Every January, thousands of taxpayers scramble to file their Self Assessment return at the last minute. The HMRC portal opens on 6 April (first day of the new tax year) and you can file almost immediately.
Filing early is becoming more common. HMRC recorded a record number of early filers in the 2025/26 tax year, with returns submitted in April reaching over 700k
Spread the cost
Once you know your tax bill, you can plan for it. HMRC’s Budget Payment Plan lets you make voluntary advance payments throughout the year in amounts that suit you.
If you wait until January you’re facing the full amount at once often when post Christmas cashflow is already under pressure.
Payments on Account
Where your Self Assessment tax bill exceeds £1,000, HMRC requires Payments on Account, which are advance payments towards the following year’s liability. These fall due on 31 January and 31 July respectively.
Filing early ensures you understand these obligations well in advance, removing the element of financial surprise. Where income has reduced compared to the prior year, there may also be grounds to apply for a reduction in Payments on Account, an opportunity that requires timely review by your adviser.
Get your refund faster
Overpaid tax during the year? If you’ve overpaid tax through an incorrect PAYE tax code, a change in circumstances, or other reasons then submitting your return early enables HMRC to process the repayment promptly, before the January peak places additional demands on their systems. For business owners, getting overpaid tax back quickly can make a real difference to working capital.
Avoid an escalating penalty regime
The penalties for late filing are automatic and compound over time. Understanding the structure reinforces why early action is always preferable:
- A £100 fixed penalty applies from the first day of late filing
- Daily penalties of £10 per day accrue after three months, up to a maximum of £900
- A further penalty of 5% of the tax due is applied at six months and again at twelve months
- Late payment interest is currently charged at 7.75% on any outstanding balance
Give your accountant time
There’s a meaningful difference between a return prepared under pressure in January and one that’s been reviewed properly over months.
When you share your information early, your adviser can:
- Review your income and expenditure thoroughly
- Identify allowable expenses and reliefs you may have missed
- Advise on tax planning opportunities while there’s still time to act
- Spot anything that could attract an HMRC enquiry and address it proactively
Key dates to bookmark
| 6 April | Tax year begins and HMRC portal opens for new returns |
| 5 October | Deadline to register for Self Assessment for the first time if you have new untaxed income |
| 31 October | Deadline for paper tax return submissions |
| 30 December | Deadline to elect for outstanding tax to be collected via PAYE tax code (if eligible) |
| 31 January | Online return deadline; tax and Class 4 NI payment due; first Payment on Account due |
How Mitchell Charlesworth can help
Our tax team are experts in the field of personal and corporate tax. Their sole aim is to ensure our clients don’t pay a penny more in tax than they need to.
Whether you’re filing for the first time or simply want to move away from the January rush, we’d be happy to help. Get in touch with us to speak to our tax advisers.
