NOT financial advice - seek advice from a professional for your specific situation

    TaxKilnUK tax guidance
    TaxKilnUK tax guidance

    Companion Guides

    TaxKiln's companion guides cover the moments standard tax content ignores — the week you go self-employed, the month you hit the VAT threshold, the day HMRC writes to you. Each guide walks through what to do, when, and what it costs in pounds if you get it wrong. Guides are grouped into four categories: life-stage journeys for the big transitions, cost-of-mistake guides showing the pound impact of common errors, decision frameworks for structural choices like Ltd vs sole trader, and 'nobody covers this' guides for situations that fall between the cracks.

    Last reviewed:

    Guidance, not advice. We explain the rules, we don't assess your situation. Always seek financial or tax advice from your accountant, or contact HMRC. Read our editorial scope →

    Life-stage journeys

    Step-by-step guides for the key moments in your self-employed life — from your first week of trading through to selling the business or closing down. Each guide walks you through what to do, when, and what it costs if you get it wrong.

    Cost-of-mistake guides

    How much common tax mistakes actually cost you in pounds, at three profit levels. Not scare tactics — just the numbers, so you can decide what's worth fixing first.

    • 10 Common Tax Mistakes with £ Costs

      The 10 most expensive self-employed tax mistakes, with approximate costs at £30k, £60k and £100k profit.

    • What's My REAL Tax Rate?

      The complete UK self-employed tax stack — income tax, Class 4 NI, student loans, HICBC — with marginal rates at £20k, £60k, £100k and £150k.

    Decision frameworks

    The big structural decisions — Ltd vs sole trader, VAT schemes, employee vs subcontractor — framed as decision tools with real numbers, not textbook chapters.

    • The £90,000 VAT Decision

      When VAT registration is compulsory, when it's smart, and which scheme — Standard, Flat Rate, Cash Accounting — saves you most.

    • Should I Go Ltd?

      Sole trader vs limited company in 2025/26 with real numbers at £30k, £50k, £80k, £120k and £200k profit — and why the old rule of thumb is dead.

    • Should I Register for VAT Voluntarily?

      Decision tree for voluntary VAT below £90k — which trades win, which lose, and the real cost of MTD software and flat rate schemes.

    • Employee or Subcontractor?

      UK employment status tests, IR35, CIS, CEST, and what misclassification costs after backdated PAYE, employer NI and pension arrears.

    Nobody covers this

    The life situations that fall between the cracks of standard tax guides — buying a house as self-employed, getting divorced, your spouse helping in the business, running a side hustle alongside a day job.

    • Self-Employed Tax Calendar

      Every HMRC and Companies House deadline, month by month, with penalties for missing each one.

    • The HMRC Letter — What to Do

      10 common HMRC letters explained: what they mean, the exact deadline, and how to respond — from SA302 to Section 9A enquiry.

    • Side Hustle AND a Job — UK Tax Guide

      How PAYE salary and self-employed income stack, the £1,000 trading allowance, student loans, HICBC, and the cash-flow shock of payments on account.

    • My Spouse Wants to Help in the Business

      Tax-efficient structures by profit level — Marriage Allowance, employing your spouse, 50:50 ordinary shares — and the settlements legislation traps to avoid.

    • Self-Employed and Buying a House

      How lenders read your SA302, the tax-vs-mortgage trade-off, stamp duty in all three UK nations, LISA mechanics, and the home-office CGT trap.

    • Divorce Tax for the Self-Employed

      The FA 2023 CGT reform, business valuation by SJE, pension sharing orders, maintenance treatment, and HICBC after separation.

    Frequently asked questions

    What happens if I miss the Self Assessment deadline?+
    The Self Assessment deadline is 31 January (online filing) for the previous tax year. Miss it and HMRC apply an automatic £100 penalty. Beyond that: £10 per day from 3 months late (capped at £900), 5% of tax due at 6 months late, and another 5% at 12 months late, under Schedule 55 of the Taxes Management Act 1970. If you have a genuine reason (serious illness, bereavement, technical issue with HMRC's systems) you can appeal with evidence; HMRC accepts reasonable excuse appeals in most genuine cases.
    Do I need an accountant or can I file Self Assessment myself?+
    Legally you can file Self Assessment yourself via gov.uk for free, most simple sole-trader returns (single income source, basic expenses) are realistic to self-file. An accountant adds real value when: your trading profit is above £40,000 (extraction-strategy decisions matter), you have multiple income streams (PAYE + self-employment + property + dividends), you've crossed the £90,000 VAT threshold, you're considering incorporation, or you have an HMRC enquiry. Expect to pay £400-£1,500/year for a typical sole-trader accountant; the cost is itself a deductible expense.
    How do payments on account work?+
    When your Self Assessment tax bill exceeds £1,000 for the first time, HMRC requires payments on account toward NEXT year's tax. Half the current bill is due 31 January (alongside the current bill); the other half is due 31 July. So your first January after crossing the threshold can hit with a double-bill: last year's balance + first payment on account. Adjust via Form SA303 if you expect next year's income to drop substantially. Payments on account don't apply if more than 80% of your tax is collected via PAYE.
    What are companion guides and how do they differ from the relief pages?+
    Relief pages explain one statute-defined tax relief — AIA, BADR, the Trading Allowance — top to bottom. Companion guides take the opposite cut: they start from a real-life moment ('I just went self-employed', '10 common mistakes', 'every HMRC deadline this year') and pull in whichever reliefs, calculators and deadlines apply to that moment. Same content library, different entry point.
    Do these guides constitute tax advice?+
    No. TaxKiln is editorial content built from statute, HMRC manuals and published case law. It is not personalised tax advice and not regulated by the FCA. Use the guides to understand the structure of the question, then make the call yourself or take it to a qualified accountant or tax adviser before acting near a threshold or penalty.
    How often are companion guides updated?+
    Each guide carries a lastReviewed date at the top and bottom of the page. Rate-stamped facts are re-checked every UK tax year (after the Spring Budget and again after the Autumn Statement). Statute references are reviewed when the underlying Act changes. If you spot a rate that has moved since lastReviewed, the gov.uk source linked from the relevant relief page is always the live position.
    Why no email capture, login or 'unlock this guide' wall?+
    Editorial integrity. TaxKiln is a read-only publisher: every page is fully available to every reader on the first click, with no signup, no tracking pixels, no behavioural retargeting and no upsell into a paid tier. Sponsorship of the site is governed by a public commitments document; readers are never the product.

    Last reviewed: