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Written by Brad Askew
Legal Tech Founder
Civil & Commercial Law background · Founder of LegalDocuments.co.uk
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Updated April 2026 · England & Wales
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BA
Written by Brad Askew Legal Tech Founder
Civil & Commercial Law background · Founder of LegalDocuments.co.uk
Updated May 2026
·
England & Wales
Dealing with HMRC is something nearly everyone in the UK has to do at some point, whether you're starting a new job, filing a tax return, or sorting out your National Insurance. The problem is that the sheer number of forms, codes, and reference numbers can feel overwhelming, especially when you're not sure which one applies to your situation.
I've put together this guide to walk you through the forms most people run into, what each one does, and when you're likely to need it. It won't replace a conversation with an adviser if your circumstances are complicated, but it should give you a solid grounding so you can approach HMRC with more confidence and less guesswork.
What this document is
HMRC forms are the paperwork (increasingly digital) that the UK tax authority uses to record, collect, and verify information about your income, tax, and contributions. They cover a wide range of scenarios: leaving a job, starting one, reporting self-employed earnings, claiming back expenses, paying inheritance tax, registering for VAT, and much more.
Each form has a specific purpose and a specific audience. Some are issued to you by your employer, some you request from HMRC directly, and others you complete and submit yourself through the gov.uk portal. Getting the right form to the right place at the right time matters because late or incorrect submissions can trigger penalties, interest charges, or delays in refunds and benefits.
Understanding which forms apply to your situation is the first step toward staying on top of your tax affairs and avoiding unnecessary hassle. This guide focuses on the most common forms individuals deal with, rather than the more specialist ones used by larger businesses or estates.
How to use this document
01
Work out which form you actually need. Before anything else, identify what you're trying to achieve. Are you leaving a job, starting one, filing a return, or claiming something back? Each task has its own form, and picking the wrong one wastes time and can cause problems later.
02
Gather your reference numbers and paperwork. You'll usually need your National Insurance number, Unique Taxpayer Reference (UTR) if you have one, employer PAYE details, and records of income and expenses. Having these ready before you start makes the process far smoother and reduces the risk of errors.
03
Complete the form accurately and honestly. Read each question carefully and use the notes or guidance provided on gov.uk. If a section doesn't apply, follow the instructions rather than leaving it blank. Mistakes can delay processing or flag your submission for further review.
04
Submit before the deadline. Different forms have different deadlines, and some carry automatic penalties if you're late. For Self Assessment, for example, the online filing deadline is typically 31 January following the tax year. Check the specific deadline for your form on gov.uk.
05
Keep copies and track your submission. Save a copy of anything you submit, along with confirmation receipts. HMRC can ask you to produce records going back several years, so organised record-keeping now can save you real stress later if questions arise.
Common questions
QWhat is a P45 and when will I get one?
A P45 is the form your employer gives you when you stop working for them. It shows how much you've earned and how much tax and National Insurance has been deducted in the current tax year. You'll typically hand part of it to your next employer so they can apply the correct tax code and avoid putting you on emergency tax.
QWhat's the difference between a P60 and a P45?
A P60 is an annual summary issued by your employer at the end of each tax year (5 April), showing your total pay and deductions for that year in that job. A P45 is issued only when you leave a job. You'll receive a P60 every year you're employed on 5 April, but a P45 only on departure.
QDo I need to complete a Self Assessment tax return?
You generally need to file a Self Assessment if you're self-employed, a company director, a landlord, or have untaxed income above certain thresholds. HMRC will usually tell you if they expect one, but the responsibility to register sits with you. If you're unsure, check the Self Assessment criteria on gov.uk.
QWhat is a P11D form used for?
A P11D reports benefits in kind and expenses that an employer has provided to an employee or director, such as a company car, private medical insurance, or interest-free loans. Your employer prepares and submits it to HMRC, and you should receive a copy to help you complete your own tax affairs accurately.
QWhat happens if I file an HMRC form late?
Late filing can trigger automatic penalties, and further charges may apply the longer the delay continues. Interest may also accrue on any unpaid tax. The exact amounts change over time, so check gov.uk for the current figures. If you have a genuine reason for being late, you can sometimes appeal the penalty.
QHow do I correct a mistake on a form I've already submitted?
For Self Assessment, you can usually amend a return within 12 months of the original filing deadline through your online account. For other forms, the process varies: sometimes you contact HMRC directly, sometimes you submit a corrected version. Acting quickly once you spot the error generally gives you the best outcome.
QCan I submit HMRC forms online?
Most HMRC forms can now be completed and submitted through your Personal Tax Account or Business Tax Account on gov.uk. Some specialist forms still require paper submission or post. Online filing is usually faster, gives you instant confirmation, and reduces the risk of forms going missing in the post.
BA
Brad Askew Legal Tech Founder
Brad has a background in civil and commercial law and founded LegalDocuments.co.uk to make clear, reliable legal information accessible to everyone. This site is not a law firm and does not provide regulated legal advice.
Legal disclaimer
This article is for general information only and does not constitute legal advice. We are not solicitors. For advice on your specific situation, please consult a qualified solicitor.
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