--- title: "How to File Self Assessment Online: 2026/27 Step-by-Step Guide" description: "**Updated for 2026/27.** File a Self Assessment return online after the tax year ends, once you have complete income, expense and tax-paid records. For the year from 6 April 2026 to 5 April 2027, the usual online filing and balancing-payment…" url: "https://www.accountingfirms.co.uk/knowledge-bank/how-do-i-file-my-self-assessment-tax-return-online/" updated: "2026-08-12" category: Self Employed --- # How to File Self Assessment Online: 2026/27 Step-by-Step Guide **Updated for 2026/27.** File a Self Assessment return online after the tax year ends, once you have complete income, expense and tax-paid records. For the year from 6 April 2026 to 5 April 2027, the usual online filing and balancing-payment deadline is 31 January 2028. ## Step 1: check whether you need a return Use HMRC's current checker. Common reasons include gross self-employment income above £1,000, partnership income, significant property or investment income, foreign income, capital gains, the High Income Child Benefit Charge or a notice to file. If HMRC has issued a notice, file unless it is formally withdrawn. ## Step 2: register in time If you need Self Assessment and are not registered, notify HMRC by 5 October 2027 for 2026/27. Sole traders register the self-employment source; partners need the partnership details; someone already holding a UTR should not apply for a duplicate. Registration can take time, so do not wait until January for a UTR and online access. ## Step 3: choose filing software HMRC's online service covers many standard returns. Commercial software may be needed for certain residence, trust, partnership, capital-gain or other supplementary pages, and will be increasingly relevant for Making Tax Digital. Check that the product supports every source and attachment you need. ## Step 4: gather the records - UTR and National Insurance number - P60s, P45s, payslips and P11D/benefit information - Self-employed income and expense totals - Property accounts and finance-cost details - Bank interest and dividend statements - Pension contributions and Gift Aid - Capital disposal calculations - Foreign income and foreign tax evidence - Student loan and Child Benefit information - Tax already deducted, including CIS ## Step 5: reconcile self-employed figures Record gross sales before platform or merchant fees. Reconcile bank, cash and payment processors; review private-use costs; and choose actual expenses or the trading allowance where eligible. Apply cash basis or accruals consistently and identify capital allowances separately. ## Step 6: complete every income source Do not enter only the business. Include employment, pensions, rent, savings, dividends, partnership allocations, gains and foreign income where reportable. HMRC may hold third-party figures, but you remain responsible for the complete return. ## Step 7: claim reliefs carefully Enter eligible pension contributions, Gift Aid, employment expenses, losses, Marriage Allowance or other reliefs in the correct section. Keep supporting evidence. A claim should follow statutory conditions, not merely a software prompt. ## Step 8: review the calculation Check total income, Personal Allowance, tax bands, National Insurance, student-loan repayments, Child Benefit charge, tax deducted and payments on account. Compare with the prior year and investigate unexpected changes before submission. ## Step 9: submit and save evidence Make the legal declaration only after reviewing the final return. Save the full PDF or copy, computation, submission receipt and HMRC confirmation number. A draft or “100% complete” software message is not proof that HMRC received it. ## Step 10: pay the amount due Filing and paying are separate. Use the official HMRC payment service and correct UTR reference. The 2026/27 balancing payment and first 2027/28 payment on account are normally due 31 January 2028, with the second payment on account on 31 July 2028. ## Payments on account Each payment is generally half the previous year's relevant liability and applies where the amount and tax-at-source conditions are met. A first-year trader can face a balancing bill plus the first advance instalment together. Reduce payments only when a reasonable current-year forecast supports it; interest applies if reduced too far. ## Amending the return A 2026/27 online return can normally be amended until 31 January 2029. After that, overpayment relief or disclosure procedures may apply. Correct an omission promptly and pay extra tax to reduce interest. ## Late filing and payment A return filed after 31 January can trigger an initial £100 penalty even when no tax is due, followed by daily and further penalties. Late payment creates interest and percentage penalties at statutory points. File on time even if you cannot pay, then contact HMRC about Time to Pay. ## Making Tax Digital for Income Tax MTD begins from April 2026 above £50,000 qualifying income, April 2027 above £30,000 and April 2028 above £20,000. People in scope use compatible software for digital records, quarterly updates and final reporting. Quarterly updates are not a substitute for reviewing the final tax position. ## Common online-filing mistakes - Using net platform receipts as turnover - Leaving employment or bank interest out because HMRC “already knows” - Claiming the trading allowance and actual expenses together - Entering pension contributions in the wrong gross/net amount - Forgetting CIS or PAYE tax already deducted - Submitting without saving the receipt - Assuming filing automatically makes payment - Reducing payments on account without a forecast ## Final checklist 1. Confirm every income source and tax year. 2. Reconcile records to third-party statements. 3. Review reliefs and tax deducted. 4. Sense-check the calculation and payments on account. 5. Submit before 31 January 2028. 6. Save the return and receipt. 7. Pay separately and verify allocation. Use HMRC's official [online filing service](https://www.gov.uk/log-in-file-self-assessment-tax-return) and [deadline guidance](https://www.gov.uk/self-assessment-tax-returns/deadlines). Our [Income Tax payment guide](https://www.accountingfirms.co.uk/knowledge-bank/how-to-pay-your-income-tax-bill/) explains payment methods. ## Frequently asked questions ### Can I file before 5 April 2027? No. The 2026/27 tax year must end first, though you can maintain records and estimates during it. ### Does HMRC's figure replace my records? No. Pre-populated or third-party data must be checked and completed. ### Can I file without paying? Yes. File on time to avoid filing penalties, then pay what you can and contact HMRC promptly. *This guide is general information. Complex residence, gains and foreign income may require specialist software or advice.*