Self Assessment: Answers to the 20 Most Common Questions in 2026 (Part 8)

The final part of the series

This is Part 8 of the UK Self Assessment From Scratch series — the final instalment. Parts 1 through 7 have taken you from "do I need to file?" all the way through registration, record-keeping, deadlines, calculating your tax, completing the return, and handling what happens after you file.

This part is different in structure. Rather than following a sequential process, it answers the 20 questions that come up most often — situations that fall outside the clean step-by-step narrative but affect thousands of filers every year.

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1. "I missed the 31 January deadline"

The first thing to do is file immediately — today, not next week. The penalty structure escalates the longer you wait:

Late payment of tax also attracts:

• 7.5% interest from the day after the due date
• 5% surcharge on unpaid tax after 30 days
• Further 5% surcharges at 6 months and 12 months

Reasonable excuse: HMRC can cancel the £100 penalty if you had a genuine reasonable excuse for missing the deadline. Accepted examples include hospitalisation, serious illness (yours or of someone you care for), bereavement close to the deadline, and HMRC's own online service being unavailable. Work pressure, a forgotten password, or "I didn't know" are not accepted. To appeal the penalty, write to HMRC explaining the circumstances — the appeal must be made within 30 days of the penalty notice.

Call HMRC Self Assessment on 0300 200 3310 if you need to discuss the position before filing.

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2. "I received a Notice to File but don't think I should be in self assessment"

A Notice to File (SA316) is a legal demand. You have two options — but ignoring it is not one of them.

Option A: File the return. Even if you have nothing to declare, you can file a return showing nil additional liability. This closes the matter for that year.

Option B: Apply to be removed from self assessment. If your circumstances genuinely no longer require you to file — you've stopped self-employment, your income is now fully covered by PAYE, and none of the other triggers from Part 1 apply — contact HMRC to explain. You can do this by phone (0300 200 3310) or by writing. If HMRC agrees to remove you, they will confirm this formally and the notice for that year will be withdrawn.

The key point: until HMRC formally withdraws the notice, you must treat it as binding. The late filing penalties run from 31 January regardless of whether you agree you should be in the system.

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3. "I want to de-register and close my self assessment account"

You can leave the self assessment regime if your circumstances have changed permanently. The process:

1. Make sure all outstanding returns are filed and any tax owed is paid.
2. Call HMRC (0300 200 3310) or write to explain why you no longer need to be in self assessment (for example: "I closed my self-employed business in December 2025 and my only income is now PAYE employment below £100,000").
3. HMRC will review and, if they agree, send written confirmation that you are no longer required to file.

Keep records for 5 years after the last return's deadline, regardless of de-registration. HMRC retains the right to open a discovery assessment for earlier years, and you will need your records to respond if they do.

De-registration does not retroactively cancel penalties for any year you were enrolled and failed to file.

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4. "I have crypto or NFT disposals — how does this work?"

HMRC treats cryptoassets (Bitcoin, Ethereum, other tokens, NFTs) as capital assets. Each of the following is a disposal for CGT purposes:

• Selling cryptocurrency for sterling or another fiat currency
• Swapping one cryptocurrency for another (even if no fiat is involved)
• Using cryptocurrency to purchase goods or services
• Gifting cryptocurrency to anyone other than a spouse or civil partner
• Losing access to a wallet (in limited circumstances — HMRC's guidance is strict here)

Share pooling

HMRC's Section 104 pooling rules apply. Every time you buy the same token, the purchase is added to a pool. Your cost basis is the average cost per unit across the whole pool. When you sell, you use the average pool cost to calculate your gain. This prevents taxpayers from cherry-picking low-cost lots to minimise gains.

The same-day rule and 30-day rule (bed and breakfast rules) also apply: if you sell and repurchase the same token on the same day or within 30 days, HMRC matches the disposal to the new purchase, not the pool — preventing deliberate loss-harvesting.

DeFi and staking

Staking rewards, yield farming income, and liquidity mining rewards are treated by HMRC as miscellaneous income (taxed as income tax, not CGT) in the year received, based on their sterling value at the time. This is confirmed in HMRC's CRYPTO22000 guidance.

