Everyone approaches the self-assessment deadline in their own way.
Some have their records organised well in advance, while others find themselves sifting through a pile of receipts at the last minute.
Wherever you are in the process, this guide will walk you through everything you need to complete your tax return accurately and on time.
We’ll cover key steps, common issues avoid, and potential tax-saving opportunities to ensure you’re fully prepared.
We’ve also included a checklist to keep beside you as you file – so you don’t make some of the common mistakes we see every year!
Initial Steps
Before you even open your tax return, you need to know exactly what HMRC expects from you.
Each person’s tax situation is different, and understanding yours is the first step to getting it right.
Many people think self-assessment is just for the self-employed. Actually, you might need to complete a return if you’re a company director, earn money from property, have significant investment income, or need to claim certain tax reliefs.
Each of these situations requires different information and has its own particular rules.
Let’s start with what you absolutely must have before you begin. Without these essentials, you won’t be able to complete your return properly:
- Your UTR (Unique Taxpayer Reference), the 10-digit number HMRC uses to identify you
- Government Gateway ID and password for online filing
- All your income records from the tax year
- Records of any expenses you plan to claim
- Bank statements covering the full tax year
If you’re missing any of these, don’t panic. Getting replacement documents or accessing online records usually takes just a few days. Tackle this now rather than leaving it until the last minute!
Understanding Your Filing Requirements
With many different steps and hundreds of boxes and fields to fill out, every self-assessment is different.
What you need to do depends entirely on how you earn money. Missing deadlines or making mistakes can lead to penalties, so understanding your exact requirements is crucial.
Self-Employed and Sole Traders
Whether you’re running a full-time business or have a side hustle, you need to register for self-assessment as soon as you start trading.
The tax year runs from 6 April to 5 April, and you must file a return for any tax year where you earned over £1,000 from self-employment.
For your return, you’ll need to:
- Total all business income – Include all payments received from clients or customers, whether by cash, bank transfer, PayPal, Stripe, or any online platform like Etsy, eBay, or Upwork.
- Calculate allowable expenses – Only claim costs that are wholly and exclusively for business, such as office supplies, software subscriptions, marketing, travel for work, and professional fees.
- Keep evidence of everything – Retain receipts, invoices, and bank statements to support your expense claims. HMRC may request proof if they review your return.
- Determine the business use of personal items – If you use personal assets for work, such as your phone, vehicle, or home, you must calculate the proportion that applies to business use. For phone bills, this means working out what percentage of calls are for work. For vehicle expenses, you can claim based on business mileage (45p per mile for the first 10,000 miles) or a percentage of actual costs like fuel and insurance. If you work from home, you can claim a portion of rent, mortgage interest, electricity, and internet based on business use.
As noted, remember to include income from all platforms – eBay, Etsy, Amazon, freelance sites.
HMRC has been known to contact those with ‘side hustles’ who fail to declare income from these sites and others.
Landlords
Property income requires careful attention in your tax return as it can complex and time-consuming to work out your income and deduct expenses. Even if you’re making a loss, you must file.
Your return needs to include:
- Total rent received from all properties
- Allowable expenses like repairs, insurance, and agent fees
- Mortgage interest payments (now restricted to 20% tax relief)
- Any periods when properties were empty
Different rules apply for short-term lets like Airbnb versus long-term rentals. If you rent out a room in your own home, check if you qualify for the Rent a Room scheme’s £7,500 tax-free allowance.
Company Directors
Being a director means filing a return regardless of how you take money from your company.
You need to report:
- All salary payments (shown on your P60)
- Every dividend taken during the tax year
- Any benefits (like private health insurance or company car)
- Director’s loan account transactions
Pay special attention to timing with dividends – they count for the tax year when they’re paid, not when they’re earned. Keep dividend vouchers for every payment.
High Earners (Over £100,000)
Once your income tops £100,000, tax gets more complicated. Your personal allowance starts reducing by £1 for every £2 you earn over this amount.
Your return must include:
- All employment income and benefits
- Investment earnings including dividends
- Rental income from properties
- Any other income sources
Mixed Income Sources
Having multiple income streams makes your return more involved. You need to report everything accurately and understand how different types of income interact.
Include:
- Employment income from all jobs
- Self-employed earnings
- Property rental income
- Investment returns
Remember that some allowances apply across all your income, while others are specific to certain types of earnings.
Allowable Expenses: Getting It Right
Claiming expenses is one of the trickiest parts of self-assessment. Many people either miss out on legitimate claims or try to claim things they shouldn’t.
Understanding what you can and can’t claim isn’t just about reducing your tax bill – it’s about accurately reporting the true costs of earning your income.
If You’re Self-Employed
Running your own business involves all sorts of costs.
The basic rule seems simple – expenses must be “wholly and exclusively” for business. But in practice, this can get complicated, especially when something has both business and personal use.
Travel expenses often cause confusion because the rules aren’t always obvious. The key is understanding the difference between regular commuting (which you can’t claim) and genuine business travel.
