Self Assessment 2025/26: a practical preparation checklist

1. Start with the correct tax year and dates

The 2025 to 2026 tax year ran from 6 April 2025 to 5 April 2026. The usual online filing and payment deadline is 31 January 2027, while the usual paper filing deadline is 31 October 2026. The notification date for people required to register for that year was 5 October 2026. If that has been missed, check the registration and payment position promptly rather than assuming every deadline moves. HMRC explains the exceptions and late-registration arrangements in its Self Assessment deadline guidance.

Create a short calendar containing the relevant filing route, payment dates, document requests and your own review meeting. Put internal deadlines ahead of the statutory dates. A return that depends on a missing interest statement or unresolved business transaction needs time for questions. Planning the preparation stages also avoids treating a payment deadline as the date to start collecting information.

2. Establish why you need a return

A return may be required because of self-employment, partnership income, untaxed income or another aspect of your tax position. Being a company director does not, by itself, answer the whole question. Neither does having tax deducted from one income source. Review your circumstances against HMRC's guidance on who must send a return, and discuss any notice to file with your adviser.

Write down what changed during the year. You may have started a business, received rental income, changed employment, sold an asset or received overseas income. A list of changes gives the accountant a better starting point than a folder labelled “tax”. It also helps identify documents that would otherwise be missing. Do not decide that an unfamiliar receipt is irrelevant simply because it does not resemble your usual trading income.

If you previously filed but believe a return is no longer needed, check how that position should be confirmed. Leaving the process unfinished can create avoidable uncertainty. Keep the relevant HMRC correspondence with your preparation file.

3. Keep access and identity information separate from financial records

Before work begins, locate your Unique Taxpayer Reference, National Insurance number and recent HMRC letters. Check that the name and contact information used for the engagement are current. These details help identify the right taxpayer and tax year, but they should be shared through the arrangements agreed with the practice.

You should not send account passwords through an enquiry form or include them in a spreadsheet of expenses. An accountant's authorisation to act is a separate process from possessing your login credentials. Ask what is needed and how it should be supplied. This keeps the first conversation focused on the work while providing a sensible route for confidential documents.

If you cannot find a reference or have trouble accessing your account, flag the issue early. Treating it as a preparation task gives you time to resolve it. Waiting until the final review can leave an otherwise organised return delayed by an administrative problem.

4. Build an income map before adding up figures

List each source of income separately, even where payments reach the same bank account. Possible headings include employment, self-employment, property, savings, dividends, pensions and other income requiring discussion. Under each heading, identify the documents available, the period covered and the person who can supply anything missing.

This map is useful because a bank account is a collection of movements, not a complete tax explanation. A transfer from another account, repayment of a loan or refund may look like income without representing the same thing as a customer payment. Equally, an income source may have supporting documents that do not appear clearly in the bank description.

For a business owner with several activities, avoid combining everything into one unexplained total. Separate records help the accountant understand the underlying activities and ask specific questions. The objective is an organised evidence trail, rather than a large quantity of documents with no indication of what they represent.

5. Gather employment and pension documents

If you have employment income as well as a business, collect the relevant year-end or leaving documents and information about benefits that need consideration. Keep payroll paperwork for different employers separate. If you changed jobs, make a simple note of the dates and explain which documents relate to each role.

Pension income and contributions should also be identified rather than left within a general bank export. The treatment of different arrangements depends on the facts, so provide the underlying statements and discuss them. A clear description of what a payment represents is more useful than a guess about how much tax relief it produces.

When a document appears inconsistent with your own records, retain both and flag the difference. Do not overwrite the official figure to make the file look tidy. A question list allows the accountant to resolve the issue while preserving the original evidence. Small discrepancies can often be understood more quickly when the background has not been lost.

6. Organise the business records around transactions

For self-employment, bring together sales information, purchase invoices, receipts, bank statements and the records used to track the business. HMRC describes the core evidence in its business records guidance. A practical filing system should let you move from a figure in the accounts back to the transaction and its explanation.

