From understanding who must file, to registering, keeping records, and paying your bill. Everything you need to navigate HMRC's Self Assessment and the incoming Making Tax Digital for Income Tax rules.
Self Assessment is the system HM Revenue and Customs (HMRC) uses to collect Income Tax. Tax is usually deducted automatically from wages, pensions, and savings. But if you have other income, you must report it in a tax return.
If you are employed and only owe a small amount of tax (under £3,000) from other sources, HMRC can often "code it out" by adjusting your PAYE tax code. However, you must submit your online return by 30 December to request this.
The UK Tax Year runs from 6 April to 5 April the following year. Missing these dates leads to automatic penalties.
You must tell HMRC and register for Self Assessment by 5 October following the end of the tax year you need to file for.
If you choose to submit a paper tax return (SA100) instead of filing online, HMRC must receive it by midnight on 31 October.
This is the final deadline. You must submit your online tax return and pay your balancing payment (and first Payment on Account for the next year, if applicable) by midnight.
If your tax bill was over £1,000, your second advance payment towards your current year's bill is due.
These are two advance payments towards your tax bill (due 31 Jan and 31 July) required if your previous year's tax bill was over £1,000. They are calculated as half of your previous year's tax bill. You can ask to reduce them if you know your income has dropped, but reducing them too far incurs interest charges.
Before you can file, you need a UTR (Unique Taxpayer Reference) and an active HMRC online account.
Register online via GOV.UK. Are you self-employed? Use the sole trader route. Just have property or investment income? Use the SA1 form route. Joining a partnership? Form SA401 is required.
Provide your National Insurance number and details. HMRC will post your 10-digit UTR number to you. This can take up to 10-15 working days, so don't leave it until January.
Use your Government Gateway or GOV.UK One Login to access your personal tax account. You'll receive an activation code in the post to link your UTR to your account securely.
You must declare all of your income, not just the income that triggered the SA requirement.
Use your P60, P45, and P11D to report PAYE salary, company cars, medical insurance, and claim allowable professional fees or union subscriptions.
Calculate your income minus allowable expenses. This also calculates your Class 2 and Class 4 National Insurance.
Report rent received minus property expenses. Note that residential mortgage interest relief is now restricted and claimed as a basic rate tax reduction.
Include bank interest and company dividends. You have personal savings and dividend allowances before tax is applied, often at different tax rates.
Report overseas earnings or rental income. You can usually claim Foreign Tax Credit Relief so you aren’t taxed twice on the same money.
Higher-rate taxpayers must use their return to claim the extra 20% or 25% tax relief owed on personal pension contributions and Gift Aid charity donations.
Most people file online directly via HMRC's portal, but if you have commercial software, bank feeds can speed up the process. A common mistake is omitting tiny bank interest amounts or accidentally claiming personal costs as business expenses.
Fact: You must retain your records. Self-employed and landlords must keep them for 5 years after the 31 January deadline. Others generally need to keep them for 22 months.
HMRC accepts Faster Payments, online banking, and Direct Debit. Credit cards have fees and personal ones can't be used. If you can't pay the full amount, you can proactively set up a Time to Pay arrangement online to spread the cost and avoid late payment penalties (though interest still applies).
Filing late triggers an automatic £100 penalty, even if you owe zero tax. After 3 months, daily penalties of £10 apply. Paying late incurs further percentage-based penalties and daily interest. If you make a mistake, you have a 12-month window to amend your return without penalty, provided it wasn't a deliberate inaccuracy.
The biggest change to taxation in decades. The annual paper/online Self Assessment return is being phased out for certain groups in favor of digital reporting.
Construction workers have 20% or 30% tax deducted at source by contractors. You put these deductions on your SA return. If they exceed your total tax bill, HMRC refunds the difference.
Directors don't automatically need to file unless they have other untaxed income or dividend income that triggers the requirement under standard dividend tax rules.
If you're non-resident but have UK income (like UK property), you must file. You cannot use HMRC's free online software for this; you must use commercial software or file a paper SA109 routing.
No. The UK utilizes independent taxation. You and your spouse must file completely separate Self Assessment tax returns based on your individual incomes. However, you can transfer a small amount of Personal Allowance using the Marriage Allowance if eligible.
HMRC treats cryptocurrency similarly to shares. Gains from trading crypto must be reported on the Capital Gains pages (SA108) if they exceed the annual exemption. If you are "mining" or being paid in crypto, it is usually treated as Income and goes on the main return.
By default, HMRC assumes property owned jointly by spouses is split 50:50. If you actually own it in unequal shares, you must submit a Form 17 to HMRC along with a declaration of trust to be taxed on your actual share.
Yes. If your self-employed profits are below the Small Profits Threshold, you might not automatically earn a qualifying year for your State Pension. You can check a box on your return to voluntarily pay Class 2 NI to protect your state pension record.
Yes. You can appoint an accountant/agent who can file on your behalf. They will send a digital authorization request to your HMRC account. You can also appoint a friend or family member as a "trusted helper" via GOV.UK, giving them access to manage your tax digitally.