Allowable travel costs typically include:
- Business mileage at 45p per mile for the first 10,000 miles
- Train tickets to client meetings
- Hotel stays for business trips
- Parking fees at client sites
For Landlords
Property expenses work differently from business expenses. The main rule here is maintaining versus improving. Repairs that keep your property in good working order are allowable, but improvements that add value usually aren’t.
Many landlords miss out on legitimate expenses because they’re not sure what counts. Understanding the difference between repairs and improvements is crucial for your tax return.
Allowable property expenses include:
- Repairs that restore the property to its original state
- Letting agent fees and management costs
- Insurance premiums
- Utility bills you pay for tenants
View our blog on capital allowances for property investors here and replacing domestic items here.
Self-Assessment Tax Return Checklist
Here’s how self-assessment checklist. Feel free to use it when submitting your return or saving it for later.
| Step | What You Need | Key Details | Common Pitfalls |
|---|---|---|---|
| 1️⃣ Gather Information | UTR Number | 10-digit Unique Taxpayer Reference (UTR) from HMRC. | Can take a while to retrieve if lost – check old tax returns or HMRC letters. |
| Government Gateway Login | Needed to file online; reset if forgotten. | Waiting too long to reset can cause delays. | |
| Income Records | P60/P45 (employment), invoices (self-employment), rent statements (landlords), dividend statements (investments), savings interest. | Forgetting rental or freelance income – HMRC cross-checks bank data. | |
| Expense Records | Receipts, invoices, mileage logs, utility bills (if claiming home office use). | Claiming expenses without proof – HMRC may ask for receipts. | |
| Tax Reliefs & Allowances | Pension contributions, Gift Aid donations, Marriage Allowance, Rent-a-Room relief (£7,500 threshold). | Missing out on reliefs – these can lower your tax bill. | |
| 2️⃣ Completing Your Return | Employment Income | Enter salary (P60), taxable benefits (P11D), bonuses. | Figures must match employer records – HMRC has this data. |
| Self-Employment Income | Total earnings from all sources, including cash & digital payments. | Forgetting side earnings (Etsy, eBay, freelancing) – all taxable. | |
| Allowable Business Expenses | Office costs, travel (45p per mile), phone bills (business portion), software, advertising. | Claiming personal expenses – only work-related costs are deductible. | |
| Property Income | Total rent received, allowable expenses (repairs, agent fees, mortgage interest at 20% relief). | Misclassifying improvements as repairs – only maintenance is deductible. | |
| Investment Income | Dividends (gross amount), savings interest, capital gains. | Forgetting to declare taxable investment gains. | |
| 3️⃣ Review Before Submission | Compare to last year’s return | Look for inconsistencies – HMRC flags sudden income changes. | Large drops in reported income can trigger an audit. |
| Double-check figures | Ensure numbers match payslips, bank statements, and receipts. | Rounding errors – HMRC expects precise amounts. | |
| Check expenses are reasonable | Avoid excessive claims that may raise red flags. | Overclaiming – HMRC rejects unreasonable expenses. | |
| Review tax code | Check for incorrect codes that might mean under/overpaying tax. | Wrong tax code = unexpected tax bill. | |
| Confirm ‘payment on account’ requirement | If tax due is over £1,000, you may need to prepay next year’s tax. | Ignoring this means you owe two years’ tax in one go. | |
| Save a copy of your return | Download a PDF or print for records. | It’s just good practice! | |
| 4️⃣ Deadlines & Penalties | 5 October: Register for self-assessment | Must register if first-time filer. | Late registration can lead to fines. |
| 31 October: Paper return deadline | Postal submission cut-off. | £100 fine for missing it. | |
| 31 January: Online submission & payment due | Final deadline for filing and tax payment. | Late filing = £100 fine; unpaid tax = interest charges. | |
| 31 July: Payment on account due (if applicable) | Second advance tax payment. | Ignoring this leads to interest & fines. | |
| 5️⃣ Paying Your Tax | Payment Methods | Direct Debit, online banking, debit/credit card, cheque. | Bank transfers can take several days – pay early. |
| Tax Reduction Strategies | Claim all eligible reliefs, maximise pension contributions, ensure correct tax code. | Missing reliefs = paying more tax than necessary. | |
| Set up a payment plan if needed | Use HMRC’s Time to Pay if struggling with payments. | Ignoring tax debt leads to penalties & possible legal action. |
Let Us Handle Your Self-Assessment
Getting your tax return right takes time and expertise. Whether you’re self-employed, a landlord, company director, or have multiple income sources, the Double Point team knows exactly what you need to do.
We make sure you’re claiming everything you’re entitled to while staying fully compliant with HMRC rules. Our expertise means you won’t miss deadlines, overlook claims, or make costly mistakes.
Our self-assessment service includes:
- Full return preparation and submission
- Expense review and optimisation
- Tax planning advice
- Dealing with HMRC on your behalf
- Year-round support
Don’t leave your tax return to chance. Contact Double Point today and let us take the stress out of self-assessment.
