Being a contractor comes with freedom and flexibility, you’re your own boss, choosing the projects you work on and when you work. But along with that independence comes responsibility, and one of the biggest is filing your Self-Assessment tax return with HMRC.
Unlike employees who pay tax through PAYE, contractors must report their income and expenses directly to HMRC and pay any tax owed themselves. Miss a deadline, and you could face penalties, interest charges, and unnecessary stress.
The good news? Staying compliant doesn’t have to be complicated, as long as you know the key deadlines and plan ahead.
Why Self-Assessment Matters for Contractors
If you earn money outside of PAYE, whether you’re a limited company director, sole trader, or CIS (Construction Industry Scheme) contractor—you’re responsible for telling HMRC how much you earned and what expenses you’ve claimed.
Self-Assessment ensures:
You pay the right amount of tax and National Insurance
You claim all legitimate business expenses (reducing your tax bill)
You avoid penalties and investigations from HMRC
In short: staying on top of your Self-Assessment is part of being a smart, financially secure contractor.
The Key Self-Assessment Deadlines
Here are the dates every contractor should have in their calendar:
5 October – Deadline to register for Self-Assessment (if you’ve never submitted before)
31 October – Paper tax return deadline (most contractors file online, so this may not apply)
31 January – Online tax return deadline + first tax payment due
31 July – Second payment on account due (if applicable)
Miss them, and HMRC doesn’t mess around:
£100 penalty immediately if you’re late with your return
Daily penalties if you’re more than 3 months late
Interest charges on unpaid tax
Tips to Stay Ahead of Deadlines
Keep records in real time – Track invoices, receipts, and expenses as you go. Don’t wait until January to panic.
Set money aside – Aim to save 20–30% of each payment you receive for tax. That way, your bill won’t feel like a shock.
Use digital tools – HMRC is rolling out Making Tax Digital (MTD). Accounting software like QuickBooks, Xero, or FreeAgent makes compliance easier.
Plan for payments on account – Many contractors forget this. If your bill is over £1,000, you may need to make advance payments for the following year.
Get professional help – An accountant can save you money by ensuring you claim everything you’re entitled to.
What If You Miss a Deadline?
Life happens, and sometimes deadlines get missed. If you’re late:
File as soon as possible to limit penalties.
Contact HMRC if you have a genuine reason they may reduce fines.
Set reminders so it doesn’t happen again.
Remember: the longer you wait, the more expensive it gets.
Final Thoughts
For contractors, Self-Assessment deadlines aren’t just dates on a calendar, they’re financial guardrails that keep your business on track. Missing them can cost you money, stress, and even your reputation.
By staying organised, using digital tools, and planning ahead, you’ll make tax season a lot less painful, and avoid giving HMRC more than they deserve.
