Self Assessment Tax Compliance for Businesses UK

Reviewed: 17 June 2026

Self Assessment is HM Revenue & Customs’ system for collecting Income Tax where tax is not fully deducted at source. It commonly applies to sole traders, business partners, landlords and people with other untaxed income. The taxpayer remains responsible for registering when required, keeping records, filing an accurate return and paying tax by the deadline.

Who normally needs to file

Sole traders with gross trading income above the applicable reporting allowance.
Partners in a business partnership.
People receiving rental income or other untaxed income.
Company directors or employees with tax matters that cannot be settled fully through PAYE.
Anyone HMRC has told to submit a return.

Use HMRC’s Self Assessment checker if you are unsure whether a return is required.

Key Self Assessment deadlines

5 October: usual deadline to notify HMRC that you need to complete a return for the previous tax year.
31 October: deadline for most paper returns.
31 January: deadline for most online returns and for paying the balancing amount due.
31 January and 31 July: common payment-on-account dates where payments on account apply.

Confirm the dates that apply to your circumstances using the official Self Assessment deadlines.

Making Tax Digital for Income Tax from April 2026

Making Tax Digital for Income Tax began its first mandatory phase on 6 April 2026. Self-employed people and landlords with qualifying income over £50,000 are brought into the system first, based on the relevant earlier Self Assessment return. The planned threshold reduces to £30,000 from April 2027 and £20,000 from April 2028.

People within scope generally need to keep digital records, use compatible software and send quarterly updates in addition to completing the year-end process. Eligibility depends on the official qualifying-income rules rather than profit alone.

Check whether Making Tax Digital for Income Tax applies and read HMRC’s MTD Income Tax guidance.

Records to keep

Records should support every figure entered on the return. Depending on the activity, this can include sales invoices, expense receipts, bank statements, mileage records, payroll information, asset purchases, loan interest, rental records and evidence for reliefs claimed.

Retention periods vary by taxpayer and circumstance. Sole traders should check HMRC’s self-employed record-keeping rules.

Common compliance mistakes

Registering late because no tax is expected to be due.
Confusing turnover, profit and qualifying income.
Claiming expenses without adequate evidence.
Missing payments on account when budgeting for January and July.
Using software that does not meet the MTD requirements where MTD applies.
Waiting until January to reconcile a full year of records.

Practical annual workflow

Record income and expenses consistently throughout the year.
Reconcile bank accounts and investigate unexplained transactions.
Check whether VAT, PAYE or MTD obligations apply separately.
Review reliefs and unusual transactions before preparing the return.
Submit early enough to correct errors and plan the tax payment.
Keep the final return, calculation and supporting records together.

Related guidance

For wider obligations, visit the UK Tax Compliance hub. Sole traders may also find Sole Trader Accountants UK and Bookkeeping Services in the UK useful.

This page provides general educational information, not personalised tax advice.

Manage Self Assessment as an annual cycle

Self Assessment is not only a January filing task. The return depends on records collected throughout the tax year, registration status, income sources, allowable expenses, tax already deducted and payments on account. From April 2026, some sole traders and landlords also need to use Making Tax Digital for Income Tax, adding digital records and quarterly updates to the annual process.

Confirm who and what the return covers

A business owner may need a return because of self-employment, partnership income, property income, capital gains or other untaxed income. The legal entity matters: a limited company files a Company Tax Return, while directors and shareholders may separately need Self Assessment for their personal income and gains. Do not treat the company return as the owner’s personal return.

List every relevant income source before preparing the return. A bookkeeping system for one trade may not contain employment income, benefits, pensions, savings, dividends, property income, gains or overseas amounts.

Current 2026–27 filing timetable

Tell HMRC by 5 October 2026 if a return is required for 2025–26 and the person is not already within the process.
Paper returns for 2025–26 are generally due by 31 October 2026.
Online returns and the balancing payment are generally due by 31 January 2027.
A second payment on account, where required, is due by 31 July.

HMRC can issue a different deadline in some circumstances. Check the person’s account and notices rather than relying only on a generic calendar.

