Everything you need to fill out and file your Self Assessment tax return

Thinking about completing your Self Assessment tax return soon? To help you prepare and save some time, here’s a list of everything that you’ll need to have to hand before you get started.

Unique Taxpayer Reference (UTR)

When you first register for Self Assessment, or when you set up a limited company, you’ll receive a unique UTR number. It’s the 10-digit code you’ll see any letters from HMRC, such as your Notice to Complete a Tax Return.

Government Gateway ID

When you register for Self Assessment you’ll also receive a 12-digit Government Gateway ID, also called your User ID. Keep this safe! If you lose it it can take a while to receive a new one and you’ll need it to access your HMRC online account.

Activation code (for your first Self Assessment)

If this is your first Self Assessment you’ll have received an activation code in the post shortly after you set up your HMRC tax account online using your Government Gateway ID. You need to enter this code in order to complete registration for Self Assessment, get access to your tax account and to file your tax return online.

Be aware that the deadline for registration was last October so if you still need to do this, you’d better hurry! It can take a while for HMRC to send out the relevant information, especially after the registration deadline.

If you filed a tax return last year then don’t worry, HMRC will already be expecting another one from you this year (unless they’ve sent you a letter advising you they don’t want one) and your account will still be active.

National Insurance number

Your National Insurance number is used to record any tax or National Insurance Contributions (NICs) against your name. You can find it on most letters about tax, pensions or benefits and on any payslips or P60s from previous or current employers.


If you’re a sole trader or partner in a partnership or LLP, you need to add up all your invoices to calculate your income for the year.

Unless you’re using the cash basis of accounting, remember that you pay tax when you issue an invoice, not when you receive payment. For example, if you issued an invoice in the 2021/22 tax year that wasn’t paid until the 2022/23 tax year, you should still include this amount in your 2021/22 Self Assessment.

Income from other jobs (dig out your P60!)

If you were paid a salary by another employer you need to know how much you received, how much was taxed at source and the employer’s PAYE tax reference. These figures can all be found on your P60 so make sure you have this form to hand.

If you received any benefits from your employer in addition to your salary, including expenses that were paid back to you, you also need to enter these figures. You can find this information on your P11D form.


If you’re a limited company director, you need to know how much salary was due to you from your business. Bear in mind that you must pay tax on any salary that was due in the tax year you're filing for, regardless of whether it was actually paid.


For limited company directors who declared dividends in the tax year, you need to include this information on your tax return – even if the dividend wasn’t paid until after the end of the tax year.

You also need to declare dividends payments received in the tax year from companies other than your own.

If you’ve received dividends from a company outside the UK that amount to more than £300, this information needs to go in the “foreign income” section of your tax return.

Bank interest

You need to declare any interest received from bank accounts, so you’ll need to collect all of your bank interest certificates ahead of time.

Exceptions to this are interest from ISAs, which are tax-free accounts, and interest on a limited company’s business account, which will be declared on the company’s Corporation Tax Return.

If your bank account is a joint account you only need to declare half of the interest received in the tax year.

Income from rental properties

If you’ve received income from renting out a property, you need to include this as part of your your tax calculation.

Income from trusts

Similarly, you need to declare income from trusts in order to pay the correct amount of tax.


Your allowable expenses for the year can be used to reduce your tax bill if you’re a sole trader or in partnership. Find out what you can claim in our A-Z guide of expenses.

Pensions and benefits

You need to declare your overall income from the State Pension and any private pensions if you have received any payments. If you have a private pension, your pension provider will usually tax the payments before they pay them out and send you a P60 detailing the amounts that were deducted.

You also need to declare any state benefits you’ve received, such as Job Seekers Allowance (JSA) and Incapacity Benefit.

Student loan repayments

For student loans, you need to know what plan you’re on and how much of the loan you repaid in the tax year. Check this guide to paying back your student loan when you’re self employed to find out more.

Donations to charities under Gift Aid

Donations you make under Gift Aid are eligible for tax relief. You can even claim relief on donations you’ve made after the end of the tax year up to the date you send your return - but only if you submit your return by the 31st January deadline.

Time to get going!

If you’re already using FreeAgent, a lot of the information needed to complete your tax return will be ready and waiting in your account from data you’ve entered throughout the year. When you come to file as a sole trader, parts of the Self Employment form will already be filled in. If you’re a sole trader or a director of limited company you can also submit your tax return directly to HMRC from the software.

Find out more about filing your tax return online using FreeAgent.

Disclaimer: The content included in this guide is based on our understanding of tax law at the time of publication. It may be subject to change and may not be applicable to your circumstances, so should not be relied upon. You are responsible for complying with tax law and should seek independent advice if you require further information about the content included in this guide. If you don't have an accountant, take a look at our directory to find a FreeAgent Practice Partner based in your local area.