Oliver Bennett
Why the deadline deserves your attention now
The online Self Assessment deadline is 31 January, and that date carries more weight than many people realise. It is not only the day your return must be filed — it is also the day any tax owed for the previous tax year must be paid. Miss it and HMRC applies an automatic £100 penalty, even if you owe nothing at all. After three months, daily penalties of £10 can begin to build up, with further charges at six and twelve months. There is also a separate 5 October deadline to register for Self Assessment if you have newly become self-employed, started renting out property, or begun receiving income that is not taxed at source.
If you make payments on account, a second instalment is usually due on 31 July, with a balancing payment the following 31 January. Leaving everything to the final week piles pressure on you and your accountant, and that is precisely when avoidable errors creep in.
Gather your income records first
Before you can think about expenses, you need a complete picture of what came in during the tax year, which runs from 6 April to 5 April. The most common cause of a delayed return is a missing figure that nobody can quite locate. Collect everything in one place early — a folder on your computer is fine, as long as it is backed up.
- Employment: your P60, any P45s, final payslips, P11D benefits and company car details
- Self-employment: invoices, till rolls, bank statements and a simple income summary
- Property: rental income, letting agent statements, service charges and ground rent
- Savings and investments: bank and building society interest, dividends, unit trust distributions, and disposals of shares or cryptoassets
- Pensions and benefits: pension income, taxable state benefits and any early drawdowns
- Other income: foreign earnings, tips, commission and casual work
Download statements rather than relying on memory. If you use accounting software, reconcile the year before you export anything — a tidy set of figures saves hours later and reduces the risk of an enquiry.
Confirm which expenses you can actually claim
Allowable expenses are those incurred wholly and exclusively for the purposes of your trade. Everyday costs such as office stationery, accountancy fees, insurance, software subscriptions and travel to temporary workplaces generally qualify. A few areas trip people up:
- Mileage: using simplified expenses, you can claim 45p per mile for the first 10,000 business miles and 25p thereafter
- Working from home: a flat rate of £6 per week, or a reasonable proportion of heating, broadband and phone costs
- Capital items: equipment, tools and computers may attract capital allowances rather than a straightforward deduction
- Professional fees: subscriptions to approved bodies, indemnity insurance and relevant training
- Entertaining: client entertaining is not allowable, though staff entertaining may be
If your turnover is under £1,000, the trading allowance may let you avoid detailed expense records altogether — but you cannot claim it and your actual expenses in the same year. Your accountant can confirm which route suits you better.
Check your tax position, not just your figures
Entering numbers correctly is only half the job. Once your return is drafted, review the calculation carefully. Are the payments on account correct, or should you reduce them if your profits have fallen? Have you accounted for student loan repayments, the high income child benefit charge, or the tapered personal allowance between £100,000 and £125,140?
Reliefs are easy to overlook. Pension contributions and Gift Aid donations extend your basic rate band, and marriage allowance may be transferable if one partner earns below the personal allowance. Check each figure against your records rather than accepting a default, and query anything that looks unfamiliar before you submit.
Build in a buffer before the deadline
Set yourself a personal deadline of mid-December or, at the very latest, the first week of January. Digital services become busier as January progresses, and a forgotten password or an expired login can cost you an evening you did not plan for.
Keep your records for at least five years after the 31 January deadline, as HMRC can open a compliance check within that window. If you are owed a repayment, submitting early means the money reaches your account sooner rather than sitting in the system during its busiest weeks.
Make your accountant's job easy
A good accountant can do far more with a well-organised set of records than with a shoebox of receipts in late January. Send everything in one batch, flag anything unusual — a one-off purchase, a change in how you work, a new source of income — and ask your questions early, while there is still time to plan.
Agree a date for your records to be with them and stick to it. If cash flow is tight, mention it: there may be scope to plan payments, adjust payments on account, or time a purchase to make the most of capital allowances. The earlier the conversation, the more options are on the table.
