Self-assessment is due in January. Every year, thousands of UK freelancers miss it, file wrong, or find out at 11pm on January 31st that they owe twice what they expected.
Here's how to not be that person.
The actual deadline picture
- 5 October: register for self-assessment if you're new (this year's deadline for 2024/25)
- 31 October: paper return deadline
- 31 January: online return + any tax owed
- 31 July: second payment on account (if HMRC thinks you'll owe similar amounts next year)
Most people know January 31st. Fewer know that HMRC can charge interest from that date even if you file the return on time but pay late.
What most freelancers get wrong
1. Not putting aside tax as they go
The standard advice is 25-30% aside. More accurate: use HMRC's calculation.
Quick rule of thumb for a basic rate taxpayer:
- 20% income tax on profits over £12,570
- 9% Class 4 NICs on profits between £12,570 and £50,270
- 2% on anything above that
So the effective rate on most freelance income in the £20k-£50k bracket is roughly 29%. Set that aside from every invoice you receive.
Free tool: Freelancer Tax Calculator — enter your projected income and it tells you what to reserve.
2. Missing allowable expenses
You can offset these against your taxable profit:
- Home office costs (£6/week flat rate, or actual proportion of bills)
- Phone and broadband (business proportion)
- Professional subscriptions and training
- Equipment and software
- Accountant fees (yes, the accountant's fee is deductible)
- Travel to client sites (not commuting, but client visits)
- Professional indemnity insurance
Missing even a few of these can cost you hundreds.
3. Payments on account
First time you owe over £1,000 in tax, HMRC adds "payments on account" — advance payments towards next year's bill. These are 50% of your current year's liability, paid in January and July.
First-year freelancers are often blindsided by a January bill that's 1.5x what they expected. Budget for it.
4. Not having records when HMRC asks
HMRC can ask for records up to 6 years back. "I lost the receipts" is not an acceptable response.
Use a simple spreadsheet. Log every income and expense as it happens. A basic tracker takes 15 minutes a month and saves hours of panic in January.
If you want a pre-built template: Freelancer Tax Tracker Spreadsheet — income, expenses, tax reserve, and a self-assessment checklist all in one.
The late filing penalty scale
- Up to 3 months late: £100 flat (automatic)
- 3-6 months late: £10/day up to £900
- 6-12 months late: additional £300 or 5% of tax (whichever is higher)
- Over 12 months: double penalties, potential investigation
The interest on late payment is currently 7.25% per annum. On a £3,000 bill, that's £218 a year — just for being late.
If you've already missed a deadline
File immediately. Every day you delay increases the penalty. Filing late is almost always better than not filing.
If you have a reasonable excuse (hospitalisation, bereavement, HMRC technical issues), you can appeal the automatic £100 penalty. Most others: just pay it and move on.
Landolio has free tax calculators and simple tracking templates for UK freelancers — no subscription, no fluff.
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