Group records by period and source. A monthly bank statement folder can sit beside sales and purchase records for the same month. Use filenames that distinguish suppliers and document dates. A credit note should remain connected to the invoice it adjusts, instead of disappearing into a folder of refunds.

For wholesalers, include information about stock and customer or supplier balances where relevant to the accounts. Describe how goods are received, recorded and sold. The accountant needs to understand the record system before deciding which year-end information is necessary. A spreadsheet total alone may not explain whether it represents purchases, goods held or the cost associated with sales.

7. Reconcile the bank without treating every movement as income

A bank reconciliation is a check that the recorded transactions and the statement balance connect. It is also an opportunity to identify unexplained movements. Customer receipts, supplier payments, transfers, finance repayments and money introduced by the owner should be considered in context.

Prepare a list of items you cannot identify, including the date, amount, bank reference and any information already found. This saves the accountant from asking the same basic questions repeatedly. It is better to mark a transaction as unresolved than to place it in a convenient category merely to finish the spreadsheet.

If you use more than one bank account, payment processor or card, explain that from the start. A complete reconciliation cannot be built from only the easiest account to download. For a wholesale business, payment allocation matters too: one customer receipt may settle several invoices, while one supplier payment may include credits. Keep those connections visible.

8. Describe expenses before deciding their tax treatment

Business spending is not automatically deductible in every circumstance. The nature of the cost, business purpose and any private element need consideration. Use HMRC's expenses guidance as an introduction, then provide enough information for the actual transaction to be reviewed.

Describe unusual purchases in ordinary language. Explain what was bought, why it was needed, whether it is still used and whether it has a private role. For costs shared between business and personal use, retain the basis of any allocation so it can be discussed. Do not add a blanket percentage to every category without supporting reasoning.

A useful expenses schedule has the date, supplier, amount, description and document reference. It can also contain a question column. This separates the act of collecting evidence from deciding the tax treatment. It helps prevent both missing legitimate costs and including amounts that do not belong in the business calculation.

9. Confirm the accounting method before comparing totals

The timing of income and expenses depends on the accounting method that applies. HMRC's overview of self-employed records explains cash basis and traditional accounting, including the current default position for eligible businesses. Discuss the method with your accountant rather than changing your spreadsheet approach halfway through the year.

A supplier invoice, payment and stock delivery may occur on different dates. A customer invoice may remain unpaid at the reporting date. These are ordinary commercial situations, but the records need to show what happened. Confusion develops when an owner compares invoice totals with bank totals and assumes the difference must be an error.

If the business has changed methods or systems, keep an explanation of the transition. Identify any opening figures transferred from the old records. The accountant can then review the connection between periods. Consistency is valuable because it makes movement understandable, not because one method can be selected solely to produce a preferred result.

10. Separate property information from trading information

If you receive property income, collect the relevant rent statements, agent records and supporting expenditure documents in a separate schedule. Explain ownership arrangements, changes in occupancy and any substantial work during the year. Where a property is jointly owned, make clear whose records and income share the documents describe.

Do not assume that every property-related payment has the same tax treatment. Repairs, improvements, finance costs and personal expenditure raise different questions. A description of the work and the invoice are more helpful than a category called “property costs”. If you are unsure, retain the evidence and ask.

Keep records of amounts held or deducted by an agent, because the net payment arriving in the bank may not show the full transaction history. The aim is to explain how the statements reconcile with receipts and expenditure. This prevents a bank-only approach from overlooking information that matters to the return.

11. Check savings, dividends and other personal income

Personal income can be easy to overlook when most of the preparation effort goes into the business. Collect interest statements, dividend documents and any other relevant income information. Identify the owner of an account or investment and the period covered rather than assuming every statement belongs to the same tax year.

A useful check is to compare this year's source list with last year's, then explain additions and removals. A closed savings account, a new investment or a pension starting partway through the year may need a document even if the amount is small. Whether it affects the tax calculation is a question to assess with complete information.

