Common mistakes sole traders make

godwin-pinto
February 20, 2026

The “Oops” Audit: Common Mistakes Sole Traders Make (And How to Stay Off HMRC’s Naughty List)

Welcome back! By now, you’re practically a pro at knowing what a sole trader is and what expenses you can claim. But even the savviest entrepreneurs can trip up.

Think of me as your financial “spotter” at the gym. I’m here to make sure you don’t drop the heavy barbell of tax compliance on your toes. Let’s look at the most common blunders sole traders make in the 2024/25 and 2025/26 tax years—and how to dodge them like a pro.

1. The “Shoebox” Syndrome (Poor Record Keeping)

We’ve all been there: a wallet full of faded thermal receipts that look like blank slips of paper by January.

The Mistake: Relying on memory or physical paper trails. If HMRC asks for proof of an expense from three years ago and you can’t provide it, they can disallow the claim and slap you with a penalty.

The Fix: Go digital. Use an app to snap photos of receipts the second you get them.

Accountant’s Fun Fact: HMRC actually accepts digital copies! You don’t need to keep the physical paper as long as the digital version is legible and shows all the details.

2. The “January Heart Attack” (Not Saving for Tax)

This is the classic “First Year” mistake. You see £3,000 hit your bank account and think, “I’m rich!” No, Dave. You are approximately 70% rich. The rest belongs to the taxman.

The Mistake: Spending your gross income and having nothing left for the bill on January 31st.

The Fix: Open a separate “Tax Pot” (a high-yield savings account is best). Transfer 25-30% of every invoice you receive into it immediately.

3. Getting Blindsided by “Payments on Account”

This is the one that makes even grown business owners cry.

The Mistake: Not realizing that if your tax bill is over £1,000, HMRC assumes you’ll earn the same next year and asks you to pay half of next year’s bill in advance.

The Real World Scenario:

If your tax bill for 24/25 is £2,000, your total payment in January 2026 will actually be £3,000 (£2,000 for last year + £1,000 toward next year).

4. Mixing Business with Pleasure (Bank Accounts)

Legally, a sole trader can use a personal bank account. But should you?

The Mistake: Using one account for your grocery shopping, Netflix, and business supplies.

The Fix: Open a dedicated business account. It makes your accounting 100x faster and ensures you don’t accidentally claim for your “business lunch” that was actually a romantic dinner for two.

5. Missing the “Failure to Notify” Deadline

Many people think they only need to tell HMRC once they’ve finished their first year.

The Mistake: Missing the 5th October registration deadline.

The Fix: If you started trading between 6th April 2024 and 5th April 2025, you must register by 5th October 2025.

6. The “Hidden” Interest: Late Payment Penalties

HMRC has significantly toughened up its penalty regime. From April 2025, the interest rate on late payments is set at the Bank of England base rate + 4%. At current rates, that’s nearly 8-9%!

The Cost of Being Late (2025/26 Rules)

Time Overdue	Penalty Applied
1 day late	£100 fixed penalty (for filing)
15 days late	3% of the tax owed
30 days late	Additional 3% (6% total)
3 months late	£10 per day (up to £900)

7. Overlooking the VAT Threshold

The Mistake: Thinking the £90,000 threshold is based on your tax year or your profit.

The Fact: It’s based on a rolling 12-month turnover (your total sales, not profit). If you hit £90,001 in any 12-month period, you have 30 days to register. If you miss it, HMRC can backdate your VAT bill, which comes straight out of your pocket!