UK COMPANY ACCOUNTS FILING
A Self Assessment tax return is the annual filing UK taxpayers submit to HMRC to declare income that is not taxed at source, including self-employment profits, rental income, dividends, capital gains, foreign income, and high earnings above £100,000. The main return form is the SA100, supported by additional pages for specific income types. The online filing deadline is 31 January following the end of the tax year; the paper deadline is 31 October.
This page covers who needs to file, all four key deadlines, what records you need, the 2026/27 tax bands, late filing penalties, and the new MTD for Income Tax rules that change Self Assessment for sole traders and landlords above £50,000. MicroFiler files Self Assessment tax returns by email for a fixed fee of [£XX].
THE PROCESS
A Self Assessment tax return is the system HMRC uses to collect income tax and National Insurance on income that is not taxed at source through PAYE. The return is filed annually using the SA100 main form, with supplementary pages added for specific income types; SA103 for self-employment, SA105 for UK property, SA106 for foreign income, SA108 for capital gains, and so on.
Self Assessment is also called a tax return or simply self assessment. A Self Assessment return covers one UK tax year. The UK tax year runs from 6 April to 5 April. The 2025/26 tax return has a filing deadline of 31 January 2027.
The return does three things:
THREE FILINGS PER YEAR
all income that has not had tax deducted at source
the total tax and National Insurance owed for the year
the position by triggering a balancing payment or refund
Self Assessment is being replaced by Making Tax Digital for sole traders and landlords above the £50,000 income threshold from April 2026 onward, but it remains the system for everyone else who needs to declare untaxed income.
SERVICE SCOPE
You need to file a Self Assessment tax return if HMRC has asked you to file, or if your circumstances meet any of the categories below. Filing is required even if no tax is owed.
Sole traders with gross self-employment income above £1,000 in the tax year must register for Self Assessment and file a return. The £1,000 trading allowance lets individuals earn up to that amount tax-free without filing, but income above the allowance triggers the obligation.
From 6 April 2026, sole traders with combined self-employment and property income above £50,000 filed under MTD for Income Tax instead of standard Self Assessment. Sole traders below the threshold continue to file Self Assessment until phased mandation extends to lower thresholds in April 2027 (£30,000) and April 2028 (£20,000).
Landlords with gross rental income above £1,000 must declare it on a Self Assessment tax return. The £1,000 property allowance applies the same way as the trading allowance; income up to £1,000 is tax-free without filing; income above triggers the requirement. Joint owners declare their individual share.
The same MTD threshold applies to landlords from April 2026 onward.
Anyone with total taxable income above £100,000 is required to file a Self Assessment regardless of how the income arises. The Personal Allowance tapers between £100,000 and £125,140, and the calculation is done through Self Assessment.
Company directors with income beyond their PAYE salary including dividends, director's loans repaid with interest, benefits in kind not fully taxed through payroll need to file Self Assessment to settle the balance. Directors of dormant companies typically do not need to file unless they have other untaxed income.
You file Self Assessment if you have:
Most employees taxed entirely through PAYE do not need to file a Self Assessment. Tax adjustments can be made through the tax code, P800 calculations, or simple HMRC online claim forms for items like marriage allowance, professional fees, and uniform expenses.
WHO NEEDS TO FILE
The Self Assessment tax return has four key dates each year. Missing any of them triggers automatic penalties or interest charges. Each deadline applies to the tax year that ended on the previous 5 April.
Online Filing
31 January is the main Self Assessment deadline. It is the date by which the online return must be submitted and any tax owed for the previous tax year must be paid. The 2025/26 tax return is due by 31 January 2027, with all tax for that year payable on the same date.
The 31 January deadline also covers the first payment on account for the new tax year, where applicable.
Paper filing deadline
31 October is the deadline for paper SA100 returns. Paper filers must submit three months earlier than online filers to give HMRC time to process the return. Anyone filing after 31 October must file online as paper returns submitted after that date are penalised even if received by 31 January.
Second Payment
31 July is the deadline for the second payment on account. Payments on account are advance payments toward the next year’s tax bill, calculated as half of the previous year’s tax liability. They apply to taxpayers whose tax owed exceeded £1,000 and where less than 80% of tax was collected through PAYE.
Self Assessment
5 October is the deadline to register for Self Assessment if you became liable to file during the tax year that has just ended. New sole traders, new landlords, and new high earners must notify HMRC by 5 October following the end of their first relevant tax year. Late registration may attract a “failure to notify” penalty in addition to any late filing penalty.
KEY DATES
Filing a Self Assessment tax return runs in four steps from registration to submission. The process takes most taxpayers between two and ten hours depending on the complexity of their income sources.
