Self Assessment Basics
Start here if you are new to Self Assessment. Learn what it is, who needs to file, and what counts as taxable income.
Articles
What is Self Assessment?
Self Assessment is the system HMRC uses to collect income tax from people whose income is not taxed at source. Here is what it means and how it works.
What is a UTR number and how do you find yours?
What a UTR number is, who gets one and when, how long it takes to arrive, where to find a lost UTR, and how it differs from your National Insurance number and a company UTR.
Form 64-8: how to authorise an accountant to deal with HMRC
What form 64-8 is, when the online authorisation code or link is used instead, how long it takes, and how to remove or change your agent.
Who needs to file Self Assessment?
Sole traders, landlords, company directors, and high earners. A clear checklist to see if you are in scope.
How to contact HMRC
Find the right HMRC helpline, postal address or online route for your tax question, refund or suspicious message.
HMRC online accounts: personal tax account, Government Gateway and logins
Find the right HMRC account, recover your Government Gateway user ID and follow official GOV.UK links for personal and business tax services.
Tax Over £100k: The 60% Tax Trap
How the Personal Allowance taper creates an effective 60% marginal tax rate between £100,000 and £125,140, and the ways to reduce it.
Filing First Self Assessment SA100
Step-by-step guide to filing your first UK Self Assessment return (Form SA100): UTR registration, supplementary pages, records, and 31 January deadline.
Self Employed Student Loan Guide
How student loan repayments are calculated on Self Assessment for self-employed individuals and company directors. 2026/27 thresholds (Plan 1, Plan 2, Plan 4, Plan 5, Postgrad).
Self-employed maternity and sick pay: what you can claim
What self-employed people can claim for maternity and sickness in 2026/27: Maternity Allowance, why Statutory Sick Pay does not apply, ESA, Universal Credit and Class 2 National Insurance.
Is PIP taxable? Tax rules for Personal Independence Payment
PIP is a tax-free state benefit: you do not pay tax on it or declare it on a Self Assessment return. How it sits alongside Carer's Allowance, and which state benefits are taxable.
HGV driver meal allowance and overnight subsistence rates
HMRC's lorry driver overnight rate (£34.90, or £26.20 with a sleeper cab), the £5, £10 and £25 day meal rates, and how employed and self-employed drivers claim.
Self-employed mileage allowance: 2026/27 rates
HMRC mileage rates guide for self-employed and directors: 2026/27 55p/mile rate, simplified mileage vs actual expenses, travel logs, and limited company AMAP claims.
Working from home tax relief: 2026/27 rules
Employee working from home tax relief has ended for 2026/27. Understand backdated claims, employer payments and self-employed use of home expenses.
The £1,000 trading allowance: how it works
How the £1,000 trading allowance works: full relief if your gross trading income is £1,000 or less, partial relief above that, who cannot use it, and when you still need to register for Self Assessment.
How to find your National Insurance number
Find your National Insurance number on documents or online, recover a lost number and get a letter confirming it.
What does tax code 0T mean? (UK 2026)
0T means no Personal Allowance is being applied at that income source. Learn what it means, why it can be used and how to check it with HMRC.
What does tax code 1257L mean? (UK 2026/27)
1257L is the usual 2026/27 code for most people with one job or pension. Learn what the number and letter mean and when to check it.
Budget 2026: what it means for business owners, landlords and savers
The 28 October 2026 Budget in plain English. Higher tax on rental and savings income, a £3,000 Trading Allowance, BADR halved, a new 10% Founders' Relief and capital allowance changes.
UK tax thresholds 2026/27: the complete reference
Every threshold that decides how much tax you pay in the 2026/27 UK tax year. Income tax bands, National Insurance, tax-free allowances, with the figures HMRC uses.
Scottish income tax bands 2026/27
Scotland's income tax bands, rates and thresholds for 2026/27, with a band-by-band salary example and a comparison with the rest of the UK.
The 40% tax bracket: when you pay it and how to plan around it (UK 2026/27)
40% income tax starts when your income goes over £50,270 in 2026/27 (England, Wales and Northern Ireland). You pay 40% only on the slice above that, and 45% starts at £125,140. Scotland sets its own bands.
Emergency tax code: W1, M1, X and NONCUM (UK 2026/27)
Emergency tax-code markers W1, M1, X and NONCUM explained: what they mean, where to check your code and what to do after a job change.
Check your HMRC tax refund: P800 letters explained
How to check whether HMRC owes you a tax refund, what a P800 tax calculation letter says, how to claim it online or by cheque, and how to avoid refund scams.
Self Assessment deadlines 2026/27: every key date and what happens if you miss them
The full Self Assessment deadline calendar for the 2025/26 tax year (filed in 2026/27): registration by 5 October 2026, paper returns by 31 October 2026, online filing and payment by 31 January 2027.
