Self Assessment is much easier when you do the boring part first: getting your documents together. If you start the return without the right info to hand, you’ll end up guessing, missing income, or forgetting expenses — and that’s how people get nasty surprises (or spend hours redoing everything).

This checklist is designed to help you gather what you need before you log in. It’s written for UK sole traders, landlords, directors, contractors, and anyone with income outside PAYE.

And yes, there are deadlines to keep in mind. For online returns for the 2024/25 tax year, the deadline is 31 January 2026 (23:59), and late filing can trigger an automatic £100 penalty. 

1) Your “starter pack” (get these first)

These are the essentials you’ll nearly always need, no matter how you earn your income:

• National Insurance number
• UTR (Unique Taxpayer Reference) if you’re already registered for Self Assessment
• Government Gateway login details
• Your address history (if you’ve moved during the tax year)
• Your bank details (useful if you’re due a refund)
• Any HMRC letters you’ve received about your tax code, payments on account, or queries

If you’re doing this for the first time, remember that registration deadlines can apply (HMRC has historically used 5 October after the end of the tax year as the registration deadline in many cases). 

If you want help getting set up properly (especially if you’re self-employed, a landlord, or you’ve got multiple income streams), start with Tax Return.

2) Employment income (PAYE) checklist

Even if you’re mainly self-employed or a landlord, you might still have PAYE income — and HMRC will expect it to be included correctly.

Gather:

• P60 (end-of-year summary from your employer)
• P45 (if you left a job during the year)
• P11D (if you had taxable benefits like a company car or private medical insurance)
• Details of any expenses paid by your employer
• Details of company benefits and reimbursed expenses (if not covered clearly in your P11D)

HMRC’s guide explains what P45, P60 and P11D forms are used for and how to replace them if needed. 

If you run payroll for your own company (or employ staff), your payroll paperwork matters too. It’s worth keeping everything aligned with Payroll Services.

3) Self-employment (sole trader) income and expenses checklist

If you’re a sole trader, your return is only as good as your records. Don’t rely on “rough totals” unless you enjoy stress.

Income to gather

• A list of sales invoices (or a sales report from your software)
• Bank statements (ideally business account statements)
• Cash income records (if you take cash)
• Any platform statements (e.g., marketplaces, booking platforms, payment processors)
• Notes on refunds and chargebacks (so turnover isn’t overstated)

Expenses to gather

Collect invoices/receipts for:

• stock/materials and direct costs
• tools and equipment (flag bigger items, because they may be treated differently)
• phone and internet (business proportion)
• software subscriptions
• travel (fuel, train, parking) and mileage logs
• marketing costs (ads, printing, website)
• professional fees (insurance, legal, accountancy)
• use of home as office (if relevant)
• business loans/finance interest (business portion)

This is where good bookkeeping saves you hours. If your records are scattered, get a clean system in place with Book Keeping and (if you’re on cloud software) Quickbooks Accountants.

If you’re not sure what a “good” sole trader setup looks like, Sole Trader Accounting is a sensible starting point.

4) Landlord and property income checklist

If you’re a landlord, the biggest mistake is treating property income like it’s just “rent in, bills out”. HMRC expects proper totals and clear categorisation.

Gather:

Income

• rent schedule (monthly rent received)
• letting agent statements
• bank statements showing rent payments
• details of any arrears, write-offs, or refunds

Expenses

• letting agent fees
• repairs and maintenance invoices (keep notes on what was done and when)
• landlord insurance
• ground rent/service charges (if leasehold)
• council tax/utility bills (if you covered them during void periods)
• safety certificates and compliance costs (as applicable)
• legal/professional fees related to the rental business

If you want a simple way to organise rental income and expenses, use Guide to Rental Income and Expense.

If you’re considering using a company for property (or you already do), that’s a different setup and can change what information you need. Read How To Set Up a Buy-To-Let Company.

5) Limited company directors: what to gather

If you run a limited company, your Self Assessment is often tied to how you pay yourself.

Gather:

• director salary details (from payroll records/P60)
• dividend vouchers and dividend dates/amounts
• details of any director’s loan movements (money you put in or took out outside salary/dividends)
• details of any benefits provided by the company (P11D, etc.)
• any other personal income outside the company

If you’re not sure whether you’re taking income in the most sensible way, speak to an accountant who deals with directors every day. Start with Limited Company Accountants.

You might also find it helpful to understand the wider picture of what support sits around your return in Company Accounts.

6) Savings, interest, and investment income checklist

These are the areas people often forget because they feel “small” — until HMRC data matches them and you get a letter.

Gather:

• bank/building society interest certificates or annual summaries
• statements for fixed-term savings accounts
• dividend statements (shares, funds, investment platforms)
• UK or overseas interest/dividend summaries (if applicable)

If you have a lot of small accounts, pull the annual tax summary or year-end statement from each provider rather than trying to piece it together month by month.

7) Capital gains checklist (if you sold assets)

If you sold shares, crypto, a second property, or other assets, you may need capital gains information.

Gather:

• purchase and sale contract notes (shares/investments)
• disposal proceeds and acquisition cost
• dates of purchase and sale
• platform transaction history (especially if there were multiple buys/sells)
• fees and charges (broker fees can matter)

If property is involved, keep completion statements (purchase and sale) and any evidence of qualifying costs.

8) Pension contributions and Gift Aid checklist

These often reduce your tax bill — but only if you include the right figures.

Gather:

• personal pension contribution statements (and dates paid)
• workplace pension details if you made additional contributions
• Gift Aid donation records (charities can provide annual summaries)

Even if you’re not “doing tax planning”, it’s worth getting these right so you don’t overpay.

9) Student loan, Child Benefit, and other “extras” people miss

These don’t apply to everyone, but when they do apply, they really matter.

Gather:

• student loan plan type and any repayments shown on payslips/P60
• Child Benefit information if you or your partner may be affected by the High Income Child Benefit Charge
• any taxable state benefits or support payments (where relevant)
• details of side income (ad-hoc work, online selling, affiliate income, etc.)

If you’re unsure whether something needs to be declared, it’s usually safer to ask before you submit.

10) If you pay on account, gather your HMRC payment history

A lot of people get confused because they think they’re paying “twice”. Payments on account can mean you owe:

• a balancing payment for the year just ended
• plus a payment on account towards the next year

The Self Assessment deadline page explains what you need to submit and by when, and it’s worth checking that you’re looking at the right year. 

If you’re struggling to pay, HMRC has promoted support options like Time to Pay in its guidance and media coverage, but don’t leave it to the last minute — you normally need to file first. 

11) Your final “before you press submit” checks

Once you’ve gathered everything, do a quick sense-check:

• Do your totals broadly match your bank deposits (allowing for transfers/loans)?
• Have you included all income sources, not just your main one?
• Are big expenses backed by invoices/receipts?
• If you’re self-employed or a landlord, do your figures feel consistent with last year (or is there a clear reason they changed)?
• Have you allowed time to fix missing paperwork before 31 January (to avoid the £100 late filing penalty)? 

If you want more support beyond the return itself — such as ongoing reporting, tax forecasting, and keeping your records tidy through the year — have a look at Financial Reports and the full Services list.

And if you’re not sure which category you fit into, check Who We Help.

Next steps

If you want your Self Assessment done properly — without last-minute panic, missing documents, or overpaying tax — Asmat & Co can handle it with you (or for you) and keep your records organised for next year too. Get in touch via Contact Us and we’ll help you put a simple checklist and process in place that fits your income, whether you’re self-employed, a landlord, a director, or all 3.