Self Assessment Tax – FAQs Q1. Who needs to file a Self Assessment tax return? You must file Self Assessment if you are self-employed earning over £1,000, a partner in a partnership, a company director with untaxed income, a higher earner above £150,000, a landlord with rental income, you have significant savings, dividend, or capital gains income, or you receive foreign income. Many other situations also trigger the requirement. If you are unsure, Atlas Tax Advisors offers a quick free check to confirm whether you need to register and file. Q2. What are the Self Assessment deadlines for 2025/26 returns? For the 2024/25 tax year, the paper return deadline is 31 October 2025 and the online deadline is 31 January 2026. Any tax owed is also due by 31 January 2026, with payments on account due 31 January and 31 July if applicable. Registration deadlines apply for new filers (5 October following the end of the tax year). Atlas Tax Advisors begins preparing client returns from April onwards to spread the workload and avoid the January rush. Q3. What are the penalties for filing Self Assessment late? Missing the 31 January online deadline triggers an immediate £100 fixed penalty even if no tax is due. Further penalties apply at three months (£10 daily, up to £900), six months (5% of tax due or £300, whichever is greater), and 12 months. Late payment also attracts interest and 5% surcharges at 30 days, six months, and 12 months. The penalty regime is harsh, which is why our clients never miss a deadline. Q4. What expenses can I claim as a sole trader? You can claim any expense incurred wholly and exclusively for business, including office costs, professional fees, business insurance, marketing, software, mileage at HMRC-approved rates, a proportion of home costs if you work from home, training to maintain (not acquire) skills, business travel and accommodation, and bank or finance charges. Capital items qualify for capital allowances rather than direct deduction. Atlas Tax Advisors reviews every category to ensure no legitimate expense is missed on your return. Q5. How do I register for Self Assessment for the first time? You need to register with HMRC by 5 October following the end of the tax year in which you started self-employment or received untaxed income. Registration is done online and HMRC issues your Unique Taxpayer Reference (UTR) and activation code by post. Late registration can trigger penalties even if no tax was due. Atlas Tax Advisors handles registration as part of our onboarding for new self-employed clients across Milton Keynes and the wider UK. Q6. What is the £1,000 trading allowance and should I use it? The £1,000 trading allowance lets you earn up to £1,000 a year from self-employment or casual income without registering for Self Assessment or paying tax. Above £1,000, you can choose between deducting actual business expenses or claiming the £1,000 allowance, whichever is more beneficial. The same applies to property income with a separate £1,000 property allowance. We help clients evaluate which method gives the lower tax bill, particularly for side hustles and small online businesses. Q7. How are dividends taxed under Self Assessment? In 2025/26, the dividend allowance is £500, after which dividends are taxed at 8.75% (basic rate), 33.75% (higher rate), and 39.35% (additional rate). Dividend income sits on top of your other income for rate-banding purposes. Limited company directors should plan their salary-and-dividend mix carefully each year. Atlas Tax Advisors models the optimum split for owner-managers based on full personal circumstances, including pensions, savings, and other income, to minimise total tax legally. Q8. Do I need to pay payments on account, and how do they work? If your Self Assessment tax bill is over £1,000 and less than 80% of your income tax was deducted at source, you make payments on account towards next year's liability. The first instalment is due 31 January (alongside the previous year's balancing payment) and the second on 31 July, each equal to half of your prior year's liability. We always explain the cash-flow impact clearly so clients know exactly what to expect long before the date. Q9. Can I amend my Self Assessment return after filing? Yes, you have 12 months from the original 31 January deadline to amend your return online. After that, you can write to HMRC under the overpayment relief rules within four years of the end of the tax year. Honest mistakes are handled sympathetically, but careless or deliberate errors attract penalties. Atlas Tax Advisors' multi-stage review process catches errors before submission, but we are equally happy to amend returns prepared elsewhere if needed. Q10. How can Atlas Tax Advisors help me save tax through Self Assessment? We review every line of your return for opportunities including overlooked expenses, marriage allowance transfer, pension contributions, Gift Aid, professional subscriptions, working-from-home reliefs, student loan thresholds, capital allowances, loss reliefs, and effective tax-rate planning across all income sources. We also help higher earners manage the personal allowance taper between £100,000 and £125,140, where the effective marginal rate hits 60%. Most new clients are surprised by how much we save them in their first year.