If you're self-employed in the UK, you have a relationship with HMRC whether you like it or not. And HMRC has a very simple rule: pay on time, or pay more.
The deadlines you need to know
5 October: Register for self-assessment (if you haven't already).
31 October: Deadline for paper tax returns.
31 January: Online tax return deadline AND first payment on account for the next tax year.
31 July: Second payment on account.
Miss any of these and you're looking at automatic penalties. The 31 January deadline alone carries an immediate £100 fine for being even one day late, plus interest on anything owed.
Payments on account catch people out
Many self-employed people don't realise they need to make two advance payments each year — in January and July — based on the previous year's tax bill. These aren't optional. Forgetting the July payment is one of the most common self-employed tax mistakes.
Set it once, never miss it
Add each deadline to again as a one-off or annual task. "TAX RETURN" due January 31st. "PAYMENT ON ACCOUNT" due July 31st. You'll get a text on the day — or a few days before if you set it up that way. Reply DONE when it's filed or paid.
It's the cheapest insurance against late payment penalties you'll ever have.