UK Self-Assessment: 2026/27

UK Self-Assessment 2026/27: Deadlines, Penalties, MTD ITSA

Q: Who must file a Self-Assessment tax return for 2026/27?

Mandatory SA filers : (a) self-employed earning >£1,000 gross (above trading allowance); (b) partner in business partnership; (c) earning >£50,000 with Child Benefit (HICBC trigger); (d) earning >£100,000 from any source (PA taper); (e) gross dividend income >£10,000 (was £2,000 before April 2024); (f) gross savings interest >£10,000; (g) rental income >£2,500 net (after PIM allowable expenses) or >£10,000 gross; (h) foreign income; (i) capital gains above the £3,000 Annual Exempt Amount; (j) HMRC-issued SA notice ("notice to file"); (k) directors of UK Ltd companies (HMRC guidance - though not strict statutory rule); (l) selling shares / property requiring CGT reporting. Voluntary SA : anyone can request to file SA via gov.uk/register-for-self-assessment - useful for claiming reliefs (Gift Aid higher-rate, pension higher-rate, EIS / SEIS / VCT) without waiting for HMRC P800. Penalty for not filing when required : see late filing penalties table above. Plus Schedule 41 FA 2008 failure-to-notify penalty if you also missed the 5 October registration deadline.

Q: What is Making Tax Digital for Income Tax Self-Assessment (MTD ITSA)?

MTD ITSA replaces annual SA filing with QUARTERLY DIGITAL UPDATES + final-end-of-period declaration. Phase-in by income threshold. April 2026 : self-employed + landlords with gross income >£50,000. April 2027 : threshold drops to £30,000. April 2028 : threshold drops to £20,000 (announced Autumn Budget 2024). Requirements : digital records of all business income + expenses (no manual spreadsheets after April 2026 for affected). MTD-compatible software (Xero, QuickBooks, FreeAgent, Sage etc) submits quarterly updates by month-end of each quarter. End-of-period statement at tax year-end. Final declaration submitted by 31 January following tax year end. Exemptions : digital exclusion (those who genuinely can't use computers - HMRC discretion). Penalties (new MTD-specific regime from April 2026) : points-based - each missed quarterly submission = 1 point. 4 points (£200) = first £200 fine. Then £200 per further missed submission. Points expire after 24 months of compliance. Late tax payment penalties : gradually replacing Schedule 56 FA 2009 surcharges with new MTD-aligned regime.

Q: How do I appeal a Self-Assessment penalty?

Two appeal routes . (1) HMRC internal review : written request within 30 days of penalty notice. HMRC officer (different from original) reviews. Free + simple. Statutory basis Section 49 TMA 1970. Common grounds : (a) "reasonable excuse" - bereavement, serious illness, hospitalisation, postal disruption, HMRC system failure, unexpected events outside control; (b) computational error; (c) HMRC errors; (d) special circumstances under Schedule 55 Para 16 FA 2009 (mitigation). NOT reasonable excuse : forgetting deadline, accountant error, lack of money, ignorance of law. (2) First-tier Tribunal (Tax Chamber) : if internal review unsuccessful OR you skip review. File appeal within 30 days. Form TS1 from gov.uk. Free + represent yourself OR via tax adviser. Appeal grounds : same as above - reasonable excuse + technical legal disputes. Tribunal can reduce penalties more generously than HMRC internal review. Recent precedent : Perrin v HMRC [2018] UKUT 156 established broad "reasonable excuse" interpretation. Bourne v HMRC [2019] UKUT 92 - "ignorance of law" specifically not a reasonable excuse. Higher tribunals : Upper Tribunal + Court of Appeal for points of law. Rare for SA penalty cases - typically First-tier final.

Q: When should I file paper SA100 vs online?

Strongly prefer online filing via Government Gateway. Online deadline 31 January 2028 (3 months later than paper). Paper SA100 : deadline 31 October 2027. £100 fixed penalty for late paper even if you switch to online later. Some scenarios require paper : trustees of certain non-resident trusts, partnership returns (SA800) for years where partnership has complex foreign elements, certain non-standard claims. Most individuals : online preferred. Free HMRC online service handles most situations. Software alternatives (TaxCalc, FTAX, BTC) for complex returns. Online benefits : HMRC pre-fills employment income from RTI feeds, instant calculation, immediate filing confirmation, easier to amend, refunds processed faster (typically 2-3 weeks vs 6-8 for paper). Don't have Government Gateway? Register at gov.uk/log-in-register-hmrc-online-services. Verification via passport/driving licence/credit history + ~3-7 days for HMRC to send activation code by post. Start the process at least 4 weeks before deadline. HMRC support : 0300 200 3310 SA helpline.

