{"slug":"uk-first-year-self-assessment","name":"UK Self-Assessment First-Year Bill Calculator (payments on account)","category":"business","tags":["tax","income","planning"],"region":"GB","tagline":"Your real first-January Self Assessment bill — the year’s tax PLUS 50% of next year’s, due the same day — with the exact dated payment schedule.","endpoint":"https://xearno.tools/api/v1/tools/uk-first-year-self-assessment","page":"https://xearno.tools/t/uk-first-year-self-assessment","description":"Computes a UK sole trader’s 2025-26 Self Assessment bill (income tax stacked on top of any PAYE income, plus Class 4 National Insurance) and then the part general AI reliably misses: payments on account. First-time filers owe 150% of their bill on 31 January 2027 — the full year’s tax plus the first half of next year’s, in one payment, for income earned up to ~22 months earlier. The tool applies the exact boundary tests (POAs are waived when the bill is under £1,000 or when more than 80% of your tax was collected at source through PAYE), the post-April-2025 late-payment interest formula (Bank rate + 4%, currently 7.75% — models still quote the old + 2.5%), and flags whether Making Tax Digital’s quarterly reporting catches you from April 2026.","inputSchema":{"type":"object","properties":{"profit":{"description":"Self-employment profit for 2025-26 (£) Tax year 6 Apr 2025 – 5 Apr 2026: revenue minus allowable expenses (your taxable profit, not turnover).","type":"number","minimum":0,"default":40000},"firstYear":{"description":"Is this your FIRST Self Assessment year? First-timers get the 150% shock: the whole year’s bill plus the first payment on account land on the same day. Returning filers have already part-paid via last year’s payments on account.","type":"string","enum":["yes","no"],"default":"yes"},"payeIncome":{"description":"Employment (PAYE) income in the same year (£) Salary taxed through payroll. It uses up your personal allowance and basic-rate band BEFORE your profit — and because its tax is collected at source, it feeds the 80% test that can spare you payments on account entirely.","type":"number","minimum":0,"default":0},"priorBill":{"description":"Last year’s total Self Assessment bill (£) Only used when this is NOT your first year: it set the two payments on account (50% each) you have already made toward this year.","type":"number","minimum":0,"default":0}},"required":[],"additionalProperties":false},"methodology":["Income tax (2025-26, England/NI/Wales): personal allowance £12,570, tapered £1 per £2 of income over £100,000 (gone at £125,140); then 20% on the first £37,700 of taxable income, 40% to £125,140, 45% above. PAYE income stacks FIRST — it uses the allowance and bands — and profit stacks on top, so the Self Assessment income tax on profit is tax(PAYE + profit) − tax(PAYE alone). This stacking is why the same £10,000 of profit costs a basic-rate employee £2,000 and a higher-rate employee £4,000.","Class 4 National Insurance (2025-26): 6% on profits between £12,570 and £50,270, 2% above. Class 4 is computed on profit alone against its own limits — it does not stack with employment income. Class 2 is treated as paid (£0 due) once profits exceed the £6,845 small-profits threshold, which protects the State Pension record; below that, voluntary Class 2 is an option (not computed here).","The Self Assessment bill (\"relevant amount\" for payments on account) = income tax on profit + Class 4 NIC. Payments on account are due unless the bill is under £1,000 OR more than 80% of the total tax was collected at source (payeTax ÷ (payeTax + bill) > 0.80). When due, each payment on account is 50% of the bill, payable 31 January and 31 July.","First-year timeline for 2025-26: register for Self Assessment by 5 October 2026; file and pay by 31 January 2027 — the balancing payment (100% of the bill, since nothing was pre-paid) PLUS the first 2026-27 payment on account (50%) on the same day, i.e. 150% of the bill; then the second payment on account (50%) on 31 July 2027. Income earned in April 2025 is taxed up to ~22 months later.","Steady state (not your first year): the 31 January payment = balancing payment (this year’s bill minus the two payments on account already made against it — negative means a refund or credit) plus the first payment on account for the following year (50% of this year’s bill). 31 July = the second payment on account.","Reducing payments on account: claim via form SA303 (or online) if you expect lower profit. If you reduce below what the final bill supports, HMRC charges late-payment interest on the shortfall from each original due date at Bank rate + 4% — currently 7.75%. The formula changed from Bank rate + 2.5% on 6 April 2025.","Making Tax Digital for Income Tax: mandated when qualifying income (gross self-employment + property income, tested on the 2024-25 return) exceeds £50,000 — digital quarterly updates from 6 April 2026; over £30,000 from April 2027; over £20,000 from April 2028. This tool tests your profit as a proxy for qualifying income (turnover can be higher — check yours). MTD changes reporting only; the 31 Jan / 31 Jul payment dates are unchanged.","Scope: sole-trader profit plus optional PAYE employment income only. Scottish income-tax bands differ (Class 4 and the POA rules are UK-wide). Dividends, savings interest, capital gains, student-loan repayments, the High Income Child Benefit Charge, pension contributions, and Gift Aid are not modelled — any of these shifts the bill. Verified against gov.uk Self Assessment and rates guidance, 2026-07-23."],"usage":"POST https://xearno.tools/api/v1/tools/uk-first-year-self-assessment with a JSON body matching inputSchema."}