For overseas matters or asset disposals, flag the facts early so the required scope can be discussed. Do not leave them as a final note after the return is nearly ready. Complex circumstances may need additional information and work beyond routine business records preparation.

12. An illustrative preparation example

Consider a sole trader who sells packaged goods to local shops and also has employment income. The bank account contains customer receipts, personal transfers and payments to overseas suppliers. Several supplier invoices arrived after the goods, and one customer has an unresolved credit note. This is a fictional example used to explain the preparation process, not a client case study.

The owner first separates employment documents from trading records. Next, they list the business bank accounts and identify transfers between them. They connect supplier invoices to payments and mark the missing freight invoice as an open question. The customer credit note is linked to the original sale so the accountant can see the reason for the adjustment.

The improvement is not a lower tax bill promised by a different spreadsheet. It is a clearer financial record with fewer unsupported assumptions. That gives the accountant a better basis for preparing the accounts and discussing the return, while the owner can see which information still needs attention.

13. Maintain a short unresolved-items list

A question list is one of the simplest ways to make preparation more efficient. Record the item, why it is unclear, the evidence available and who may be able to resolve it. For example, a supplier refund might need a credit note, or a payment description might need confirmation from the person who ordered the goods.

Keep the list short enough to use. Avoid copying every transaction into it simply because the accountant will review the records. Focus on missing information, unusual items and differences that have already been identified. When a question is resolved, note the answer and the document supporting it.

This creates a record of decisions instead of a string of disconnected emails. It is particularly useful when several people keep records for the business. The person who knows about a warehouse adjustment may be different from the person handling invoices. A shared question list connects the knowledge without assuming everyone has the same background.

14. Review the return as a financial explanation

Before submission, ask for an explanation of the relevant figures and compare them with the information supplied. Look at the income sources, business result, known changes and any estimates or adjustments needing discussion. Review is an opportunity to confirm the facts, rather than simply signing a document because its total looks plausible.

Ask how the tax calculation and payment position connect. A figure in the return, a balancing payment and a payment on account do not necessarily represent the same period or purpose. Understanding that distinction helps with cash planning. Our separate guide to payments on account explains a practical budgeting approach.

If something is missing or appears wrong, raise it before authorising submission. Keep the final version and the explanation of significant points with the preparation file. This provides a useful reference for future questions and makes next year's handover easier.

15. Use this preparation to improve the next cycle

Once the return is complete, identify the two or three record problems that caused the most effort. They might be missing supplier invoices, unclear personal spending or customer payments that were never allocated. Choose a practical change for each problem instead of attempting to redesign every system at once.

For example, ask the person placing an order to upload the invoice to a shared folder, review bank transactions monthly and record the reason for credit notes when they are issued. These are manageable routines. They reduce the need to reconstruct a year of events from memory when the next return is due.

If MTD for Income Tax is relevant to your circumstances, discuss its timetable separately. The move to digital records does not remove the need for complete information. Read our MTD entry-date guide to understand the questions to check before changing the reporting routine.

16. A practical handover checklist

• Confirm the taxpayer, tax year, reason for filing and relevant notices.
• List every income source and the documents supporting it.
• Provide complete business bank and transaction records, including other payment channels.
• Identify the accounting method and any system changes.
• Keep invoices, credit notes and expense explanations connected.
• Separate property, employment and personal income information.
• Explain unusual events, missing records and unresolved differences.
• Agree a review timetable that leaves time for questions.
• Understand the payment position and plan the cash separately from filing.
• Keep the completed return and supporting explanations together.

CRV Gudka & Co is an accounting practice in Edgware with a dedicated team supporting businesses and private clients. We can discuss Self Assessment and relevant tax work, connected bookkeeping and annual accounts. Tell us the year involved, your income sources and the condition of your records so that we can agree a useful scope. You do not need a perfect folder to start the conversation, but a clear outline helps the team identify the right next steps.