Q: What records must I keep for SA + how long?

Self-employed + partnership : 5 years from 31 January submission deadline (so records for 2026/27 → keep until 31 January 2033). All other SA filers : 22 months from end of tax year (so 2026/27 → keep until 31 January 2029). Statutory basis Section 12B TMA 1970. Records to keep : (a) all business income receipts/invoices with date + payer + amount; (b) all business expenses receipts/invoices; (c) bank statements (separate business account preferred); (d) payslips, P60, P11D, P45 from employments; (e) interest certificates from banks/building societies; (f) dividend vouchers; (g) gift aid declarations; (h) capital gains computations + supporting docs; (i) rental property records (income, expenses, mortgage interest, capital improvements). Digital records OK : HMRC accepts electronic copies. MTD ITSA from April 2026 : requires DIGITAL records for affected (>£50k income initially). Manual spreadsheets become non-compliant. Penalties for missing records : £3,000 fine under Section 12B(5) TMA 1970 + likely "best of judgment" assessment by HMRC if records can't substantiate return.

Q: Can I file SA late - what are my options?

If you missed 31 January : file ASAP. £100 fixed penalty already triggered but daily penalties (£10/day) start at 3 months overdue. Filing within first 90 days minimises further penalty accrual. If 3+ months overdue : pay the £100 + accrued daily penalties + file return immediately. Each day of delay costs £10. If 6+ months overdue : penalty £100 + £900 daily (max) + greater of £300 or 5% of tax = potential £1,300+ even before tax-geared penalties. If 12+ months overdue : same as 6 months + additional greater of £300 or 5% (or up to 100% if deliberate). Plus Schedule 24 penalties on tax + Schedule 56 late payment surcharges + interest. Reasonable excuse appeal : see appeal FAQ. Voluntary disclosure : if you've been non-compliant for multiple years, use Digital Disclosure Service (gov.uk/government/news/disclosure-of-tax-and-duty) for structured disclosure with better penalty terms. Don't file blank return to avoid penalty : filing inaccurate return triggers Schedule 24 inaccuracy penalties on top - worse than late filing. Most cost-effective : file accurate return as soon as practicable + appeal penalties with reasonable excuse if available.

Q: How does PAYE interact with Self-Assessment?

PAYE employees have tax + NI deducted at source via tax code (e.g., 1257L). For most, PAYE accounts for full year's tax liability and SA isn't required. SA still needed when : total income from other sources (interest, dividends, rental, self-employed side income) above threshold triggers SA filing; or HICBC applies; or PA taper applies (£100k+ income); or you want to claim higher-rate relief on pension / Gift Aid / EIS / SEIS / VCT. PAYE + SA combined : SA reconciles the WHOLE year's tax position. Any PAYE under-deducted = balancing payment to HMRC. Any over-deducted = refund. Tax code adjustment : if SA shows small under-payment <£3,000, HMRC can adjust NEXT year's PAYE tax code to collect via reduced PA. Avoids one-off cheque. Triggered by 30 December online filing deadline. P800 calculation : HMRC's automatic year-end reconciliation for non-SA taxpayers. Sent typically Aug-Oct following tax year end. P800 may show refund or under-payment. Refunds paid automatically. Under-payments collected via tax code or direct payment. Tax code mismatch : if you have multiple PAYE jobs, only ONE should use PA. Common error: both giving full PA = under-payment surfaces at year-end.

Q: What is the SA302 + how do I get one?

SA302 : HMRC summary document showing your year's income + tax calculation. Used for : mortgage applications (lenders prefer SA302 over SA100 because it's HMRC-authenticated), tax credits applications, mortgage affordability checks, lender income verification. How to get : log into Government Gateway + Self-Assessment account + select tax year + "Get your SA302 tax calculation". Available within 72 hours of SA submission. PDF download for last 4 years. Tax year overview vs SA302 : Tax year overview = single-page summary, shows tax owed/paid. SA302 = detailed multi-page calculation. Lenders typically require BOTH. Pre-2017 returns : SA302 not available online for very old years - request from HMRC by phone 0300 200 3310. Print restrictions : lenders increasingly require electronic SA302 download (PDF) rather than printed - reduces fraud risk. Government Gateway PDF downloads are HMRC-verified. Self-employed + multiple income sources : SA302 shows aggregated income picture - useful for showing total earning capacity to lenders.

