UK businesses expanding to the US: When sales tax becomes mandatory (not optional)

For many growing U.K. ecommerce businesses, the U.S. is the natural next step. It offers scale, high consumer spending, and seamless access through platforms like Shopify and Amazon, and U.S.-based fulfilment networks. But what businesses routinely experience is just how quickly U.S. sales tax exposure builds and just how complex it can become.

Unlike U.K. value added tax (VAT), U.S. sales tax is governed at state level. There’s no single national (federal) system. Each state sets its own thresholds, rates, filing frequencies, and enforcement rules. Once your activity crosses certain thresholds, registration and compliance are mandatory — not optional.

At the same time, the import landscape has tightened. As of 29 August 2025, the long-standing U.S. de minimis exemption — which allowed many shipments under $800 to enter duty-free — effectively ended for most imports. Goods entering the U.S. are now generally subject to duty, with flat tariff rates applying in many cases. This directly affects landed cost, pricing, and margin planning.

If you’re selling into the U.S. from the U.K. — or planning to — understanding when U.S. sales tax compliance becomes mandatory is essential.

Key takeaways

• U.S. sales tax becomes mandatory once nexus is created. Economic thresholds, inventory stored in U.S. warehouses, or marketplace activity can trigger registration requirements at state level.

• U.S. sales tax and import duties are separate but equally important. Since the changes to de minimis rules, most goods entering the U.S. are subject to duty. Sales tax applies to the sale; customs duty applies to the import.

• Compliance obligations are state-specific and operational. Once triggered, businesses must register, calculate the correct tax, file returns, and remit tax.

• Scalable growth requires scalable compliance. Monitoring thresholds, integrating real-time tax calculation, adjusting pricing for tariffs, and building a structured U.S. compliance framework are essential for sustainable expansion.

Why do U.K. businesses sell to the U.S.?

For U.K. brands, the U.S. represents scale that the domestic market cannot match. A population of more than 330 million, high disposable income, and a mature ecommerce culture make it a natural target for ambitious growth plans.

Revenue diversification beyond the U.K.

For growth-focused U.K. businesses, U.S. expansion is often about resilience as much as revenue. Earning in U.S. dollars reduces exposure to domestic economic cycles and currency volatility. A broader geographic footprint can stabilise performance during slower U.K. trading periods and smooth cash flow across seasons.

U.S. revenue also strengthens strategic positioning. Investors and acquirers often view geographic diversification as a sign of maturity and scalability. A meaningful U.S. presence can increase perceived brand value and reduce concentration risk.

For many midmarket brands, expanding into the U.S. is not just incremental growth — it is a step towards becoming a global business.

U.S. market scale and opportunity

The U.S. is one of the largest consumer markets in the world, and its ecommerce channel alone is measured in the hundreds of billions of dollars per quarter. In Q3 2025, the U.S. Census Bureau estimated U.S. retail ecommerce sales at $310.3 billion, representing 16.4% of total retail sales.

That scale matters because it changes the economics of growth. Even niche U.K. brands can find meaningful volume faster than they expect — especially in categories where U.S. consumers already buy online and are comfortable purchasing cross-border.

For market selection and risk checks, U.K. exporters can also use U.S. government market research. The International Trade Administration’s Country Commercial Guides compile on-the-ground detail about market conditions, regulations, and business customs, which helps businesses evaluate demand, compliance expectations, and routes to market.

Ecommerce platforms drive early expansion

Expansion into the U.S. rarely begins with a subsidiary or office. It usually starts online.

Marketplaces like Amazon and Etsy provide instant access to U.S. buyers. Shopify and other platforms allow businesses to enable U.S. shipping with minimal setup. U.S.-based third-party logistics suppliers (3PLs) handle fulfilment and delivery expectations.

What legally changes when you start selling to the U.S.?

When a U.K. business begins selling to the U.S., the legal environment shifts immediately — even if nothing changes operationally on the surface.

In the U.S., sales tax is administered at state level, with additional local layers in many jurisdictions. Rules differ by state. Thresholds, enforcement, and filing frequencies differ.