Records for a business return

Sales, fees and other business income.
Purchase invoices, receipts and expense evidence.
Bank, card and payment-platform statements.
Mileage, travel and home-working records where relevant.
Asset purchases and disposals.
Stock or work-in-progress information where applicable.
Amounts introduced, drawings and private-use adjustments.
Tax deducted at source, pension contributions and Gift Aid evidence.
Property, investment, employment and overseas-income records where relevant.

Separate accounting profit from taxable profit

The return should not simply copy the net profit from bookkeeping. Review private use, capital expenditure, allowable expenses, simplified expenses, losses and other tax adjustments. The treatment can depend on the accounting basis, legal structure and facts. Keep a reconciliation from the business records to the figure entered on the return.

Payments on account

Payments on account are advance payments towards the next Self Assessment bill. They are normally made in two instalments, on 31 January and 31 July, and each is usually half of the previous year’s relevant tax. They are generally not required when the previous amount was below £1,000 or more than 80% of the tax was collected outside Self Assessment.

A January payment can therefore include both a balancing amount for the completed year and the first payment on account for the next year. Build this into the cash forecast. A first-time filer can be surprised because the first January amount may be materially higher than the tax for one year alone.

Illustrative cash-flow example

If the relevant Self Assessment liability for a year is £4,000 and payments on account apply, the first payment on account for the next year would usually be £2,000. The January amount may include the £4,000 bill plus that £2,000 advance payment, with a second £2,000 due in July. The actual calculation can differ because of tax deducted at source, gains, student loans or other items.

Reducing payments on account

HMRC allows a person to apply to reduce payments on account if the next bill is expected to be lower. The estimate should be reasonable and documented. If payments are reduced too far and the final liability is higher, interest can apply. Update the estimate when business results change rather than treating the reduction as permanent.

Making Tax Digital for Income Tax

Making Tax Digital for Income Tax becomes mandatory in phases for qualifying sole traders and landlords. People with qualifying income over £50,000 for 2024–25 need to use it from 6 April 2026; the threshold moves to over £30,000 from 6 April 2027 and over £20,000 from 6 April 2028. Eligibility depends on qualifying self-employment and property income, not total taxable income or profit.

Those in scope need compatible software, digital records and quarterly updates, followed by the annual tax-return process. Quarterly updates do not remove the need to review adjustments and other income before the final return.

Prepare for MTD without duplicating systems

Confirm whether qualifying income puts the person in scope and from which date.
Choose compatible software or a controlled spreadsheet-and-bridging process.
Decide who records transactions and who submits updates.
Separate each self-employment or property business as required by the software and rules.
Reconcile digital records regularly rather than only before an update.
Maintain a list of year-end adjustments and income not included in quarterly updates.

Corrections, late returns and missing information

If information is incomplete, do not silently omit the item or guess without documenting the basis. HMRC provides routes for estimates and later corrections in appropriate circumstances, but the method and disclosure depend on the facts. Keep a list of provisional figures, the evidence still required and who is responsible for obtaining it.

Late filing and late payment can create separate penalties and interest. Submit and pay as soon as possible when a deadline has been missed, while preserving the chronology and any evidence that may be relevant to a reasonable-excuse review. Professional advice is sensible where several years, significant amounts or deliberate errors may be involved.

Working with an accountant or tax agent

Agree a handover date well before January and provide a complete list of income sources, not only a bookkeeping export. Tell the adviser about new property, asset disposals, employment changes, pension contributions, overseas activity and major personal or business events. Review the final calculation, payment schedule and payments-on-account position before approval.

Annual preparation workflow

Confirm the person’s registration and all sources of income.
Close and reconcile business records to the tax-year end.
Collect documents from outside the bookkeeping system.
Prepare business-profit and tax-adjustment schedules.
Review payments on account and estimate the January cash requirement.
Complete a reasonableness review against prior years and current activity.
Approve and submit the return.
Save the return, calculation, submission receipt and payment evidence.

Common mistakes

Missing an income source because it is outside the business bank account.
Confusing turnover with profit for MTD eligibility.
Assuming a quarterly update is the final tax calculation.
Claiming costs without separating private use.
Forgetting payments on account when budgeting for January.
Reducing payments on account without updating the estimate.
Waiting until January to register, gather records or choose software.

Official guidance

Related ASH guides

Important: Personal tax depends on all income, gains, reliefs and circumstances. This guide is not a substitute for a complete tax review.