If you are hiring an Online Personal Tax Accountant for the first time, the main question is usually what to send and in what form. Most delays I see in practice come from missing paperwork rather than complicated tax, and a clean set of documents can save you weeks and fees.

An Online Personal Tax Accountant works entirely from the records you upload, so the quality of those records decides the quality of your return. The figures below relate to the 2025/26 tax year, which most people will be reporting before the 31 January 2027 online filing deadline.

Proof of identity and HMRC authorisation

Your accountant needs to confirm who you are before acting for you. Send a passport or driving licence, your Unique Taxpayer Reference (UTR), and your National Insurance number.

They will also ask you to authorise them through HMRC's online agent services, using form 64-8 or the digital equivalent. Without this, they cannot see your tax account or speak to HMRC on your behalf.

Employment income paperwork

If you were employed, the essentials are:

• Your P60 for the year, showing total pay, tax deducted and National Insurance.

• Any P45 from a job you left, which records pay and tax up to your leaving date.

• A P11D if your employer provided benefits such as a company car or private medical cover.

• Payslips, if you cannot find the P60 or you changed jobs mid-year.

A common scenario: a client leaves one job in September and starts another in October, then discovers an emergency tax code has been applied. The P45 and the new payslips show whether too much tax was taken.

Self-employment records

Sole traders should send a full year of income and expenses. That means sales invoices, bank statements for the business account, receipts for costs, mileage logs, and a note of any use of home as office.

If your gross trading income is £1,000 or less, the trading allowance may mean you do not need to report it at all. Above that level, you can either deduct the £1,000 allowance or claim your actual expenses, whichever is better.

Rental income documents

Landlords need to supply rent statements from letting agents, mortgage interest certificates, repair invoices, insurance, service charges and ground rent. Capital improvements should be kept separate from repairs, because only repairs are deductible against rent.

Remember that for residential lettings, mortgage interest is not deducted as an expense. Instead you receive a basic-rate (20%) tax credit. For example, rent of £14,000, allowable costs of £4,200 and mortgage interest of £5,000 gives taxable profit of £9,800, with a £1,000 credit against the tax due.

Savings, dividends and investment income

Send your bank and building society interest certificates, dividend vouchers, and platform annual tax summaries. The Personal Savings Allowance is £1,000 for basic-rate taxpayers and £500 for higher-rate taxpayers. The dividend allowance is £500.

Quick reference by taxpayer type

Which Documents Can Reduce or Change Your Bill?

Basic income evidence gets the return filed. The papers in this section are what stop you overpaying.

Pension contributions and Gift Aid

Send contribution statements for personal pensions and SIPPs. Where you pay into a relief-at-source scheme, the provider claims 20% basic-rate relief, but higher and additional-rate taxpayers claim the extra 20% or 25% through their return. Gift Aid donations extend your basic-rate band in the same way, so keep your donation records.

Capital gains paperwork

Disposals of shares, second homes or buy-to-let property need purchase and sale contracts, completion statements, and receipts for enhancement costs and legal fees. The annual exempt amount is £3,000, with gains above it taxed at 18% or 24% depending on your income band.

Residential property gains must be reported to HMRC within 60 days of completion, so tell your accountant straight away rather than at year-end.

Child Benefit and student loan details

Bring your Child Benefit award notice if your income exceeds £60,000, since the High Income Child Benefit Charge applies and tapers fully at £80,000. Also provide Student Loan plan type and any statements, because repayments are calculated through self-assessment for many taxpayers.

Marriage Allowance and other claims

Married couples or civil partners where one earns under the £12,570 personal allowance may transfer £1,260 of allowance. Include both partners' details and National Insurance numbers. If you work from home or buy tools or uniforms, send evidence for those expense claims as well.

Last year's return and payments on account

Your accountant needs the prior-year tax calculation (SA302) and a statement of account showing payments on account. Payments are due on 31 January and 31 July, each normally half of the previous year's liability. A client whose income has dropped can apply to reduce them, but only with the right figures to hand.

Records for Making Tax Digital

Making Tax Digital for Income Tax began on 6 April 2026 for sole traders and landlords with qualifying income above £50,000, extending to £30,000 from April 2027 and £20,000 from April 2028. If it applies to you, your accountant will need digital records and quarterly updates, not just a year-end bundle.

How to Send Your Paperwork Securely and Efficiently

Prepare everything before you upload

Scan documents clearly and name each file sensibly, such as "Rental-Statement-2025-26". Group files by income type. A tidy folder lets your accountant start work immediately instead of sending you requests.

Protect your personal data

Never email passports, UTRs or bank details in plain attachments. Use the encrypted client portal that a reputable firm provides, and check that the firm is registered with HMRC for anti-money laundering supervision and holds professional indemnity insurance.

Mind the deadlines

Register for self-assessment by 5 October following the tax year if you are new to it. Paper returns were due on 31 October 2026, while online returns and tax payment are due by 31 January 2027. Ask for a firm internal deadline: I normally request documents by mid-December so there is time to query anything.

Avoid the penalties

Missing the filing deadline costs an automatic £100, then £10 per day after three months up to £900, then further charges of the greater of £300 or 5% of the tax due at six and twelve months. Interest also runs on late tax, and these penalties apply even if you owe nothing.

Common mistakes I see

Clients often forget a small savings account, omit a P45 from a short-lived job, or treat a Child Benefit claim as irrelevant because their partner earns more. Another frequent error is combining personal and business spending on one account, which makes the records far harder to verify.

Final thoughts

The right documents turn your return from an anxious chore into a routine task. Gather your identity details, income evidence and claim records early, and send them securely to your Online Personal Tax Accountant well ahead of 31 January. Preparation is the cheapest tax saving available.