At the same time, import duties apply at federal level. This creates a dual exposure: state-level sales tax and federal-level customs duties. For U.K. businesses, this means compliance is no longer centralised. It becomes fragmented and activity-driven.

U.S. sales tax is state based (not federal)

Sales tax in the U.S. is governed by individual states. Forty-five states impose a statewide sales tax, and many allow local counties or cities to add their own rates. Each state determines when a business must register, what products are taxable, what rate applies, and how often returns must be filed.

This is fundamentally different from VAT. Being VAT compliant in the U.K. does not translate to U.S. sales tax compliance. The systems operate on different legal foundations, with different triggers and documentation standards.

Import tariffs and duty after 2025

As of 29 August 2025, the U.S. de minimis exemption effectively ended for most imports. Most goods entering the U.S. are now subject to customs duties. In many categories, flat tariff rates apply. This directly affects landed cost and margin modelling.

Before 29 August 2025

• Shipments under $800 often entered duty-free

• Many ecommerce parcels avoided customs charges

After 29 August 2025

• Duty applies regardless of shipment value

• Import cost becomes part of pricing strategy

Sales tax and customs duty are separate obligations. One applies to the sale. The other applies to the import. Both affect profitability.

Evolving trade policy and bilateral agreements

The U.K.–U.S. trade environment continues to evolve through negotiations, tariff adjustments, and sector-specific agreements. Certain industries may benefit from quotas or revised rates over time.

However, these developments do not change the fundamentals of sales tax. State-level tax obligations are separate from federal trade policy. A favourable tariff outcome does not remove the requirement to register and collect sales tax where nexus exists.

When does U.S. sales tax become mandatory?

U.S. sales tax becomes mandatory when your business creates “nexus” in a state. Nexus is a sufficient commercial connection to trigger a legal obligation to register, collect, and remit sales tax. For U.K. businesses selling to the U.S., nexus is most commonly created in three ways:

• Economic activity exceeds a state threshold

• Inventory or physical presence exists in the state

• Marketplace rules shift collection responsibilities

These triggers are not optional tests. Once crossed, registration is required. Delaying action increases exposure, particularly because many states apply rules retroactively from the date the threshold was exceeded.

Economic nexus explained

Most states impose economic nexus thresholds based on revenue, transaction count, or both. Common examples include:

• $100,000 in annual sales into the state

• 200 separate transactions in a year

Some states measure this over a rolling 12-month period. Others use the prior calendar year. The calculation method varies. Because thresholds apply per state, a U.K. business may be compliant in 40 states and over the line in 10.

Physical presence and inventory triggers

Physical presence creates immediate nexus, regardless of revenue. This includes:

• Inventory stored in a U.S. warehouse

• Amazon FBA stock held in multiple states

• Employees, contractors, or offices in the U.S.

Many U.K. sellers create nexus unintentionally through fulfilment arrangements. Amazon may redistribute inventory across several states without direct oversight. Each location can trigger registration obligations.

Revenue size does not override physical presence. Even modest sales volumes can require compliance once inventory is in-state.

Marketplace facilitator laws

Most states now require marketplaces such as Amazon and Etsy to collect and remit sales tax on behalf of sellers. This reduces collection responsibility for marketplace transactions. However, it does not automatically eliminate all obligations.

If a U.K. business also sells through its own website, those direct sales may still require registration and filing. In some states, registration is required even if the marketplace collects all tax. Marketplace collection simplifies part of the process. It does not remove nexus.

What obligations follow once sales tax is mandatory?

Once nexus is triggered, compliance moves from monitoring to action. A U.K. business must register in each applicable state, begin collecting the correct sales tax, file returns on time, remit collected tax to the state, and maintain required documentation. This is not a single U.S.-wide process. It happens state by state.

Failure to register when required can lead to backdated assessments, penalties, and interest.

Registration and filing requirements

Registration is generally required before collecting sales tax. Once registered, the state assigns a filing frequency. This may be:

• Monthly

• Quarterly

• Annually

The frequency usually depends on projected sales volume. Even if no tax is collected in a filing period, many states still require a “zero return”. Missing filings can trigger penalties, estimated assessments, or account suspension.

