaner records if you apply for a mortgage or business finance.

What Records Should Whatnot Sellers Keep?

Good records make it easier to claim the right expenses and avoid overpaying tax. Cloud bookkeeping can help once sales become regular.

Do You Need an Accountant?

You do not legally need an accountant to register as self-employed or file a tax return. But an accountant can be useful if you sell regularly, hold stock, sell across platforms, or are unsure what you can claim.

An accountant can help you:

• Register correctly with HMRC.
• Claim allowable expenses such as stock, postage, packaging and platform fees.
• Set up simple bookkeeping.
• Monitor VAT registration thresholds.
• Decide when a limited company might make sense.
• File your Self Assessment accurately and on time.

Key Takeaways

• You probably need to register if you are trading on Whatnot and total trading income is over £1,000 in a tax year.
• The £1,000 trading allowance is based on income before expenses.
• Register by 5 October after the end of the tax year in which you first needed to file.
• You can have a job and still be self-employed for Whatnot income.
• Selling personal possessions is different from buying stock to resell.
• Keep proper income and expense records from day one.

Need Help Getting Set Up?

At Simplr Accounting, we help Whatnot sellers get their tax affairs sorted from day one, including registration, bookkeeping, Self Assessment and VAT planning.

If you are not sure whether you need to register, book a free discovery call and we will talk you through it.