Sales-Tax Nexus for Online Sellers, Explained Simply

Few things blindside online sellers like sales tax. You can owe it in states you've never visited, triggered by sales volumes you didn't realise mattered. Here's a plain-English guide to nexus — what it is, what creates it, and how to stay compliant without losing your weekends.

What "nexus" actually means

Nexus is just a connection strong enough that a state can require you to collect and remit its sales tax. Traditionally that meant physical presence — an office, a warehouse, staff. For e-commerce sellers, the bigger trap today is economic nexus.

Economic nexus: the rule that catches everyone

Since the 2018 South Dakota v. Wayfair decision, US states can require out-of-state sellers to collect sales tax once they cross a sales threshold in that state — regardless of physical presence. A common threshold is around $100,000 in sales or 200 separate transactions into a state in a year, though the exact numbers vary state by state.

Where marketplace facilitators help — and where they don't

Many states now require marketplaces like Amazon and Walmart to collect and remit sales tax on behalf of their sellers. That genuinely removes a lot of the burden for marketplace sales. But it isn't a complete shield:

• Sales through your own website (Shopify, WooCommerce) are usually your responsibility, not a facilitator's.
• You may still need to register and file returns in a state even if the marketplace remits the tax — sometimes reporting $0 of tax due but still being required to file.
• Rules differ by state, so a mix of marketplace and direct sales gets complicated fast.

A practical compliance routine

1. Track sales by state

You can't manage nexus you can't see. Track revenue and transaction counts per state so you know when you're approaching a threshold — before you cross it.

2. Register where you have nexus

Once you cross a threshold, register for a sales-tax permit in that state before you start collecting. Collecting tax without a permit is itself a problem in many states.

3. Collect at the right rate

Rates vary not just by state but by county and city. Your e-commerce platform or a tax-automation tool can apply the correct rate at checkout once you're set up.

4. File and remit on schedule

Each state assigns a filing frequency — monthly, quarterly or annually. Missing a filing, even a zero-dollar one, can trigger penalties.

Does QuickBooks alone handle this?

QuickBooks and similar tools are excellent for recording the financial side, and integrations can pull in marketplace data. But mapping multi-state nexus, registrations and filing calendars is a layer most sellers underestimate. Software tracks the numbers; someone still has to interpret the obligations and file correctly.

The takeaway

Sales-tax nexus rewards businesses that watch the thresholds and punishes those that don't notice them. Track sales by state, register where you cross the line, collect at the right rate, and file on time — or hand the whole mechanism to a team that does this every day so a surprise notice never lands on your desk.