If you’re worried because you can’t pay your tax bill in full, you’re not alone. This is one of the most common questions HMRC hears every year: what happens if I file my Self Assessment but can’t pay?
Here’s the key point many people miss. HMRC treats late filing and late payment as two separate issues. One triggers penalties quickly. The other is usually more flexible.
Let’s break it down so you know exactly where you stand and what to do next.
Late Self Assessment filing: where penalties start fast
If your Self Assessment tax return is filed after the deadline, HMRC applies penalties automatically. These apply even if you owe very little tax or nothing at all.
The £100 fixed penalty
As soon as your return is late, HMRC issues a £100 penalty.
This applies whether:
- You owe tax
- You’re due a refund
- You plan to pay later
This penalty is about the return itself, not the money.
Ongoing penalties for continued delay
If the return remains outstanding:
- After 3 months: daily penalties of £10 per day, up to £900
- After 6 months: an extra 5% of the tax due or £300 (whichever is higher)
- After 12 months: another 5% or £300 penalty
These penalties stack up quickly and are hard to reverse.
If you’re at risk of missing the deadline, using a Self Assessment filing service can stop penalties escalating.
Late tax payment: treated differently by HMRC
Late payment is not ideal, but HMRC generally views it as less serious than failing to file.
If you file your return on time but don’t pay the full tax due, HMRC does not issue an immediate fixed penalty.
Instead, you’ll usually face:
Interest on unpaid tax
HMRC charges daily interest on any unpaid balance from the payment deadline until it’s cleared. Interest continues to accrue, but it’s often far less costly than late-filing penalties.
Late payment penalties (only after time passes)
Late payment penalties typically apply:
- 5% of the unpaid tax after 30 days
- Another 5% after 6 months
- A further 5% after 12 months
These penalties can often be reduced or avoided if you act early.
Filing but not paying is usually the better option
If you’re choosing between:
- Filing late because you can’t pay, or
- Filing on time but paying later
Filing on time is almost always the better choice.
It:
- Avoids automatic filing penalties
- Keeps HMRC communication clearer
- Gives you access to payment options
This is why advisers often say: file now, pay later.
What to do if you can’t pay your tax bill
Set up a Time to Pay arrangement
HMRC may allow you to spread your tax bill through a Time to Pay arrangement, depending on:
- How much you owe
- Your payment history
- How quickly you act
Setting this up properly matters. A failed plan can lead to enforcement action, which is why Time to Pay arrangement setup support is often helpful.
Don’t ignore HMRC letters
Ignoring HMRC doesn’t pause penalties or interest. It usually escalates the situation. Early contact shows intent and keeps options open.
Common mistakes that increase HMRC penalties
- Delaying filing because payment isn’t ready
- Missing the filing deadline while waiting for funds
- Assuming HMRC will “wait”
- Not checking the HMRC penalty overview page to understand what applies
- Setting up unrealistic payment plans
Most penalties come from delay, not dishonesty.
A simple decision guide
If you’re unsure what to do, use this:
- Return not filed yet? File immediately
- Filed but can’t pay? Explore payment options
- Already late? Stop penalties by filing now
- Received penalties? Check if they can be reduced or appealed
Progress matters more than perfection.
Final takeaway
HMRC penalises late filing far more aggressively than late payment. If you’re stuck, filing the return should be your first move, even if payment has to follow later.