E-commerce Accounting, Inventory Costing & Multi-Channel Sales Tax (VAT)

The real cost of selling online in the UK and how to account for every penny

From warehouses in Wolverhampton to drop-ship suppliers in Shenzhen, British online sellers are navigating a compliance landscape that shifts faster than a flash sale. Here’s what your books actually need to reflect.

In this guide

Inventory costing: FIFO, AVCO & the landed cost trapVAT in 2025: thresholds, marketplaces & post-Brexit rulesMaking Tax Digital: what’s mandatory right nowTech stack every UK seller needsFrom reactive to strategic

Inventory costing: where your margin lives or dies

Ask any e-commerce founder what their gross margin is, and most will quote a number from their Shopify dashboard. The problem? That number is only as accurate as the cost values sitting beneath it — and cost accounting is where most UK sellers quietly lose thousands without realising.

Two methods HMRC actually accepts

Option 1

FIFO

First-In, First-Out. The oldest stock is assumed to be sold first. During periods of supplier price inflation, this yields a higher closing inventory value and a higher reported profit. Common with fashion and perishables.

Option 2

AVCO

Average Cost. Recalculates a weighted mean every time stock arrives. Irons out the currency-driven price swings that affect UK sellers importing from Asia. Favoured by high-volume, multi-SKU operations.

HMRC reminder

LIFO (Last-In, First-Out) is not permitted under UK GAAP or HMRC guidelines. Using it even inadvertently through older accounting templates can misstate your Corporation Tax liability. If you’ve inherited a spreadsheet system, check this first.

E-commerce Accounting, Inventory Costing & Multi-Channel Sales Tax (VAT)

The landed cost trap — and how to escape it

Recording only the factory gate price is the single most common costing error in UK e-commerce. Your true cost of goods includes everything required to get that unit from the supplier’s floor to your fulfilment centre. Miss any component, and your margin calculations are fiction.

• International freight and sea or air shipping fees
• UK Customs duties and HMRC import declarations
• Cargo insurance during transit
• Sourcing agent or freight forwarder commissions
• Port handling and last-mile delivery to your warehouse

Practical tip

Build landed cost as a percentage multiplier per supplier and update it quarterly. A supplier in Guangzhou whose freight rates jumped 40% in a single quarter can quietly destroy a margin that looked healthy on paper six months ago.

VAT in 2025: more moving parts than ever

Selling across Shopify, Amazon UK, and eBay doesn’t just triple your admin it exposes you to three overlapping VAT frameworks simultaneously. Understanding which rules apply to your specific business structure is non-negotiable.

Current thresholds at a glance

Mandatory VAT registration threshold£90,000

Deregistration threshold£88,000

Threshold unchanged since April 2024

Standard VAT rate20%

Late payment penalty (15 days)2% of the unpaid

Watch this

HMRC measures turnover on a rolling 12-month basis, not tax year. A strong Q4 can silently push you over the threshold before you’ve noticed. Accountants recommend monitoring your position when you cross 75% of the limit (around £67,500).

Marketplace facilitator rules don’t assume Amazon handles it

Since January 2021, platforms like Amazon and eBay have taken on VAT collection responsibility for many overseas sellers. As a UK-based business, however, you retain primary compliance responsibility. In 2025, HMRC receives sales data directly from these platforms and automatically cross-references it against your VAT returns. Discrepancies trigger enquiries, not letters requesting clarification, but formal compliance checks.

Postponed VAT Accounting (PVA) remains one of the most underused tools available to UK importers. Rather than paying import VAT at the border and waiting to reclaim it on the next return, PVA lets you account for it on the same return, significantly improving cash flow for businesses holding large stock positions.

Post-Brexit EU sales: OSS and IOSS explained plainly

Selling goods into the EU from the UK now requires navigating two separate schemes depending on consignment value.

The Import One-Stop Shop (IOSS) applies to parcels valued below €150. Registering for IOSS means you collect EU VAT at checkout — your customer pays nothing at the door, and the parcel clears customs cleanly. Skip IOSS and your European buyers face unexpected border charges on delivery: a reliable way to tank your Trustpilot score and inflate your return rate simultaneously.

The One-Stop Shop (OSS) covers ongoing digital service sales to EU consumers, allowing you to file a single return rather than registering in each member state individually.

Making Tax Digital: where things stand right now

The UK’s MTD rollout is ongoing — and the deadlines keep moving closer. Here’s the current state of play, without the jargon.

MTD for VAT is already fully mandatory. Every VAT-registered business, regardless of turnover, must keep digital records and submit returns through HMRC-recognised software. Manual entry, even via a spreadsheet without a digital link, is a compliance failure. HMRC has tightened penalties under the points-based system introduced in 2025, and late payment now attracts structured charges from day 15.

MTD for Income Tax (MTD ITSA) arrives in April 2026 for sole traders and landlords earning above £50,000, extending to the £30,000 bracket from April 2027. Instead of one annual Self Assessment, quarterly income-and-expense updates become mandatory — which means year-round accuracy rather than a January scramble.

Key update — 2026

HMRC confirmed in its July 2025 Transformation Roadmap that MTD for Corporation Tax is not currently planned. E-commerce limited companies are not in scope for MTD ITSA, but all VAT obligations remain fully live.

The tech stack that keeps you compliant

Good accounting software doesn’t replace an accountant, but the wrong software guarantees your accountant more problems to fix. These are the categories worth investing in.

Inventory

Linnworks, Veeqo, and Cin7 sync stock across channels, flag low margin SKUs

Cloud accounting

Xero, QuickBooks, and Sage are all MTD-compatible and integrate with HMRC’s API

Tax engines

Avalara and TaxJar automate VAT rate calculation across the UK, EU and beyond

The non-negotiable requirement is that every software component in your chain connects via a digital link. Once data enters your accounting system, it cannot be manually transferred to another system, which breaks the MTD digital chain and creates a compliance gap.

From reactive to strategic

Year-end accounting panics are a symptom, not a problem. The underlying issue is usually that financial data is treated as a record of what happened rather than a signal for what to do next. Landed cost accuracy, VAT reconciliation, and digital record-keeping are not administrative luxuries they are the infrastructure on which every scaling decision rests.

If you can’t tell, in real time, what your margin is after VAT, import duty, and fulfilment costs, you’re not pricing, you’re guessing. And in a market where your competitors are a Google tab away, guessing is expensive.

For any help, the SKZ Accountant is available to you. From every different location, like Accountants in Barking, Accountants in Central London, Accountants in Croydon, Accountants in Stratford, Accountants in Middlesbrough, Accountants in Canary Wharf, Accountants in Brentwood, Accountants in Romford, Accountants in Newham, Accountants in Ilford, contact him anywhere in the UK