You Have Registered for Self Assessment. Now What? A Step-by-Step Guide for Online Sellers

You have registered for Self Assessment. The 5 October deadline has passed, your application is in, and your Unique Taxpayer Reference is on its way. Now the question is: what do you actually do next? This guide walks you through every step, from finding your income figure to understanding what you will owe in January, written specifically for online sellers on Vinted, eBay, Depop , Amazon and Etsy who are filing for the first time.

Jade has been selling pre-loved clothing on Vinted and eBay since early 2025. By the end of the 2025/26 tax year she had received £6,400 from sales across both platforms. She registered on time. What she did not have was any record of her expenses, any idea of how to calculate her tax, or any understanding of what the January deadline would actually ask of her. This guide covers everything she needed to know, and everything you need too.

Not Sure Whether You Even Need to Register?

Before we get into what happens after registration, it is worth a quick check.

If you sell on Vinted, eBay or Depop and you have earned more than £1,000 from selling in the 2025/26 tax year (6 April 2025 to 5 April 2026), you need to register for Self Assessment. The £1,000 refers to your total income from selling, not your profit after costs.

The registration deadline for the 2025/26 tax year was 5 October 2026. That date has now passed.

If you have not yet registered, register now. A late registration is far better than no registration. HMRC's penalty system is designed around unpaid tax, not around a few weeks' delay. If your profits were below the £12,570 personal allowance, the risk of a penalty for late registration is low. But do not wait any longer.

You can register at gov.uk

The 5 October deadline is covered in detail in our article Do You Need to Register for Self Assessment? The 5 October Deadline Explained.

The Six Steps After Registration

Step 1: Wait for Your UTR

Your Unique Taxpayer Reference is a 10-digit number that HMRC sends to your registered address by post. It takes up to ten working days to arrive.

You cannot file your tax return without it. You cannot activate your online Self Assessment account without it. Until it arrives, there is nothing you can do on the HMRC side.

What you can do while you wait: reconstruct your income and expenses. That is exactly what Steps 2, 3 and 4 are for. Use the waiting time productively.

When your UTR arrives, store it somewhere you will find it again. You will need it every January for as long as you remain self-assessed.

Step 2: Find Your Total Income

Your tax return asks for your total income from selling. That means every sale, across every platform, for the full tax year from 6 April 2025 to 5 April 2026.

Where to find it:

Most selling platforms provide a summary of your activity. Log in to each platform you used and look for a sales report, earnings summary or transaction history.

• Vinted: go to your profile, then My Sales. Export or screenshot your completed sales.

• eBay: go to Seller Hub, then Reports. Download a transaction report for the relevant dates.

• Depop: go to your profile, then Sold items. Your earnings are shown per item.

What to include:

Include the price the buyer paid for the item itself. Delivery charges that the buyer paid should also be included unless they passed directly through the platform and never touched your account (this is standard for Vinted's integrated postage). If you are unsure, include it and note the amount.

What not to include:

Platform fees, PayPal fees and postage costs you paid come off as expenses. They are not subtracted from income at this stage.

Do not overlook smaller platforms. If you also sold on Facebook Marketplace, Etsy or any other platform, those sales count too.

Step 3: Reconstruct Your Expenses

Expenses reduce your taxable profit. Most online sellers underestimate them because they have not tracked them throughout the year. If this is you, now is the time to piece them together.

Go through your bank statements and email inbox for the full tax year. You are looking for:

• Stock costs : everything you paid to acquire the items you sold for resale. Keep this separate from items you originally bought for personal use.

• Postage and packaging : any postage you paid to send items, and any packaging materials you bought.

• Platform fees : selling fees charged by eBay, Depop or other platforms. Vinted does not charge seller fees.

• PayPal or payment processing fees : charges taken before money reached your account.

• Mileage : if you drove to collect stock, drop off at a post office or attend a market, you can claim 45p per mile for the 2025/26 tax year. Keep a note of each trip: date, reason, start point and destination.

• Home office : a proportion of your broadband or phone costs if you used them for the business.

• Photography equipment : if you bought props, a lightbox, a camera or similar items used to photograph stock.

• Subscriptions : any apps, tools or software used for the business.

If you do not have receipts for everything, a reasonable estimate with a clear basis is better than leaving it out. Write down how you arrived at the figure.

You can find a fuller list of commonly missed expenses in our article Sole Trader Expenses That Are Commonly Missed on a Tax Return.

Step 4: Enter Everything Into a Bookkeeping Record

This is where your numbers go from scattered notes into a structured record. A clear bookkeeping record does three things:

• it tells you your profit,

• it tells you your tax estimate, and

• it gives you something accurate to enter on your return.

The 2025/26 Sole Trader Template is built for exactly this situation. It is a structured spreadsheet designed for online sellers and sole traders who are entering their numbers for the first time.

What the template includes:

• An income log where you enter each sale by date, platform and amount

• An expenses section with labelled categories so nothing is missed

• A mileage tracker for business journeys

• A tax summary that calculates your taxable profit, income tax, National Insurance and estimated January payment

• A set-aside dashboard that tells you what % of each sale to save going forward

You do not need accounting software. If you are a sole trader with straightforward income from a small number of platforms, the template handles everything a first-time Self Assessment filer needs.