Comprehensive UK Self-Assessment guide for 2026/27. Registration 5 October deadline, paper 31 October + online 31 January filing deadlines, 31 July second Payment on Account. Schedule 55 FA 2009 late filing penalty structure (£100 fixed + £10/day + 5% + tax-geared 5-100%), Schedule 56 late payment surcharges, HMRC interest at base+2.5%. Schedule 24 inaccuracy penalties + Schedule 41 failure-to-notify. Appeals process - HMRC internal review + First-tier Tribunal. MTD ITSA phase-in - April April 2026 £50k, April April 2027 £30k, April April 2028 £20k. SA302 mortgage application. PAYE interaction + tax code adjustment. DIY vs accountant decision. Statute - TMA 1970, FA 2009 Sch 55+56, FA 2007 Sch 24, FA 2008 Sch 41.

2026/27 key dates

Date	What	Detail
5 October 2027	SA registration deadline	If you started self-employment, became a landlord, or had untaxed income in 2026/27 you must notify HMRC by 5 October 2027. Late notification = potential failure-to-notify penalty under Schedule 41 FA 2008 (0%-100% of unpaid tax).
31 October 2027	Paper SA return filing deadline	Paper SA100 returns for 2026/27 must reach HMRC by midnight. Late paper filing = automatic £100 fixed penalty even if no tax due.
30 December 2027	Earlier deadline for PAYE coding adjustment	Submit online SA return by 30 December if you want any tax owed under £3,000 collected via next year's PAYE tax code (avoids needing to write a cheque).
31 January 2028	Online SA return deadline + balancing payment + first POA	Online SA100 for 2026/27 must be filed. Pay any balancing tax owed for 2026/27. Pay first Payment on Account for 2027/28 (50% of last year's IT + Class 4 NI bill, excluding Class 2 + CGT).
31 July 2028	Second Payment on Account for 2027/28	Second 50% POA toward 2027/28 tax bill. Combined with January POA = approximately 100% of last year's tax bill paid in advance.
31 January 2029	Final balancing for 2027/28 + first POA for 2028/29	True-up after 2027/28 actual liability calculated. POA may have over- or under-paid.

SA penalty structure

Trigger	Amount	Authority	Notes
Late filing - day 1 (1 February)	£100 fixed	Schedule 55 FA 2009 Para 3	Automatic, even if no tax owed
Late filing - 3 months overdue (1 May)	+ £10/day for max 90 days = £900	Schedule 55 FA 2009 Para 4	Stops accruing at 90 days
Late filing - 6 months overdue (1 August)	+ greater of £300 OR 5% of tax due	Schedule 55 FA 2009 Para 5	Higher of the two
Late filing - 12 months overdue (1 February next year)	+ greater of £300 OR 5% (standard) / 70% (deliberate) / 100% (deliberate + concealed)	Schedule 55 FA 2009 Para 6	Behavioural - higher for deliberate
Late payment - 30 days overdue	5% of unpaid tax	Schedule 56 FA 2009 Para 3	Surcharge
Late payment - 6 months overdue	+ 5% of unpaid tax	Schedule 56 FA 2009 Para 4	Additional 5%
Late payment - 12 months overdue	+ 5% of unpaid tax	Schedule 56 FA 2009 Para 5	Cumulative 15% surcharge after year
Inaccuracy / error	0-100% of Potential Lost Revenue (200% offshore)	Schedule 24 FA 2007	Behavioural bands - careless 0-30%, deliberate 20-70%, deliberate+concealed 30-100%
Failure to notify (5 Oct missed)	0-100% of unpaid tax	Schedule 41 FA 2008	Behavioural - same bands as Sch 24

Penalties cumulate. A 13-month late deliberate filing with £10k tax owed could attract £100 + £900 + greater of £300 or £500 + greater of £300 or £7,000 = potentially £8k+ in penalties on top of the £10k tax + interest.

MTD ITSA phase-in

Making Tax Digital for Income Tax Self-Assessment replaces annual SA filing with quarterly digital submissions for self-employed + landlords above income thresholds.

Effective from	Threshold (gross income)	Estimated additional taxpayers
April 2026	> £50,000	~780,000
April 2027	> £30,000	~1.4 million
April 2028	> £20,000	~700,000 additional

MTD-affected taxpayers must keep digital records + submit quarterly updates via MTD-compatible software (Xero, QuickBooks, FreeAgent, Sage, FTAX, TaxCalc). End-of-period statement at year-end. Final declaration by 31 January following tax year end.

