Startup Essentials: Managing the self-assessment deadline process

The January 31 self-assessment deadline is one of those dates that is high on every founder’s agenda, yet often remains a source of last-minute pressure. In our latest Start-up supplies article, which we hear about Graham Davies, CEO of AIN partner Addition Financeabout the crucial steps you need to take now to avoid automatic fines and ensure your financial house is in order in the coming year.

With the January 31 self-assessment deadline just days away, it’s normal to feel under pressure, especially if you run a business or combine multiple income streams. If you’re not quite ready to submit, you’re not alone – but now is the time to take action. Your actions over the next few days can make the difference between a smooth filing and unnecessary stress.

In this article I explain what the deadline means, what happens if you don’t meet it, and how you can manage your self-evaluation quickly and confidently.

What is the deadline for self-evaluation?

The deadline for the self-assessment is January 31 after the end of the tax year. At 11.59pm on 31 January, HM Revenue and Customs expects:

• Your tax return must be filed
• Any tax you owe must be paid

Even filing a few minutes late can result in penalties, so it’s critical that you understand your options before the deadline.

Who must file a tax return themselves?

You usually have to file a tax return if you:

• Are you self-employed or a sole proprietorship?
• Are you a company director (unless all income is taxed via PAYE)
• Earn income outside of PAYE (consultancy, freelance work, extra income)
• Receive rental income from real estate
• Earn significant savings or investment income
• Are affected by the High Income Child Benefit
• Have capital gains to report

Many people assume that taxes are ‘taken care of’ elsewhere – until they realize too late that self-assessment still applies to them.

What documents do you need to submit your tax return?

As you do this together this week, focus on the essentials:

• Details of all income (salary, dividends, freelance, rent, investments)
• Recording of allowable business expenses
• Bank statements showing the savings interest
• Dividend declarations
• Pension contribution details
• Gift Aid donation details
• Your unique taxpayer reference (UTR)

You don’t need flawless files, but you do need complete and honest information.

What happens if you do not submit your application by January 31?

If your return is not submitted on time, HMRC will automatically apply penalties. These are not discretionary and escalate.

This is what usually happens:

• A £100 late filing penalty will be applied immediately after the deadline
• Interest is charged daily on unpaid taxes
• After 3 months, additional daily penalties may apply
• If the delay continues, further penalties will follow

The key point: Penalties are based on tardiness, not intent. Being busy, stressed or insecure doesn’t stop them from building themselves up.

If you’re close, should you still submit?

Yes, but only if it is correct.

Try to file a return that is correct to the best of your knowledge. If a figure is truly missing (for example, you’re waiting for paperwork), you may be able to use an estimated or preliminary figure and then amend the return once you have the final figures.

If you take action now, you can:

• Avoid late filing penalties
• Reduce stress and uncertainty
• Correct or change data later if necessary
• Get clarity on what you owe and schedule payment

For many people, the biggest barrier is simply getting started.

If the January 31 deadline passes and your self-assessment has not yet been submitted, the most important thing is not to freeze. Missing the deadline will result in an automatic late filing penalty from HMRC, but the situation can still be remedied – and acting quickly can prevent it from getting worse.

If you miss the deadline, you must:

• File your tax return as soon as possible
  This will prevent late filing penalties from escalating further.
• Pay what you can, even if it is not the full amount
  Interest will be charged on unpaid taxes, but paying early will reduce the amount that accrues.
• Only use provisional figures if absolutely necessary
  If you wait for final information, you may be able to submit estimated figures and amend the return later. Don’t guess.
• Set up a payment plan if necessary
  If you are unable to pay the full invoice immediately, HMRC may allow a Time to Pay arrangement.
• Get help if you’re not sure
  Acting quickly with support can help limit fines, reduce errors and bring the situation back under control.

The worst option is to do nothing. Even a late filing is much better than continued delay.

Should you do it yourself or call in help?

At this stage, most founders aren’t struggling with the fact that self-assessment is impossible – they’re struggling because they’re trying to fit it into an already overloaded schedule.

If you are still preparing your tax return in the last days before the deadline, the risk is not effort; they are mistakes, missed income or avoidable fines due to haste.

Getting expert support makes sense when:

• Time is tight
• Your income comes from more than one source
• You want certainty that it is done correctly
• Under pressure you don’t want to risk mistakes
• You prefer to outsource it and concentrate on your business

For many founders, outsourcing is not about convenience. It’s about reducing risk and buying peace of mind when it matters most.

Submit your self-assessment without stress

For founders who have yet to submit and don’t want to risk mistakes or fines, Addition Finances helps individuals prepare and submit their self-assessment accurately, even close to the deadline.

Their process is focused on speed and clarity: confirming what is needed, handling the submission, and ensuring nothing is missed if time is tight. To kick-start your self-evaluation with addition leave your details HERE.

The most important takeaway

If the self-assessment deadline is approaching and you feel underprepared, you still have options. If you take action now – even in the final days – you can avoid fines, reduce stress and move forward with confidence. Once filed, there will be immediate relief and you can set up better systems for the coming year.

The most important thing is not to panic, just take the next step.

Graham Davies is the founder and CEO of Addition Finances. Addition combines smart technology with real human support to give ambitious SMEs clarity, speed and confidence in their figures.