If you have no records at all and are starting from scratch, read our article No Records for Self Assessment 2025/26? Here Is What to Do before entering anything.

Step 5: Understand What You Will Owe in January

Your Self Assessment payment is due on 31 January 2027. That is the tax you owe for the 2025/26 tax year.

What surprises many first-time filers is that the January bill may be larger than expected. Here is why.

If your tax bill is over £1,000, HMRC will also ask for a Payment on Account at the same time. This is an advance payment toward your 2026/27 tax bill. It is calculated as 50% of your current bill and is due on the same day.

So if your tax for 2025/26 is £1,800, your January total will be:

• Tax for 2025/26: £1,800

• First Payment on Account for 2026/27: £900

• Total due 31 January 2027: £2,700

A second Payment on Account of £900 is then due on 31 July 2027.

This is not a penalty. It is simply the system running ahead of itself. But it catches first-time filers completely off guard every year.

Payment on Account is explained in full in our article Payment on Account: What It Is and How to Avoid the January Shock.

If you also have PAYE income from an employer alongside your self-employment income, the calculation is different. Some of your tax may already have been collected through your pay. Read PAYE and Self-Employed in the Same Tax Year: How Self Assessment Works for a clear explanation.

The 2025/26 Sole Trader Template calculates your estimated January total, including Payment on Account where applicable, so you are not caught out.

Step 6: File Your Return

The deadline for filing your Self Assessment return online is 31 January 2027. Paper returns have an earlier deadline of 31 October 2026, which for most online sellers has already passed, so you will be filing online.

What the return asks for:

• Your total income from self-employment (the gross figure before expenses)

• Your total allowable expenses

• Any other income sources (employment, savings interest, rental income)

• Any student loan repayments that apply

The return calculates your tax bill from the numbers you enter. It is a data entry exercise. If you have followed Steps 2 to 5 and have your income and expenses organised, the filing itself is straightforward.

File early. Filing in November or December rather than January means you know your bill with time to plan the payment, rather than finding out what you owe two weeks before it is due.

A Real-World Example: Jade Morrison

Jade sells pre-loved clothing on Vinted and eBay. She registered for Self Assessment in October 2026, her first year filing.

She had not kept records during the year. Working through her Vinted earnings page and eBay Seller Hub, she found she had received £6,400 across both platforms. Her PayPal statements showed £340 in fees. She had spent approximately £1,100 buying stock. She also recalled driving to collect a large batch of items twice, approximately 40 miles in total.

Her mileage deduction: 40 miles at 45p = £18.

She entered everything into the 2025/26 Sole Trader Template:

• Total income: £6,400

• Expenses: £1,458 (stock £1,100, fees £340, mileage £18)

• Taxable profit: £4,942

• Income tax: £0 (below the £12,570 personal allowance)

• National Insurance: £0 (below the £12,570 lower profits limit)

• Total due in January: £0

Jade had nothing to pay. But she had done it correctly, her records were in order, and she filed on time. She also learned what to track in 2026/27 so she does not have to reconstruct it again.

FAQ

What is a UTR and when will I get it?

A UTR is a 10-digit number HMRC uses to identify you for tax. It arrives by post within ten working days of registration. You cannot file without it, so use the waiting time to reconstruct your income and expenses.

I have no records at all. Can I still file?

Yes. Platform earnings pages (Vinted, eBay, Depop) all provide downloadable summaries. Bank statements fill in the expenses. A reasonable reconstruction based on available evidence is acceptable and far better than not filing. Read No Records for Self Assessment 2025/26? Here Is What to Do for a step-by-step approach.

What is the filing deadline?

Online returns for the 2025/26 tax year must be submitted by 31 January 2027.

What is Payment on Account?

If your tax bill for 2025/26 exceeds £1,000, HMRC adds a 50% advance payment toward next year's bill on top of what you owe. This is due on the same date, 31 January 2027. It is not a penalty. Full details are in our article Payment on Account: What It Is and How to Avoid the January Shock.

Do I include Vinted delivery income in my sales total?

In most cases, no. When a buyer pays for postage through Vinted's integrated labels, the money passes directly through Vinted and does not come to you. Your income is the item sale price only. If you arranged your own delivery and the buyer paid you separately, include that amount.

Can I use the Trading Allowance instead of claiming expenses?

Yes. A flat £1,000 Trading Allowance can be deducted from gross income instead of itemising actual expenses. It is only the better option if your real expenses total less than £1,000. If you spent more than that on stock, postage, fees and packaging, claiming actual expenses saves you more tax.

The 2026/27 Tax Year Has Already Started

While you are working on your 2025/26 return, the 2026/27 tax year is already underway. Every sale you make from 6 April 2026 onwards is 2026/27 income.

The biggest difference between this year and last year can be a proper record from day one. A bookkeeping template that runs throughout the year means you will not be reconstructing anything next October.

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