HMRC is about to charge you £10/day. Yes, really.

If you filed your self-assessment tax return late (or, you know, haven't filed it yet), you might want to sit down.

As of 1 March 2026, HMRC started charging £10 per day in penalties. On top of the £100 you already owe. Every single day until you file.

Quick maths:

• Filed 1 week late in Feb? £100. Annoying but fine.
• Still haven't filed by mid-March? £100 + (14 × £10) = £240.
• Leave it to May? £100 + (90 × £10) = £1,000.
• Then the 6-month penalty kicks in. And the 12-month one.

The bit nobody tells you

You can file with estimated figures and amend later.

Seriously. HMRC would rather have a roughly-right return today than a perfect one in June. Filing stops the daily penalty clock immediately.

"But I don't have my exact numbers—"

Doesn't matter. Check your bank statements. Estimate your expenses conservatively. File. Amend when you have the real figures. The return stops the bleeding.

What counts as a reasonable excuse

• Serious illness or hospital stay ✅
• Bereavement ✅
• HMRC's own website being down ✅
• "I forgot" ❌
• "I was busy" ❌
• "I didn't have the money" ❌ (you can file without paying)

If you have a genuine excuse, here's how to appeal.

Tools that might help

I built a penalty calculator that shows you exactly what you owe based on how late you are. Also a live penalty counter that updates in real-time. Both free, no sign-up.

If you can't pay the bill, HMRC offers Time to Pay arrangements — basically a payment plan. They're surprisingly reasonable about it if you call before they chase you.

TL;DR

File today. Estimate if you have to. Stop the £10/day clock. Sort the details later.

Anyone else dealing with this right now? Curious how many devs here do self-assessment vs. PAYE.