First-time filers register through HMRC’s online service to receive a Unique Taxpayer Reference (UTR). The UTR is a 10-digit number that identifies your tax record and is required for every future filing. HMRC issues the UTR by post within 10 to 21 working days.
Once registered, you also receive a Government Gateway user ID and password, which give you access to the HMRC Self Assessment online portal.
The SA100 main form covers personal details, employment income (if any), pension contributions, charitable giving, and tax adjustments. Supplementary pages are added for each specific income type that are SA103 for self-employment, SA105 for UK property, SA106 for foreign income, SA108 for capital gains, SA109 for residence and remittance.
The HMRC online filing service auto-loads the appropriate supplementary pages once you confirm your income types in the early questions.
Before starting the return, gather records of every income source for the tax year and every allowable expense. The exact records depend on your income mix including payslips and P60 for employment, bank statements and invoices for self-employment, rental statements for property, dividend vouchers for shares, and so on. The records section below details the standard list.
Submit the completed return through the HMRC online portal. Once submitted, HMRC calculates the tax owed and shows the figure for payment. Tax can be paid by bank transfer, debit card, direct debit, and for amounts under £3,000 collected through your PAYE tax code if you file by 30 December.
Filing a Self Assessment tax return requires complete records of every taxable income source and allowable expense for the tax year. The 7 record categories below cover most filers.
Records can be kept on paper or digitally. Digital records are not currently mandatory for Self Assessment, that requirement applies only to taxpayers within MTD. Records must be kept for 5 years and 10 months from the end of the tax year for self-employed and landlord filers, and 22 months for other filers.
The tax owed on a Self Assessment return depends on income type and total taxable income for the year. For 2026/27, three income tax bands apply across England, Wales, and Northern Ireland, with the Personal Allowance frozen at £12,570. Scotland operates a separate set of bands.
Up to £12,570
Tax Rate 0% (Personal Allowance)
£12,571 to £50,270
Tax Rate 20% (basic rate)
£50,271 to £125,140
Tax Rate 40% (higher rate)
Above £125,140
Tax Rate 45% (additional rate)
The Personal Allowance is reduced by £1 for every £2 of income above £100,000, and is fully withdrawn at £125,140. This creates an effective marginal tax rate of 60% on income between £100,000 and £125,140 which is a significant planning point for higher earners and a common reason directors and senior employees fall into Self Assessment.
The Personal Allowance and bands are frozen until April 2031 under current legislation.
Sole traders pay National Insurance through Self Assessment, alongside income tax on their profits.
No longer payable as a separate flat-rate charge. Sole traders with profits above the lower threshold (£12,570) automatically receive National Insurance credits towards the State Pension without paying.
Paid on profits above the threshold, in addition to income tax. For 2026/27, the rate is 6% on profits between £12,570 and £50,270, and 2% on profits above £50,270.
Class 4 NI is calculated alongside income tax on the same Self Assessment return. Many first-time sole traders are caught out because Class 4 NI is added to income tax, not charged instead of it.
The Self Assessment bill is calculated as follows: total taxable income for the year (after the Personal Allowance), less any allowances such as the trading or property allowance, less any reliefs such as pension contributions or Gift Aid, taxed at the relevant rate band. Class 4 NI is added on top for self-employed income. Dividend income is taxed separately at dividend rates (10.75% basic, 35.75% higher, 39.35% additional from April 2026), with a £500 dividend allowance.
The HMRC online portal performs these calculations automatically once income figures are entered. The figure shown after submission is the amount payable by 31 January.
Filing a Self Assessment tax return through MicroFiler costs a fixed fee of [£XX], with all submissions handled by email and filed directly with HMRC on your behalf. There are no additional charges for follow-up questions or filing confirmations.
| Filing route | Typical cost |
|---|---|
| DIY through HMRC online portal | Free (your time only) |
| High street accountant | £200–£500+ per return |
| MicroFiler fixed-fee service | [£XX] per return |
The fixed fee covers the SA100 main form and all supplementary pages relevant to your income mix including self-employment, property, foreign income, dividends, capital gains, and so on. There is no extra charge for adding a supplementary page to the same return.
MicroFiler’s Self Assessment service covers every income type on a single fixed fee, with the full process handled by email. You share your records, we prepare the return, and you approve it before we file with HMRC.
Pricing: [£XX] per Self Assessment return
The fixed fee covers all income types within a single return. Sole trader income, rental property, dividends, capital gains, foreign income, and high-earner adjustments are all included. There is no surcharge for adding supplementary pages to the same SA100.
LATE FILING
Late filing of a Self Assessment tax return triggers automatic financial penalties from HMRC, even where no tax is owed. Penalties escalate the longer the return remains outstanding, and interest is charged separately on any tax that is paid late.
A flat £100 penalty is issued the day after the 31 January deadline, regardless of whether tax is owed. This penalty applies even if your eventual tax bill is zero or you are due a refund.