Frequently asked questions

Who must file a Self-Assessment tax return for 2026/27?

Mandatory SA filers: (a) self-employed earning >£1,000 gross (above trading allowance); (b) partner in business partnership; (c) earning >£50,000 with Child Benefit (HICBC trigger); (d) earning >£100,000 from any source (PA taper); (e) gross dividend income >£10,000 (was £2,000 before April 2024); (f) gross savings interest >£10,000; (g) rental income >£2,500 net (after PIM allowable expenses) or >£10,000 gross; (h) foreign income; (i) capital gains above the £3,000 Annual Exempt Amount; (j) HMRC-issued SA notice ("notice to file"); (k) directors of UK Ltd companies (HMRC guidance - though not strict statutory rule); (l) selling shares / property requiring CGT reporting. Voluntary SA: anyone can request to file SA via gov.uk/register-for-self-assessment - useful for claiming reliefs (Gift Aid higher-rate, pension higher-rate, EIS / SEIS / VCT) without waiting for HMRC P800. Penalty for not filing when required: see late filing penalties table above. Plus Schedule 41 FA 2008 failure-to-notify penalty if you also missed the 5 October registration deadline.

How do Payments on Account (POA) work?

HMRC requires advance payments toward your CURRENT year's tax bill based on the PRIOR year's IT + Class 4 NI liability. Trigger: prior year's "balancing payment" (after PAYE deductions) was £1,000+ AND less than 80% of prior year's tax was paid via PAYE / withholding. Calculation: each POA = 50% of prior year's IT + Class 4 NI. Class 2 NI + CGT are NOT included in POA calc. Payment dates: 31 January (1st POA, alongside balancing payment for prior year) + 31 July (2nd POA). Worked example 2026/27 → 2027/28: 2026/27 SA shows £8,000 IT + Class 4 NI. Each POA = £4,000 toward 2027/28. Pay £4,000 on 31 January 2028 (alongside balancing 2026/27 payment) + £4,000 on 31 July 2028. Reducing POA: if you expect 2027/28 income to be SIGNIFICANTLY lower (e.g., maternity leave, retirement, business closure), can request reduced POA via SA303 claim form. Risk: HMRC charges interest if reduced POA turns out to be too low. Overpaid POA: refunded after final return assessment + can offset against next year.

What is Making Tax Digital for Income Tax Self-Assessment (MTD ITSA)?

MTD ITSA replaces annual SA filing with QUARTERLY DIGITAL UPDATES + final-end-of-period declaration. Phase-in by income threshold. April 2026: self-employed + landlords with gross income >£50,000. April 2027: threshold drops to £30,000. April 2028: threshold drops to £20,000 (announced Autumn Budget 2024). Requirements: digital records of all business income + expenses (no manual spreadsheets after April 2026 for affected). MTD-compatible software (Xero, QuickBooks, FreeAgent, Sage etc) submits quarterly updates by month-end of each quarter. End-of-period statement at tax year-end. Final declaration submitted by 31 January following tax year end. Exemptions: digital exclusion (those who genuinely can't use computers - HMRC discretion). Penalties (new MTD-specific regime from April 2026): points-based - each missed quarterly submission = 1 point. 4 points (£200) = first £200 fine. Then £200 per further missed submission. Points expire after 24 months of compliance. Late tax payment penalties: gradually replacing Schedule 56 FA 2009 surcharges with new MTD-aligned regime.

How do I appeal a Self-Assessment penalty?

Two appeal routes. (1) HMRC internal review: written request within 30 days of penalty notice. HMRC officer (different from original) reviews. Free + simple. Statutory basis Section 49 TMA 1970. Common grounds: (a) "reasonable excuse" - bereavement, serious illness, hospitalisation, postal disruption, HMRC system failure, unexpected events outside control; (b) computational error; (c) HMRC errors; (d) special circumstances under Schedule 55 Para 16 FA 2009 (mitigation). NOT reasonable excuse: forgetting deadline, accountant error, lack of money, ignorance of law. (2) First-tier Tribunal (Tax Chamber): if internal review unsuccessful OR you skip review. File appeal within 30 days. Form TS1 from gov.uk. Free + represent yourself OR via tax adviser. Appeal grounds: same as above - reasonable excuse + technical legal disputes. Tribunal can reduce penalties more generously than HMRC internal review. Recent precedent: Perrin v HMRC [2018] UKUT 156 established broad "reasonable excuse" interpretation. Bourne v HMRC [2019] UKUT 92 - "ignorance of law" specifically not a reasonable excuse. Higher tribunals: Upper Tribunal + Court of Appeal for points of law. Rare for SA penalty cases - typically First-tier final.

