Becoming self-employed is exciting but the admin that comes with it can feel confusing, especially if you’re used to PAYE. HMRC requires every self-employed person to register, get a Unique Taxpayer Reference (UTR), and submit a Self Assessment tax return each year.
Yet many people accidentally delay, mis-register, or overlook important steps without realising it. These mistakes are common among tradespeople, gig workers, freelancers, CIS subcontractors, and anyone earning “side income” for the first time.
This guide highlights the mistakes new self-employed workers make with their UTR number and how to avoid them so you stay compliant and avoid unnecessary stress later in the year.
Mistake 1: Confusing PAYE work with Self-Employed Income
Many people think that if they already have a PAYE job, they don’t need a UTR for their extra income.
But HMRC treats every pound earned outside PAYE as self-employment.
That includes:
- gig economy delivery
- freelance work
- contracting
- selling goods or services
- part-time construction/CIS work
- side jobs like cleaning, hair, tutoring or repairs
Once you earn more than £1,000 a year from this kind of work, you must register as self-employed. You’ll then receive a UTR and will be expected to file a Self Assessment each year.
Mistake 2: Using the wrong address or moving before the letter arrives
Your UTR is sent by post, which creates problems for anyone who:
- lives in shared accommodation
- moves frequently
- uses a temporary address
- updates HMRC late
- submits mismatched address details
If the letter is returned or lost, your UTR is delayed and your tax return can’t be filed.
Tip: Use your most stable address, not always your current one and make sure it matches HMRC records.
Mistake 3: Entering the wrong “Start Date” when registering
HMRC asks for the date you became self-employed and this is where many registrations go wrong.
People often enter:
- the date they thought about starting
- the date they bought tools
- the date they left a PAYE job
When HMRC wants the date you actually earned your first self-employed income.
Wrong dates can cause:
- incorrect tax-year obligations
- unexpected penalty letters
- duplicate UTR registrations
If you’re unsure, it’s better to register from the nearest realistic date rather than guessing.
Mistake 4: CIS workers registering for CIS before getting a UTR
If you work in construction, electrical, plumbing, labouring or site-based trades, you’ll likely fall under the Construction Industry Scheme (CIS). A lot of subcontractors try to start with CIS registration first but HMRC requires a UTR before you can join CIS.
Without it:
- contractors deduct 30% tax
- verification fails
- you lose cashflow
- tax refunds are harder to calculate
Mistake 5: Forgetting that a Self Assessment must be filed every year
Once you receive a UTR, HMRC expects you to submit a Self Assessment tax return every single year, even if:
- you had low income
- you only worked for a short period
- you didn’t make a profit
- you also worked PAYE
- you stopped trading partway through the year
Missing a tax return triggers late filing penalties automatically.
Mistake 6: Not keeping track of Income, Expenses or Statements
New self-employed workers often start the year with good intentions but quickly lose track of:
- invoices
- CIS statements
- receipts
- mileage
- expenses
- app/platform downloads (Uber Eats, Amazon Flex etc.)
This makes your Self Assessment harder and usually results in higher tax than necessary because you can’t claim everything you’re entitled to. Simple logs are better than nothing. Bank statements work fine too.
Mistake 7: Assuming HMRC automatically calculates everything for you
Many people think HMRC receives all the information from:
- delivery apps
- contractors
- gig platforms
- agencies
- invoicing tools
But HMRC does not calculate your tax automatically when you’re self-employed. You must report your own income and expenses through the Self Assessment return. If you miss information or report it incorrectly, HMRC will send underpayment letters, sometimes months later.
A better way to get your UTR right from the start
Becoming self-employed shouldn’t feel overwhelming. If you avoid these early mistakes, the entire process becomes much smoother:
- register on time
- use a stable address
- know your correct start date
- track your income and expenses
- understand whether CIS applies
- submit your Self Assessment early
- keep your UTR safe for all future tax years
The more organised your first year is, the easier every year after becomes. For many workers, the biggest change is simply understanding that HMRC sees them as self-employed even if they only deliver on weekends or pick up the occasional trade job.
FAQs
- Do I need a UTR if I earn under £12,570?
Yes, HMRC requires registration if you earn more than £1,000 self-employed income, even if your total income stays below the tax-free threshold.
- Can I have a UTR while still working a PAYE job?
Yes. PAYE and self-employment run alongside each other.
- What if I forget to file my Self Assessment?
HMRC issues automatic penalties, even if you had no profit or only worked part of the year.
- Can HMRC issue more than one UTR?
No, you should only ever have one UTR for life.
Ready to Register for Your UTR?
Whether you’re in trades, delivery, freelancing, gig work or starting out for the first time, registering early prevents penalties and ensures you’re set up properly from day one.