Staking is not treated as a disposal of the staked assets (for liquid staking, HMRC's position is still evolving — seek specialist advice for large positions).

CARF enforcement from 2026

The Crypto-Asset Reporting Framework (CARF) came into effect for UK exchanges from January 2026. Major platforms are now legally required to report customer transaction data to HMRC. HMRC is matching this data against self assessment returns. If you had crypto gains in 2025/26 and did not declare them, the chance of HMRC identifying this is now significantly higher than in previous years.

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5. "I have a side hustle — does the Trading Allowance apply?"

The £1,000 Trading Allowance applies to gross receipts (before expenses) from self-employment or trading activity:

Once you are above £1,000, you choose your deduction method:

• Trading Allowance: deduct a flat £1,000 from turnover (simpler, but less beneficial if actual expenses are higher)
• Actual expenses: deduct the true costs of the business (better if expenses are significant)

You cannot use both methods for the same business in the same year.

If you sell items regularly online (eBay, Vinted, Etsy, Facebook Marketplace), HMRC distinguishes between selling your own personal possessions (not trading) and buying items with the intention of reselling for profit (trading). The latter is taxable from the first pound if it is your intention to profit — the Trading Allowance then applies to the gross receipts.

From January 2024, platforms are required to report seller data to HMRC if sellers make 30 or more transactions or receive over €2,000 (approximately £1,700) per year. This reporting now feeds into HMRC's data matching.

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6. "I'm employed but also have rental income"

If your rental profit (income minus allowable expenses) exceeds £2,500 in a tax year, you must register for and complete a self assessment return. If it is between £1,000 and £2,500, HMRC may be able to collect the tax through a PAYE code adjustment — contact them to check.

Your self assessment return will include:

• SA102 for your employment income (P60 figures)
• SA105 for your rental income and expenses

Remember the finance costs (mortgage interest) restriction from Part 6 — mortgage interest is entered as a finance cost, not an expense, and attracts a 20% tax credit rather than a full deduction. Higher-rate taxpayers with mortgaged buy-to-lets receive only basic-rate relief on the interest.

If you have rental income from previous years that you did not declare, HMRC operates the Let Property Campaign — a voluntary disclosure facility that typically results in lower penalties than being caught. Details at gov.uk/government/publications/let-property-campaign.

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7. "My income changed a lot this year compared to last year"

Income dropped significantly: use SA303 to reduce your payments on account (see Part 5). File the SA303 as soon as you have a realistic estimate for the current year — do not wait until the July payment is due.

Income increased significantly: your payments on account (based on last year's lower bill) will be insufficient. The difference becomes a balancing payment due on 31 January. Start setting aside additional money now. Use a self-employed tax calculator to estimate the additional liability and make sure your January payment fund is adequate.

First year of self-employment: there are no payments on account in your first year — only the balancing payment for that year, due on 31 January after the tax year ends. But from year two onwards, payments on account begin. Many first-year self-employed people underestimate year-two cash requirements.

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8. "I moved abroad during the tax year"

Moving mid-year may create a split-year position, where you are resident in the UK for part of the year and non-resident for the rest. Under the Statutory Residence Test (SRT), specific cases determine whether split-year treatment applies.

The key implications:

• UK income during the UK-resident part of the year is taxable in the UK in full
• UK-source income (property rental, UK employment) during the non-resident part is still taxable in the UK but only to the extent of UK-source receipts
• You complete SA109 (Residence, remittance basis etc.) to claim split-year treatment
• The SRT is complex — if you moved, especially for employment, HMRC has 8 cases under the SRT that need to be tested in order

Do not assume that leaving the UK means your UK income becomes tax-free. UK rental income, in particular, remains fully within the UK tax regime regardless of your residence.