What is HMRC interest rate on late payments?

HMRC charges interest from the due date (typically 31 January / 31 July) on any unpaid tax. Rate formula: Bank of England base rate + 2.5% (Section 178 FA 1989 + Schedule 53 FA 2009). Current rate (2026): approximately 7%-8% depending on BoE rate movements. Interest accrues daily from day 1 of overdue period - no grace period. Compounded by HMRC system. Late payment surcharges on top of interest: 5% at 30 days + 6 months + 12 months = potential 15% surcharge over 12 months PLUS the interest accrual. Interest is NOT tax-deductible: business interest expense excluded. HMRC repayment interest: when HMRC owes you a refund, lower rate paid (base rate - 1%, minimum 0.5%). Asymmetric. Time to Pay (TTP) arrangements: if you genuinely can't pay, contact HMRC TTP helpline 0300 200 3835 BEFORE the due date. Interest still accrues during TTP but late payment surcharges may be suspended. Online TTP available for SA debts up to £30,000.

When should I file paper SA100 vs online?

Strongly prefer online filing via Government Gateway. Online deadline 31 January 2028 (3 months later than paper). Paper SA100: deadline 31 October 2027. £100 fixed penalty for late paper even if you switch to online later. Some scenarios require paper: trustees of certain non-resident trusts, partnership returns (SA800) for years where partnership has complex foreign elements, certain non-standard claims. Most individuals: online preferred. Free HMRC online service handles most situations. Software alternatives (TaxCalc, FTAX, BTC) for complex returns. Online benefits: HMRC pre-fills employment income from RTI feeds, instant calculation, immediate filing confirmation, easier to amend, refunds processed faster (typically 2-3 weeks vs 6-8 for paper). Don't have Government Gateway? Register at gov.uk/log-in-register-hmrc-online-services. Verification via passport/driving licence/credit history + ~3-7 days for HMRC to send activation code by post. Start the process at least 4 weeks before deadline. HMRC support: 0300 200 3310 SA helpline.

What records must I keep for SA + how long?

Self-employed + partnership: 5 years from 31 January submission deadline (so records for 2026/27 → keep until 31 January 2033). All other SA filers: 22 months from end of tax year (so 2026/27 → keep until 31 January 2029). Statutory basis Section 12B TMA 1970. Records to keep: (a) all business income receipts/invoices with date + payer + amount; (b) all business expenses receipts/invoices; (c) bank statements (separate business account preferred); (d) payslips, P60, P11D, P45 from employments; (e) interest certificates from banks/building societies; (f) dividend vouchers; (g) gift aid declarations; (h) capital gains computations + supporting docs; (i) rental property records (income, expenses, mortgage interest, capital improvements). Digital records OK: HMRC accepts electronic copies. MTD ITSA from April 2026: requires DIGITAL records for affected (>£50k income initially). Manual spreadsheets become non-compliant. Penalties for missing records: £3,000 fine under Section 12B(5) TMA 1970 + likely "best of judgment" assessment by HMRC if records can't substantiate return.

Can I file SA late - what are my options?

If you missed 31 January: file ASAP. £100 fixed penalty already triggered but daily penalties (£10/day) start at 3 months overdue. Filing within first 90 days minimises further penalty accrual. If 3+ months overdue: pay the £100 + accrued daily penalties + file return immediately. Each day of delay costs £10. If 6+ months overdue: penalty £100 + £900 daily (max) + greater of £300 or 5% of tax = potential £1,300+ even before tax-geared penalties. If 12+ months overdue: same as 6 months + additional greater of £300 or 5% (or up to 100% if deliberate). Plus Schedule 24 penalties on tax + Schedule 56 late payment surcharges + interest. Reasonable excuse appeal: see appeal FAQ. Voluntary disclosure: if you've been non-compliant for multiple years, use Digital Disclosure Service (gov.uk/government/news/disclosure-of-tax-and-duty) for structured disclosure with better penalty terms. Don't file blank return to avoid penalty: filing inaccurate return triggers Schedule 24 inaccuracy penalties on top - worse than late filing. Most cost-effective: file accurate return as soon as practicable + appeal penalties with reasonable excuse if available.

