Self Assessment

Self assessment has just had its biggest shake-up in a generation. From 6 April 2026, Making Tax Digital for Income Tax is mandatory for sole traders and landlords with qualifying income over £50,000 — digital records and quarterly updates, not just one January deadline. Meanwhile the familiar risks haven't gone anywhere: penalties start at £100 the day a return is late and escalate sharply from there.

Acumon's tax team prepares and files returns for company directors, the self-employed, landlords, higher earners and people with international affairs. We claim every relief and allowable expense you are entitled to, tell you exactly what to pay and when, and deal with HMRC so you don't have to.

Who Needs to File a Self Assessment Return?

You will usually need to file if you are self-employed with gross income over £1,000; you receive rental income; you are a partner in a partnership; you have untaxed income such as dividends or foreign income; you have capital gains above the £3,000 annual exempt amount; you owe the High Income Child Benefit Charge and don't pay it through your tax code; or HMRC has simply sent you a notice to file. If you are not sure, ask us — filing when you don't need to wastes money, and failing to file when you do attracts penalties and interest.

Key Deadlines and Penalties for 2025/26 Returns

For the 2025/26 tax year: register for self assessment by 5 October 2026 if you are new to it; paper returns are due by 31 October 2026; online returns and the balancing payment are due by 31 January 2027 (or file by 30 December 2026 if you want tax under £3,000 collected through your PAYE code). Payments on account fall due on 31 January and 31 July.

Miss the filing deadline and the penalties stack up: £100 immediately, then £10 a day (up to £900) after three months, then the greater of 5% of the tax due or £300 at six months, and again at twelve months. Late payment adds 5% of the unpaid tax at 30 days, six months and twelve months — plus interest throughout. Our clients simply don't pay these: we work to your deadlines with time to spare.

Making Tax Digital for Income Tax

MTD for Income Tax is now live. From 6 April 2026 it is mandatory where your combined self-employment and property income exceeded £50,000 in 2024/25; the threshold drops to £30,000 from April 2027 and £20,000 from April 2028. Affected taxpayers must keep digital records and send HMRC quarterly updates through compatible software, with a final declaration replacing the traditional return.

We get clients MTD-ready end to end: choosing and setting up the software, digitising records, filing the quarterly updates and the year-end declaration — so the new regime becomes our problem, not yours.

What We Do

We gather your information through a simple checklist, prepare the return, and review it for every relief and allowance available — pension contributions, Gift Aid, the marriage allowance, professional subscriptions and more. We calculate your position across all income types, including dividends (taxed at 10.75%, 35.75% or 39.35% in 2026/27 above the £500 allowance) and capital gains (18% or 24% above the £3,000 exemption). Then we file online, give you a clear payment schedule including payments on account, and handle any HMRC correspondence, enquiries or penalty appeals that follow.

Self-Employed and Landlords

For the self-employed we prepare your accounts, maximise allowable business expenses and capital allowances, and deal with Class 4 National Insurance — plus the MTD quarterly cycle now layered on top. For landlords we handle rental accounts, the finance-cost restriction on mortgage interest, and capital gains on disposals — including the 60-day CGT reporting requirement when you sell a UK residential property, a deadline that catches many landlords out. Where property or trading income is modest, we check whether the £1,000 allowances mean you shouldn't be filing at all.

What You Get With Acumon

• Complete preparation and online filing of your self assessment return
• All income covered: employment, self-employment, property, dividends, gains and foreign income
• Every relief and allowable expense claimed to keep your bill down
• Clear payment schedule, including payments on account, diarised for you
• Making Tax Digital software setup and quarterly updates from April 2026
• HMRC letters, enquiries and penalty appeals handled on your behalf

Get a Fixed-Fee Quote

Tell us what you need and we'll come back within one business day with a clear scope and a fixed price — no hourly-rate surprises. Call 020 8567 3451 or use the form and we'll be in touch.