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9. "Self assessment after someone dies"

When a taxpayer dies, their self assessment obligations do not end immediately. The personal representative (executor or administrator) must:

1. Inform HMRC via Tell Us Once (gov.uk/after-a-death/organisations) — this notifies HMRC and several other government departments simultaneously.
2. Also contact HMRC's dedicated Bereavement line (0300 200 3300) to inform them separately for self assessment.
3. File any outstanding returns for years up to the date of death. The extended filing deadline is the later of 31 January after the year of death, or 3 months after the grant of probate.
4. Report income earned between the start of the final tax year and the date of death.
5. Income earned after death (from the estate — rental income, dividends from shares held in the estate) is reported under the estate's own tax reference, not the deceased's.

The personal representative is not personally liable for the deceased's tax beyond the assets of the estate. If the estate has insufficient funds to pay the tax, HMRC accepts this in most cases — though the tax is a priority creditor in the estate administration, ranking above most other debts.

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10. "Can I do self assessment myself or do I need an accountant?"

Straightforward circumstances — PAYE employment, small self-employment or rental income, no complex assets — are very manageable as a DIY return. HMRC's online system guides you through each step and calculates the tax automatically. HMRC also provides a free webchat service and helpline (0300 200 3310) for specific questions.

Where professional help adds clear value:

• Multiple overlapping income sources (employment + self-employment + property + investments)
• Capital gains on business assets, shares in your own company, or complex property situations
• Overseas income or assets
• Large pension contributions or lifetime allowance considerations
• HMRC inquiry or compliance check
• Significant uncertainty about whether an expense or arrangement is allowable

Typical accountant fees for a self assessment return (sole trader or simple affairs): £300–£600 per year. More complex returns (multiple income streams, CGT, foreign income): £600–£1,500. For many people, the fee is more than recovered through legitimate tax savings and the avoidance of errors.

Free and low-cost resources:

• Tax Aid (taxaid.org.uk): free tax advice for people on low incomes
• Low Incomes Tax Reform Group (litrg.org.uk): guidance and tools
• HMRC webchat: real-time answers to straightforward questions

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11. "I am a non-UK domicile — does that affect my self assessment?"

From April 2025, HMRC replaced the long-standing remittance basis with the Foreign Income and Gains (FIG) regime for individuals who are UK resident but not UK domiciled in their first 4 tax years of UK residence.

Under FIG:

• Foreign income and gains in the first 4 years of UK tax residence are potentially exempt from UK tax
• No remittance basis charge applies (the old £30,000 / £60,000 charge is abolished)
• You must make a FIG election on your self assessment return (SA109)
• UK-source income (employment in the UK, UK rental income, UK dividends) is always taxable in the UK regardless

If you are beyond the 4-year FIG window, you are taxed on the arising basis (all worldwide income and gains taxable in the UK, with double tax relief where applicable). The remittance basis is no longer available for new claims.

The FIG regime is complex and the interaction with double tax treaties, home country tax, and timing of UK residence tests requires specialist advice for anything beyond simple cases.

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12. "I received a P800 after I already filed a self assessment return"

This should not happen for a year you are in self assessment. A P800 is HMRC's reconciliation of PAYE records — it is for employees and pensioners outside the SA system.

If you receive a P800 for a year you have already filed a self assessment return:

1. Do not pay the P800 figure without checking.
2. Log in to HMRC Online Services and verify your SA calculation is showing correctly.
3. Call HMRC (0300 200 3310) and tell them you are in self assessment for that year — the P800 should be cancelled as your SA return is the definitive calculation.

In most cases, this is a timing issue where the P800 was generated before HMRC's systems matched your SA return to your PAYE record. It resolves itself once a HMRC agent reviews your account.

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Useful contacts and resources

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End of series: the complete UK Self Assessment From Scratch guide

This 8-part series has covered the full lifecycle of a self assessment return — from first principles to post-filing inquiries. Here is a summary of what each part covers:

Whether you have worked through all eight parts or dipped into the ones relevant to your situation, the goal throughout has been the same: to give you the specific, accurate, practical information you need to handle self assessment confidently — without needing to wade through HMRC guidance written for professionals.

If your situation changes, new income sources appear, or HMRC contacts you, the relevant part of this series is a reference you can return to. And if complexity grows beyond what DIY comfortably covers, the contacts section above will point you towards qualified help.