Self Assessment and the dates to plan for.
Check whether you need a return, which income to report and how Making Tax Digital changes your record keeping.
Who has to file
Sole traders, landlords, directors with untaxed income, high earners, CGT disposals, foreign income, six distinct triggers, one shared return.
Jump to section 02The four dates
Registration by 5 Oct, paper return 31 Oct, online return + balancing payment 31 Jan, second Payment on Account 31 Jul.
Jump to section 03What MTD changes
Quarterly digital updates now apply above £50k qualifying income, dropping to £30k in 2027 and £20k in 2028.
Jump to section 04Where filers lose money
Under-claimed expenses, forgotten Payments on Account, missed higher-rate relief on pensions and Gift Aid, late-filing penalties from day one.
Jump to sectionWho Has To File a Return
Check the filing criteria for the tax year from 6 April to 5 April. Some reasons always require a return; other untaxed income needs a check with HMRC:
- Sole trader gross income over £1,000, the test is income before expenses or reliefs, rather than taxable profit.
- Rental income: the £1,000 property allowance has conditions. Above it, tell HMRC and check whether the income must go on a return or can be dealt with another way. Do not treat £1,000 rental profit as a universal filing threshold.
- Untaxed dividends or other income: a director may need a return, but the amount and how HMRC collects the tax matter. Being a director alone is not a filing requirement.
- Other filing reasons: partners in a business partnership must file. High Income Child Benefit Charge can require a return where it is not paid through PAYE. A high PAYE-only salary, or being a company director, does not by itself require Self Assessment from 2024/25.
- Capital gains: tax on a chargeable gain can require a return. This is about the gain and available reliefs, not simply selling an asset for more than £3,000. UK residential property can also need a separate report within 60 days.
- Foreign income: overseas income may need reporting, depending on residence, the income and available reliefs. Check the filing requirement before omitting it.
The Self Assessment Calendar
Four dates matter. Missing any of them costs money. The tax year runs 6 April to the following 5 April. Registration with HMRC (if new) must happen by 5 October after the tax year ends. Paper returns are due 31 October. Online returns and the balancing payment are due 31 January. If you pay Payments on Account, a second instalment is due 31 July.
Run the numbers on your own position with our Self Assessment Tax Calculator, it models Income Tax, Class 4 National Insurance, the balancing payment and both Payments on Account in one view.
What 2026 Changes, MTD for ITSA
Sole traders and landlords whose 2024/25 qualifying gross income exceeded £50,000 must now keep digital records and submit quarterly updates to HMRC through compatible software. The annual Self Assessment return remains, but in-scope taxpayers submit it through MTD-compatible software after the quarterly updates and year-end adjustments. The 2025/26 return is tested against £30,000 for April 2027, and the 2026/27 return against £20,000 for April 2028. HMRC is signing up remaining in-scope 2026/27 taxpayers in stages from September 2026; records and software still need to be set up.
The shift is not cosmetic. Spreadsheets on their own no longer satisfy record-keeping rules, digital links are required, and bridging software is mandatory if you continue using Excel. The time to migrate to a compliant bookkeeping setup is before the threshold catches you, not after.
Where Most Filers Lose Money
- Under-claiming expenses, particularly home-office proportioning, vehicle mileage, and pre-trading costs.
- Forgetting Payments on Account, each instalment is normally half the previous year's relevant Income Tax and Class 4 National Insurance after deductions at source. They normally apply from £1,000 outstanding, unless more than 80% was collected at source.
- Late filing penalties, the first £100 hits the day after the deadline regardless of whether tax is owed.
- Reliefs that slip through, pension contributions at higher-rate, Gift Aid, marriage allowance transfers, and SEIS/EIS claims all require active submission.
Go Deeper
MTD for joint landlords
How Making Tax Digital for Income Tax works for jointly owned rental property, including thresholds, Form 17, digital records and quarterly updates.
GuideMaking Tax Digital for Income Tax Guide
Making Tax Digital for Income Tax explained for sole traders and landlords, including current start dates, thresholds, quarterly updates and software.
BriefingPayments on Account Explained
How Self Assessment payments on account work, when they apply, how much is due and when reducing them can create interest.
ComplianceSelf Assessment Deadlines and Penalties
Key Self Assessment deadlines, late filing penalties, late payment interest and what to check before submitting your tax return.
Related Tools & Services
Sort your Self Assessment before the January rush.
We close out the prior year's Self Assessment, file the return ahead of the 31 January deadline, and surface the planning moves that are still available before the new tax year starts.
File your Self Assessment with a Chartered Management AccountantSelf Assessment questions
Who has to file a Self Assessment tax return?
A sole trader normally files when gross trading income exceeds £1,000. Partners in business partnerships also file. Rental income, taxable gains, untaxed income or particular reliefs can create a requirement. Being a director or earning a high PAYE-only salary does not by itself require a return. Check the HMRC criteria for the income and tax year.
When is the Self Assessment deadline?
The usual online deadline for 2025/26 is 31 January 2027, with paper returns due on 31 October 2026. The balancing payment and first payment on account are due on 31 January; the second payment on account is due on 31 July.
Which return determines the MTD start date?
Qualifying gross self-employment and property income in 2024/25 is tested against £50,000 for April 2026. The 2025/26 return uses £30,000 for April 2027; 2026/27 uses £20,000 for April 2028. Test the specified years separately and check exemptions.
What happens if I file late?
The existing late-return rules start with £100 and add daily and further penalties after three, six and twelve months. MTD introduces a different points regime; its quarterly-update easement is specific to 2026/27. The old rules still apply to the 2025/26 return due in January 2027.
Checked 6 September 2026 against HMRC filing criteria, rental income reporting and the dated MTD rules and sources.