How does PAYE interact with Self-Assessment?

PAYE employees have tax + NI deducted at source via tax code (e.g., 1257L). For most, PAYE accounts for full year's tax liability and SA isn't required. SA still needed when: total income from other sources (interest, dividends, rental, self-employed side income) above threshold triggers SA filing; or HICBC applies; or PA taper applies (£100k+ income); or you want to claim higher-rate relief on pension / Gift Aid / EIS / SEIS / VCT. PAYE + SA combined: SA reconciles the WHOLE year's tax position. Any PAYE under-deducted = balancing payment to HMRC. Any over-deducted = refund. Tax code adjustment: if SA shows small under-payment <£3,000, HMRC can adjust NEXT year's PAYE tax code to collect via reduced PA. Avoids one-off cheque. Triggered by 30 December online filing deadline. P800 calculation: HMRC's automatic year-end reconciliation for non-SA taxpayers. Sent typically Aug-Oct following tax year end. P800 may show refund or under-payment. Refunds paid automatically. Under-payments collected via tax code or direct payment. Tax code mismatch: if you have multiple PAYE jobs, only ONE should use PA. Common error: both giving full PA = under-payment surfaces at year-end.

What is the SA302 + how do I get one?

SA302: HMRC summary document showing your year's income + tax calculation. Used for: mortgage applications (lenders prefer SA302 over SA100 because it's HMRC-authenticated), tax credits applications, mortgage affordability checks, lender income verification. How to get: log into Government Gateway + Self-Assessment account + select tax year + "Get your SA302 tax calculation". Available within 72 hours of SA submission. PDF download for last 4 years. Tax year overview vs SA302: Tax year overview = single-page summary, shows tax owed/paid. SA302 = detailed multi-page calculation. Lenders typically require BOTH. Pre-2017 returns: SA302 not available online for very old years - request from HMRC by phone 0300 200 3310. Print restrictions: lenders increasingly require electronic SA302 download (PDF) rather than printed - reduces fraud risk. Government Gateway PDF downloads are HMRC-verified. Self-employed + multiple income sources: SA302 shows aggregated income picture - useful for showing total earning capacity to lenders.

What changes are coming to SA after April 2027 and beyond?

April 2026: MTD ITSA mandatory for self-employed + landlords with >£50,000 gross income. Quarterly updates + EOPS + final declaration replace annual SA. April 2027: MTD ITSA threshold drops to >£30,000. Adds ~1.4 million additional taxpayers. April 2028: threshold drops to >£20,000 (Autumn Budget 2024 announcement). Adds ~~700k more. April 2027 pension reform: defined-contribution pensions enter IHT estate (Finance Act 2025). SA returns may need IHT reporting elements for high-net-worth families. Digital Services Tax shift: gig economy platforms required to report user earnings to HMRC (Section 349 FA 2024 - reporting from January 2024 for 2024 earnings). Reduces SA non-compliance for platform workers. SA penalty regime overhaul: gradually replacing Schedule 55 FA 2009 with points-based MTD penalties. Different surcharge tier structure. Long-term: HMRC roadmap suggests SA may eventually be replaced for most individuals by RTI-driven automatic tax calculation (similar to PAYE), reserving SA for genuinely complex cases. Timeline: 2030s+.

Should I file SA myself or use an accountant?

DIY SA: appropriate for: employees with one source of income + small side income; simple landlord with 1-2 properties; basic-rate taxpayers; people comfortable with HMRC online interface; people with budget <£200-£500. Time investment: 4-12 hours typical for moderately complex return. Accountant recommended: high-rate taxpayers + multiple income sources; landlords with 3+ properties; self-employed with complex income (multiple contracts, foreign earnings, partner in business); investments with EIS / SEIS / VCT claims; capital gains involving share-matching; high-net-worth with trusts / non-dom / international elements; anyone earning >£200k. Cost: £150-£500 for simple SA, £500-£2,000 for complex SA, £2,000+ for HNW. Often pays for itself via missed deductions found by accountant. Bookkeeper alternative: cheaper than accountant (£20-£40/hour vs £80-£200) - good for record-keeping then DIY return submission. Tax software: between DIY + accountant - FTAX (£35), TaxCalc (£70-£170), Andica (£45-£170). Helps catch common mistakes. HMRC free online: covers most simple cases - no need to buy software for standard SA100.