If the return is more than three months late, HMRC adds £10 per day in daily penalties for up to 90 days, a maximum of £900 on top of the original £100. The daily charges run from 1 May until either filing or the 90-day cap is reached.
After 6 months, a further penalty of £300 or 5% of the tax owed, whichever is higher, is charged. After 12 months, another £300 or 5% is added. A late return that goes the full 12 months can therefore attract over £1,600 in penalties before tax and interest.
Interest accrues on any unpaid tax from the day after the 31 January payment deadline at HMRC’s published rate. Interest charges are separate from late filing penalties and apply even when the return itself was filed on time.
HMRC accepts appeals where the taxpayer has a reasonable excuse, serious illness, bereavement, postal delay, technical issues with the HMRC portal, or other circumstances beyond reasonable control. Appeals must be made within 30 days of the penalty notice. Routine reasons such as being too busy, forgetting the deadline, or unfamiliarity with the system are not accepted as reasonable excuses.
Self Assessment remains the system most UK taxpayers with untaxed income use to settle their annual tax position with HMRC, with the 31 January online deadline as the date that matters most. From April 2026, sole traders and landlords above £50,000 file under MTD for Income Tax instead, and the threshold drops further in 2027 and 2028. MicroFiler files Self Assessment returns for [£XX] per return, by email, with all supplementary pages and income types covered in one fixed fee. For limited company directors, your company’s annual accounts and corporation tax return is filed separately and on a different deadline.
Self Assessment is the annual single-return system that has been in place since 1996. MTD for Income Tax is the new digital system that replaces Self Assessment for sole traders and landlords above the £50,000 income threshold from April 2026, with phased reductions to £30,000 in 2027 and £20,000 in 2028. MTD requires digital records and four quarterly updates per year, plus a year-end final declaration in place of the SA100. Taxpayers below the MTD threshold continue to file Self Assessment as before.
Sole traders and landlords mandated into MTD file a final declaration through MTD software instead of an SA100 Self Assessment return. The final declaration covers the same year-end figures and serves the same legal purpose. Tt is the MTD-format equivalent of Self Assessment for sources within MTD. Other income sources, such as employment income or dividends, are reported on the same final declaration.
Most returns are completed and filed within 5 to 10 working days from when your records are received. Faster turnaround is possible during quieter months but busier periods around the 31 January deadline may extend this slightly. Records received in November or December are generally filed before Christmas.
Yes. HMRC’s online portal allows direct filing at no cost. Most self-employed and landlord filers use an accountant because the supplementary pages, allowable expenses, and tax band calculations require some familiarity with the rules. The DIY option is most appropriate for taxpayers with one simple income source and no complex deductions.
Yes, if your gross rental income exceeds £1,000 in the tax year. Rental income above the £1,000 property allowance must be declared on Self Assessment. Joint owners declare their individual share. For example, a couple jointly receiving £20,000 rental income each declare £10,000.
A Unique Taxpayer Reference (UTR) is the 10-digit number HMRC issues to identify your Self Assessment record. It is required on every return. New filers register through HMRC’s online service and receive their UTR by post within 10 to 21 working days. Lost UTRs can be retrieved from previous return correspondence or by signing in to the HMRC online portal.
You have 12 months from the original 31 January deadline to amend a Self Assessment return online. Amendments outside the 12-month window must be made by writing to HMRC with a corrected calculation, and HMRC may require an “overpayment relief” claim if the correction reduces tax owed.
You do not normally need to file Self Assessment if all your income is taxed through PAYE and you have no untaxed sources. Common exceptions are total income above £100,000, dividend income above £500, savings interest above the Personal Savings Allowance, capital gains above £3,000, or any rental, foreign, or self-employment income.
Filing on time is more important than paying on time as late filing triggers automatic penalties, while late payment triggers interest only. If you cannot pay, HMRC offers Time to Pay arrangements that spread the bill over up to 12 months for amounts under £30,000, and longer for higher amounts. Setting up Time to Pay through your HMRC online account avoids the 5% late payment penalty that applies after 30 days.
Yes. Late returns for previous tax years can be filed through our service. The fixed fee per return applies regardless of which year’s return is being filed. Penalty notices already issued by HMRC must be appealed separately or paid where the appeal is unsuccessful.
Not always. Directors of trading companies typically file Self Assessment if they receive dividends above £500, have other untaxed income, or earn over £100,000. Directors of dormant companies whose only income is a salary fully taxed through PAYE generally do not need to file.
HMRC issues a Self Assessment notice to file (SA316) where its records show you may be liable. Receiving a notice creates a legal obligation to file even if your circumstances have changed. Conversely, not receiving a notice does not exempt you, it remains your responsibility to register by 5 October if you become liable in a new tax year.