The UK personal allowance 2026/27: what it is, what you keep tax-free, and when you lose it
The personal allowance is £12,570 for 2026/27. Income up to this amount is tax-free. The allowance tapers away above £100,000 and disappears entirely at £125,140.
Marriage Allowance explained: who can claim and how
How Marriage Allowance works in 2026/27: who can transfer £1,260 of their Personal Allowance, how it cuts the other partner's tax by up to £252, and how to apply, backdate, cancel and handle Self Assessment.
How much tax do you pay in the UK? Take-home pay at every salary (2026/27)
Exactly how much income tax and National Insurance you pay on £20k, £30k, £50k, £60k, £80k, £100k and £150k salaries in 2026/27, with monthly take-home pay numbers.
UK National Insurance rates and thresholds 2026/27: a complete guide for employees, the self-employed, and employers
Employee NI is 8% above £12,570 and 2% above £50,270. Self-employed Class 4 is 6% / 2% on the same bands. Class 2 is voluntary in some cases. Full rate table and worked examples.
Voluntary National Insurance contributions: who can pay
Who can pay voluntary National Insurance, the difference between Class 2 and Class 3, the 2026/27 weekly rates, the six-year deadline and how to check if filling a gap is worthwhile.
UK dividend tax 2026/27: rates, allowance, and how directors should take income
Dividend tax rates for 2026/27 are 10.75%, 35.75% and 39.35% above the £500 dividend allowance (basic and higher rates raised 2pp from 6 April 2026). Worked examples for limited company directors, the optimal salary vs dividend split, and why dividends still beat salary.
UK Capital Gains Tax 2026/27: rates, the £3,000 allowance, and the 60-day property reporting trap
Capital Gains Tax rates for 2026/27 are 18% on gains within your basic rate band and 24% above it. This applies to residential property and other assets. The annual allowance is £3,000, and Business Asset Disposal Relief is 18%.
IR35 explained for UK contractors: inside vs outside, CEST, and what 'inside' actually costs you
IR35 (off-payroll working) decides whether a contractor working through a PSC is treated as employed or self-employed for tax. The rules, who decides, what 'inside IR35' costs in pounds, and the small company exemption.
Who actually needs to file a Self Assessment return?
Anyone whose tax cannot be fully collected through PAYE. The common triggers: self-employment, rental income, dividends beyond the allowance, a company directorship with untaxed income, the High Income Child Benefit Charge, Capital Gains to report, or foreign income. Employment income alone, taxed through PAYE, does not put you in Self Assessment.
The test is untaxed income, not size of income. A £3,000 rental profit puts you in; a £300,000 salary on PAYE alone does not.
What the process looks like
Register once with HMRC (by 5 October after the end of the first tax year you need to file for) and you receive a Unique Taxpayer Reference. Each year you then report all your income for the tax year, 6 April to 5 April: employment from your P60, plus every untaxed source. HMRC's calculation nets off tax already paid and produces the bill.
File online by 31 January, pay by the same date. That is the whole machine; everything else is detail.
What to declare: everything, then let the reliefs work
The return wants all of it: employment, self-employment, rent, dividends, interest, pensions, gains, foreign income. Declaring income that turns out to be covered by an allowance costs nothing; omitting income that was not covered is where penalties live.
The allowances do real work (personal allowance, dividend allowance, personal savings allowance, trading and property allowances), but they apply through the return, not instead of it.
Where it goes wrong, and our standard
The classic failures are administrative: registering late, filing in January from a shoebox, and discovering payments on account the day the bill arrives. None of them are tax problems; all of them are record problems.
RR clients run through Compliance Vault™: records maintained year-round, the return prepared early from the Evidence Pack, and the January date reduced to a payment reminder from Deadline Lock.
Frequently asked questions
I'm employed and do a little freelancing. Do I need to file?
Once gross self-employment income passes the £1,000 trading allowance, yes. Register and file, even though your job is fully taxed under PAYE. Below £1,000 the trading allowance usually covers it with no return needed for that alone.
Do company directors automatically have to file?
No. Directorship alone does not require a return if all your income is taxed at source. In practice most director-shareholders take dividends, which do trigger filing once they pass the allowance. If HMRC has issued you a notice to file, you file regardless.
What is a UTR and where do I find it?
Your Unique Taxpayer Reference: a ten-digit number issued when you register for Self Assessment. It is on HMRC letters and in your online tax account, and you need it to file. Lost it? It is retrievable through your HMRC account rather than by re-registering.
Can HMRC just take the tax through my tax code instead?
Sometimes. Smaller Self Assessment balances can be collected through a PAYE tax code if you file by 30 December and meet the conditions. It spreads the cost interest-free across the following year, which for employed filers is often worth having.