Missing the 31 January Self Assessment deadline can feel stressful, but it is a situation many UK taxpayers and business owners find themselves in each year. Whether it was due to missing paperwork, cash flow pressures, or simply underestimating the time involved, the important thing to know is this: all is not lost.

At GW Accountants, we regularly help individuals, landlords and business owners deal with late tax returns, penalties and HMRC correspondence. In this article, we explain what happens if you miss the 31 January deadline, what penalties you may face, and—most importantly—what you should do next to minimise the damage.

What Is the 31 January Deadline?

The 31 January deadline is a key date in the UK tax calendar. It applies to anyone required to submit a Self Assessment tax return.

By 31 January following the end of the tax year, you must:

• File your online Self Assessment tax return
  
• Pay any tax owed for that tax year
  
• Make your first payment on account for the next tax year (if applicable)
  

For example, by 31 January 2026, taxpayers must have submitted their 2024/25 tax return and paid any tax due.

If you miss this deadline, penalties and interest apply automatically, even if you only miss it by one day.

What Happens If You Miss the Deadline?

1. An Automatic £100 Penalty

If your tax return is filed late—even by a single day—HMRC issues an automatic £100 late filing penalty.

This applies:

• Even if you have no tax to pay
  
• Even if you are due a refund
  
• Even if HMRC already knows your tax position
  

The penalty is issued automatically by HMRC’s system, and appeals are only accepted in limited circumstances.

2. Daily Penalties After Three Months

If your tax return is still outstanding three months after 31 January (i.e. after 30 April), HMRC can charge:

• £10 per day, for up to 90 days
  
• Maximum of £900
  

By the end of July, your penalties could already total £1,000, before any tax or interest is considered.

3. Further Penalties at Six and Twelve Months

If the return remains unfiled:

• After six months:
  
  • A further penalty of £300, or
    
  • 5% of the tax due (whichever is higher)
    
• After twelve months:
  
  • Another £300 or 5% of the tax due
    
  • Higher penalties may apply if HMRC believes information is being deliberately withheld
    

At this stage, penalties can become significant, particularly for business owners and landlords.

What About Late Payment of Tax?

Missing the filing deadline often goes hand in hand with missing the payment deadline.

If tax is paid late, HMRC will charge:

Interest on Late Payments

• Interest is charged daily from 1 February
  
• The rate is linked to the Bank of England base rate and can change over time
  
• Interest continues to accrue until the tax is paid in full
  

Late Payment Penalties

HMRC may also apply penalties for late payment:

• 5% of unpaid tax after 30 days
  
• A further 5% after six months
  
• Another 5% after twelve months
  

These are in addition to late filing penalties.

If You Missed the Deadline, What Should You Do First?

1. File the Tax Return as Soon as Possible

The single most important step is to submit the tax return immediately.

• Filing stops daily penalties from building up
  
• It limits further penalties at six and twelve months
  
• It allows you (or your accountant) to see the true tax position
  

Even if you cannot pay the tax yet, filing is still essential.

2. Do Not Ignore HMRC Letters

HMRC will send penalty notices, reminders and sometimes estimated tax demands.

Ignoring these can lead to:

• Higher penalties
  
• Enforcement action
  
• Debt collection or bailiff involvement
  

If you are unsure how to respond, this is where professional advice can make a significant difference.

Can You Appeal a Late Filing Penalty?

You may be able to appeal a penalty if you had a reasonable excuse for missing the deadline.

HMRC may accept appeals for situations such as:

• Serious illness or hospitalisation
  
• Bereavement close to the deadline
  
• System failures beyond your control
  
• Unexpected emergencies
  

HMRC is unlikely to accept excuses such as:

• Being too busy
  
• Forgetting the deadline
  
• Not having the money to pay
  
• Relying on someone else without checking
  

Appeals must usually be made within 30 days of the penalty notice. A well-written appeal, supported by evidence, can improve your chances of success.

What If You Cannot Afford to Pay the Tax?

If you cannot pay your tax bill in full, do not panic and do not ignore it.

Time to Pay Arrangements

HMRC offers Time to Pay (TTP) arrangements, allowing you to spread payments over an agreed period.

You may be eligible if:

• You owe £30,000 or less
  
• Your tax returns are up to date
  
• You can demonstrate affordability
  

In many cases, a payment plan can be set up online. More complex cases may require negotiation with HMRC, where professional support can be valuable.

Interest will still apply, but late payment penalties may be avoided if the plan is agreed early.

What If You Haven’t Filed for Several Years?

Some taxpayers discover they have missed multiple years of Self Assessment returns.

In these cases, HMRC may:

• Issue estimated tax assessments
  
• Demand payment based on assumptions
  
• Apply multiple penalties across years
  

The solution is to:

• Bring all outstanding returns up to date
  
• Correct any incorrect estimates
  
• Negotiate penalties and payment plans
  

At GW Accountants, we regularly help clients with backdated tax returns, often reducing penalties and resolving long-standing HMRC issues.

Can HMRC Investigate You for Late Filing?

Late filing alone does not automatically trigger a full tax investigation. However, repeated non-compliance can increase HMRC scrutiny.

Submitting accurate, complete returns as soon as possible helps:

• Demonstrate cooperation
  
• Reduce the likelihood of further action
  
• Bring matters to a close more quickly
  

How GW Accountants Can Help

If you have missed the 31 January deadline, getting professional advice early can save time, money and stress.

At GW Accountants, we can help by:

• Preparing and submitting late Self Assessment tax returns
  
• Dealing directly with HMRC on your behalf
  
• Advising on penalty appeals
  
• Setting up Time to Pay arrangements
  
• Handling multiple years of outstanding returns
  
• Helping you stay compliant going forward
  

We work with:

• Sole traders and freelancers
  
• Company directors
  
• Landlords
  
• High-earning individuals
  

Our approach is practical, confidential and focused on solutions, not judgement.

How to Avoid Missing the Deadline in Future

Once things are back on track, it is worth putting systems in place to avoid a repeat situation.

Practical steps include:

• Keeping records up to date throughout the year
  
• Setting aside money regularly for tax
  
• Using cloud accounting software
  
• Working with an accountant well before January
  
• Reviewing tax positions earlier in the tax year
  

Early planning almost always results in lower stress and better tax outcomes.

Final Thoughts

Missing the 31 January tax deadline is never ideal, but it is also far more common—and far more fixable—than many people realise.

The key is to act quickly, file as soon as possible, and deal with HMRC proactively. With the right support, penalties can often be reduced, payment pressures managed, and compliance restored.

If you have missed the deadline or are worried about your tax position, GW Accountants are here to help. Getting advice now could make a significant difference to both the cost and the outcome.