What Happens If You Miss the Self Assessment Deadline
The important thing to know is this: HMRC penalties are predictable, but they escalate quickly. You can be fined even if you owe no tax at all, and the longer the return is outstanding, the more expensive it becomes.
HMRC applies automatic penalties based on how late your return is. These charges are not discretionary and they are added whether the delay was accidental, administrative, or down to being busy.
The good news is that the system follows a clear structure. That means you can understand exactly what will happen next, what it may cost you, and what steps you can take to limit the damage.
In this post, we will walk you through:
- What penalties apply and when they start
- How interest is charged on late payments
- What to do immediately if you have missed the deadline
- How to appeal penalties if you had a genuine reason
- How to avoid the situation entirely in future years
Whether you are a first time filer, self employed, a landlord, or a company director, understanding the rules now can save you money and stress later.
For reference, you can also view HMRC’s official guidance on Self Assessment penalties here: Self Assessment late filing penalties.
1) First, which Self Assessment deadline did you miss?
Before looking at penalties or next steps, it is important to identify which deadline applies to you.
Different deadlines trigger different consequences, and confusing them is a very common reason people panic unnecessarily.
For most individuals who file their Self Assessment online, the key dates are:
- 31 October: deadline for submitting a paper tax return
- 31 January: deadline for submitting your online tax return and paying your balancing payment, plus usually the first payment on account
- 31 July: deadline for the second payment on account, where payments on account apply
Missing any of these can result in penalties, interest, or both, but the impact depends on what was due and when. For example, filing late triggers fixed penalties, while paying late can lead to interest and additional charges.
Useful official resources:
If you have missed a deadline, the most important thing is to act quickly. Filing or paying as soon as possible can significantly reduce how much the situation costs you overall.
2) If you file late: the late filing penalties (even if you owe £0)
Filing your Self Assessment return late triggers automatic penalties. These apply regardless of how much tax you owe and even if you have already paid your bill in full.
According to official guidance from HMRC, late filing penalties follow a fixed structure:
- £100 immediate fixed penalty as soon as your return is late
- After 3 months: £10 per day for up to 90 days Maximum daily penalties of £900
- After 6 months: an additional penalty of £300 or 5% of the tax due, whichever is higher
- After 12 months: a further £300 or 5% of the tax due, whichever is higher
These penalties are cumulative. The longer the return remains outstanding, the more they stack up.
Key point many people miss: the £100 fixed penalty applies even if you owe no tax at all or you have already paid everything due. Late filing is penalised separately from late payment.
This is confirmed in HMRC’s official guidance on: Self Assessment late filing penalties
3) If you pay late: late payment penalties and interest
Late payment is treated separately from late filing.
This means you can be fully up to date with your tax return and still face penalties if the tax itself is paid late.
If you miss the payment deadline, HMRC applies late payment penalties based on how long the tax remains unpaid.
The standard late payment penalties are:
- 5% of the unpaid tax once you are 30 days late
- 5% of the unpaid tax once you are 6 months late
- 5% of the unpaid tax once you are 12 months late
These penalties are added on top of the original tax bill and any other charges already in place.
In addition to penalties, interest is charged on the outstanding tax from the day after the payment deadline until the balance is cleared in full.
HMRC’s interest rate is linked to the Bank of England base rate and can change over time. To avoid relying on outdated figures, it is important to check the current published rate.
You can find the latest official rates here: HMRC interest rates for late and early payments
If you cannot pay the full amount, paying something is still better than paying nothing. Reducing the outstanding balance lowers the penalties and interest that continue to build.
4) What HMRC typically does next
If you miss a Self Assessment deadline, HMRC will usually begin a standard, step by step process.
This is largely automated, which means things continue to move forward unless you take action.
In most cases, you can expect the following:
- A penalty notice confirming late filing and or late payment penalties. These are normally issued automatically and appear in your online account and by post.
- Your online Self Assessment account to update, showing the tax due, interest, and penalties as they accrue over time.
- Debt collection activity if the balance remains unpaid. This can include reminders, demands for payment, and escalation to HMRC’s debt management team.
At this stage, many people worry that HMRC will move straight to enforcement. In reality, there is usually a window where you still have options, but those options reduce the longer the debt is ignored.
The earlier you engage with HMRC, the more flexibility you tend to have. This can include setting up a payment plan, disputing penalties, or correcting figures if something has been submitted incorrectly.
HMRC explains this process in more detail on: What happens if you miss the Self Assessment deadline
Ignoring the issue rarely improves the outcome. Taking action ensures penalties stop increasing and keeps more solutions on the table.
5) Damage control: what to do immediately, in the right order
If you have missed a Self Assessment deadline, the most important thing is not to freeze. There is a clear order of actions that can limit penalties, reduce interest, and keep your options open.
Step 1: Submit the return as soon as possible, even if you cannot pay
Filing your tax return stops late filing penalties from escalating. The longer the return remains outstanding, the higher the risk of daily penalties and the six and twelve month charges being added.
This applies even if you cannot pay the tax straight away. Filing and paying are treated separately, and submitting the return is always the first priority.
Step 2: Pay what you can immediately
If you cannot clear the full balance, paying something straight away is still worthwhile. Interest and late payment penalties are calculated on the unpaid amount, so reducing the balance reduces the ongoing cost.
Even a partial payment can make a noticeable difference over time, particularly if the debt is likely to remain outstanding for several months.
Step 3: Set up a Time to Pay arrangement if you cannot pay in full
If paying in full is not realistic, you may be able to spread the cost using a Time to Pay arrangement. This allows you to pay your tax bill in instalments based on what you can afford.
HMRC actively promotes Time to Pay around Self Assessment season and is often more flexible when you engage early.
You can start the process here: Pay your HMRC tax bill in instalments
Step 4: Keep evidence of anything that caused the delay
If there is a chance you may appeal penalties, keep clear records of what caused the delay. This could include dates, screenshots, reference numbers, medical evidence, bereavement documentation, or proof of system issues.
Having this information ready makes the appeal process far easier and improves your chances of a successful outcome if you had a genuine reason.