Because obligations are state-specific, a business operating in multiple states may face different filing deadlines throughout the year.

Product taxability mapping

VAT treatment in the U.K. is relatively consistent. In the U.S., product taxability varies by state. For example, clothing may be fully taxable in one state and partially exempt in another. Food and supplements can have reduced or zero rates. Digital goods are also treated differently across states and counties.

The Federation of Tax Administrators and the Tax Foundation both publish state-by-state data illustrating how varied rates and tax bases can be.

U.K. brands selling hybrid products — physical goods bundled with digital services, subscriptions, or warranties — often encounter misclassification. Accurate taxability mapping is essential. Charging too little creates liability, while charging too much damages customer trust.

What operational adjustments U.K. businesses should make now

Crossing a sales tax threshold is a legal event. Managing it properly is an operational one. Many U.K. businesses treat U.S. tax as an accounting issue. In reality, it affects systems, checkout flows, fulfilment strategy, reporting processes, and pricing.

Waiting until a threshold is exceeded often results in reactive fixes. The stronger approach is to build infrastructure early — before compliance becomes urgent.

State-level revenue and threshold monitoring

U.S. sales tax exposure develops at state level. Monitoring must happen at state level too. This requires:

• Tracking revenue by destination state

• Monitoring transaction counts

• Reviewing rolling 12-month performance where required

• Accounting for marketplace and direct-channel sales separately

Manual spreadsheet tracking rarely scales beyond a few states. As revenue grows, automated threshold monitoring becomes essential. Without visibility, thresholds are often crossed quietly — and discovered later.

Tax engineering and checkout integration

Once registered for U.S. sales tax, it must be calculated correctly at the point of sale. Thousands of rate combinations exist, and product taxability rules also vary. Relying on static rate tables or manual processes therefore creates risk.

U.K. businesses selling into the U.S. typically integrate a tax calculation engine directly into Shopify, WooCommerce, and other platforms to ensure the correct rate and taxability treatment are applied in real time at checkout.

Inventory and fulfilment changes

Using U.S.-based fulfilment can simplify delivery but complicate tax. Storing inventory in a U.S. warehouse generally creates immediate nexus in that state. With Amazon FBA, inventory may be redistributed across multiple states without direct control.

This means that nexus may exist before significant revenue is generated, registration may be required earlier than expected, and compliance exposure can expand as inventory locations change. Inventory placement should be reviewed as part of tax planning — not just logistics optimisation.

Pricing and customer communication under new tariffs

With most shipments entering the U.S. now subject to duty, costs must be absorbed or passed through. Operational adjustments may include revising pricing models, showing landed cost at checkout, clarifying who pays import duties, and renegotiating supplier or fulfilment terms.

U.S. sales tax and import duty affect different parts of the transaction — but both influence customer experience and profitability. Ignoring either distorts margin forecasting.

How to measure and forecast U.S. tax and duty impact

U.S. sales tax and import duty affect cash flow differently. Sales tax is collected from customers and remitted to states. Import duty is a direct cost of bringing goods into the U.S. Both influence pricing, margin, and working capital. Without forecasting, profitable revenue can quietly erode.

Building a tax impact model

A structured model helps quantify exposure before it becomes urgent. It should:

• Estimate taxable sales by state based on current and projected revenue

• Map state and local tax rates that apply to your products

• Identify economic nexus thresholds and timing of likely registration

• Forecast duty costs using Harmonised System (HS) codes and current tariff schedules

• Include compliance costs such as registrations, filings, and system integration

This model should be updated quarterly. Thresholds may be crossed faster than expected, particularly during seasonal spikes.

Pricing and landed cost strategy

U.S. customers increasingly expect price transparency. A landed cost approach combines product price, shipping, import duty, and applicable sales tax. Showing the full cost at checkout reduces delivery disputes and unexpected customs charges.

From a strategy perspective, businesses must decide whether to absorb the duty to remain competitive, pass costs on to customers, or adjust product mix towards higher-margin lines.

How can U.K. businesses build a scalable U.S. tax and compliance strategy?

U.S. sales tax compliance shouldn’t be treated as a one-off registration project. As revenue grows, U.S. state exposure expands, filing frequency increases, and audit risk rises. The difference between manageable compliance and operational strain is infrastructure.

A scalable approach combines monitoring, automation, and governance.

Proactive monitoring and early warning systems

U.K. businesses should do everything possible to avoid a situation where U.S. sales tax thresholds are discovered after they are crossed. Scalable businesses implement:

• Automated nexus tracking by state

• Alerts when revenue approaches economic thresholds

• Consolidated reporting across marketplaces and direct channels

• Inventory-location monitoring where U.S. warehouses are used

This can serve to reduce reactive registration and limits historical exposure. Monitoring should be continuous to account for the constant changes in thresholds and evolving marketplace rules.

Centralised compliance infrastructure

Fragmented systems can create fragmented compliance. A scalable framework requires a single source of truth for U.S. sales tax rates and product taxability, integrated checkout calculation, consolidated state reporting, and central management of exemption certificates.

Governance, controls, and accountability

As U.S. revenue becomes material, governance must mature. Best practice includes:

• Clear internal ownership of U.S. tax compliance

• Defined processes for monitoring nexus

• Periodic internal reviews of filings and registrations

• Documentation retention policies for audit defence

External advisors may support strategy, but accountability remains internal. The objective is not just compliance, but to operate with confidence — knowing expansion will not create hidden liabilities.

When to use a dedicated compliance platform

Manual processes and spreadsheets may work when you’re operating in one or two U.S. states and at low volume. But they’re unlikely to be sufficient if your business is doing any of the following:

• Approaching nexus thresholds in multiple states

• Selling through both marketplaces and your own website

• Storing inventory in U.S. warehouses or using Amazon FBA

• Managing changing tariff costs

• Preparing for investment, due diligence, or acquisition

U.S. sales tax is dynamic — rates frequently change, product classifications vary, and filing deadlines differ across states. And the operational burden only increases with each additional registration.

Avalara provides:

• Automated nexus monitoring across all U.S. states, with visibility into when thresholds are approaching or exceeded

• Real-time rate calculation and taxability mapping at checkout, down to state, county, and city level

• Multistate registration management, reducing administrative burden

• Automated return preparation and filing, aligned to each state’s frequency and format

• Exemption certificate management, including collection and validation

• Audit-ready reporting and documentation, with transaction-level traceability

Avalara helps U.K. businesses selling into the U.S. centralise and automate U.S. sales tax compliance. Avalara AvaTax can integrate directly with the ecommerce platforms and ERP systems you already use to calculate accurate U.S. sales tax in real time. Returns, registration support, and certificate management can be managed within the same ecosystem — reducing fragmentation and manual intervention.

If you are expanding into the U.S. — or suspect you may already have triggered U.S. sales tax obligations — speak with Avalara today about supporting your U.S. growth.

FAQ

Do I need to register for U.S. sales tax if I’m selling to the U.S. from the U.K.?

You must register once you create “nexus” in a state. This usually happens when your sales exceed a state’s economic threshold (often $100,000 in revenue or 200 transactions), or if you store inventory in that state. Once triggered, registration is mandatory.

Does Amazon or another marketplace handle U.S. sales tax for me?

Most U.S. states require marketplaces like Amazon and Etsy to collect and remit sales tax on marketplace transactions. However, you may still need to register if you exceed nexus thresholds or sell directly through your own website.

What changed with U.S. import duties in 2025?

Since 29 August 2025, the U.S. de minimis exemption has effectively ended for most shipments. Goods entering the U.S. are generally subject to customs duties, regardless of value. This affects landed cost and pricing strategy.

What happens if I should have registered for U.S. sales tax but didn’t?

States can assess backdated tax, penalties, and interest from the date nexus was triggered. Early review and voluntary disclosure may reduce exposure but delaying action increases risk.