Introduction
Picture this: you've spent two years building a thriving online store, shipping products to customers across five states. Then a letter arrives from a state tax authority demanding back taxes you didn't know you owed. Interest is accruing. Penalties are stacking. You never even had a storefront in that state.
This scenario catches online sellers off guard every year — and it traces back to one critical shift: the 2018 Supreme Court ruling in South Dakota v. Wayfair, Inc. That decision eliminated the physical presence requirement for sales tax collection. Today, selling enough product into a state — regardless of where your business is located — can legally obligate you to collect and remit sales tax there.
This guide answers the questions that matter most:
- When do you actually owe sales tax in another state?
- What is nexus, and how do you determine if you have it?
- How do you register, collect, and remit correctly?
- What exemptions exist, and what happens if you ignore your obligations?
Key Takeaways
- Sales tax obligations follow your customers' locations, not your business address
- Nexus — physical or economic — determines your legal obligation to collect in each state
- Most states set an economic nexus threshold at $100,000 in annual sales or 200 transactions
- Non-compliance risks include back taxes, interest, penalties, and state-initiated audits
- Exemptions require proper documentation; without valid certificates, liability falls on the seller
What Is Online Sales Tax and Who Needs to Collect It?
Online sales tax is a state-level tax that businesses collect on taxable goods and services sold over the internet, then remit to the appropriate state authority. There is no federal general sales tax. Every state sets its own rules, rates, exemptions, and thresholds — making this a genuinely fragmented compliance landscape.
Five states impose no statewide sales tax: Delaware, Montana, New Hampshire, Oregon, and Alaska. However, Alaska allows local jurisdictions to impose their own sales tax, so don't treat it as universally tax-free. Every other state and the District of Columbia has some form of online sales tax requirement that may apply to your business.
Who Collects — and Why It Matters
When an online seller has a qualifying connection (nexus) to a state, that seller must collect tax from buyers in that state and remit it to the state revenue authority. The buyer doesn't pay it directly, and marketplaces don't always cover it — that responsibility falls on the seller.
Use tax is the complementary obligation here. When a seller doesn't collect sales tax, the buyer technically owes "use tax" to their state. In practice, states rarely enforce use tax on individual consumers — which is exactly why states shifted enforcement to sellers after the Wayfair ruling.
Here's how collection responsibility breaks down in most states:
- Registered sellers with nexus — required to collect and remit sales tax on taxable transactions
- Out-of-state sellers below nexus thresholds — generally not required to collect, though buyer use tax may technically apply
- Marketplace facilitators (Amazon, Etsy, etc.) — required to collect in most states on behalf of third-party sellers
- Buyers without a collecting seller — technically owe use tax, though enforcement against individuals is rare
Understanding Nexus: The Key to When You Must Collect
Nexus is the legal connection between your business and a state that triggers a sales tax obligation. Once you have nexus in a state, you must register, collect, and remit tax there. No nexus means no obligation in that state.
There are two primary types every online seller must evaluate.
Physical Nexus
Physical nexus is created by a tangible business presence in a state. Common triggers include:
- A storefront, office, or warehouse
- Employees or contractors working in-state
- Inventory stored at a third-party fulfillment center
That last point catches many Amazon FBA sellers off guard. If Amazon stores your inventory in a warehouse in Illinois or Texas, you may have physical nexus there — even if you've never set foot in the state.
States apply these rules differently. In 2022, a Pennsylvania court ruled that FBA inventory alone didn't establish physical presence for sellers in that specific case, but outcomes vary by state. Track where your inventory physically sits.
Economic Nexus and the Wayfair Ruling
The 2018 Supreme Court decision in South Dakota v. Wayfair ruled that states can require out-of-state sellers to collect sales tax based on economic activity alone — no physical presence required. By 2021, all 45 states with a statewide sales tax plus DC had adopted remote-seller collection requirements.
The dominant threshold is $100,000 in annual in-state sales, though the specifics vary:
| State Group | Economic Nexus Threshold |
|---|---|
| Most states | $100,000 (sometimes + 200 transactions) |
| Alabama, Mississippi | $250,000 |
| California, Texas | $500,000 |
| New York | $500,000 + 100 transactions |
These thresholds change. Always verify current figures with each state's revenue department — the Sales Tax Institute's state-by-state guide is a reliable starting point, but confirm with official sources before acting.
Other Nexus Types
Physical and economic nexus cover most situations, but three additional categories apply to online sellers with certain partner or platform arrangements:
- Click-through nexus: You have in-state affiliates (bloggers, referral partners) who drive traffic to your site in exchange for a commission
- Affiliate nexus: In-state entities formally promote your business, creating a representative relationship even without direct sales activity
- Marketplace nexus: Platforms like Amazon, eBay, or Etsy may collect and remit tax on your behalf under marketplace facilitator laws — shifting the compliance burden to the platform rather than the seller
Assessing Your Sales Tax Obligations by State
Origin vs. Destination Sourcing
Most states today use destination-based sourcing — tax is calculated based on where the customer receives the product, not where your business is located. This is the more complex standard for multi-state sellers because you're applying the customer's local combined rate (state + county + city + special districts), not a single flat rate.
A smaller number of states use origin-based sourcing for intrastate transactions. For remote sellers, destination sourcing generally controls regardless. Confirm the specifics with each state's revenue department before you begin collecting.
Once you understand which sourcing rules apply, the next step is mapping where you may actually owe tax. Run through this self-assessment quarterly, especially as your sales grow:
A Practical Self-Assessment Framework
- List every state with a physical presence — offices, employees, inventory locations, fulfillment centers
- Track gross sales and transaction count by state for the past 12 months
- Compare against each state's economic nexus threshold — remember thresholds differ
- Flag states where you've crossed or are approaching a threshold — approaching counts, because you need lead time to register before collection begins
Digital Products Are Taxed Inconsistently by State
Not every product is taxable in every state, and digital goods are the most inconsistent category:
- Washington broadly taxes digital goods, digital automated services, and remote-access software
- South Carolina exempts electronically delivered software but taxes streaming content (TV, movies, music) as communications
- Maryland applies different treatment to SaaS depending on individual versus enterprise use
If you sell SaaS, downloadable content, or streaming services, classify your products state by state — a blanket assumption will be wrong somewhere.
How to Calculate, Collect, and Remit Online Sales Tax
Step 1: Register Before You Collect
Registration with a state's revenue authority must happen before you collect a single dollar of sales tax there. Collecting without a permit can itself trigger penalties . In New York, making taxable sales without a Certificate of Authority can produce daily civil penalties capped at $10,000, in addition to all unpaid tax liability.
Registration is done online through each state's tax portal. For businesses with nexus in multiple states, each state has its own timing rules, forms, and requirements — so the workload compounds fast. F.I.C. handles multi-state sales tax filing at $100 per form per state or city, which means a business registered in three states and one city pays $400 total. Our inter-state accounting expertise matters here precisely because no two states handle registration the same way.
Step 2: Apply the Correct Rate
Tax rates vary by state, county, city, and special taxing districts. The GAO has documented over 10,000 sales tax jurisdictions with differing rates and product definitions across the US.
E-commerce platforms like Shopify and WooCommerce have built-in tax calculation tools, but verify rates against official state sources periodically. Colorado is a notable example: it uses destination sourcing, but many home-rule cities self-collect and maintain their own registration and return requirements entirely separate from the state system.
Step 3: Collect and Document
Tax must appear as a separate line item at checkout. Maintain detailed records of every taxable transaction:
- Product sold and its taxability classification
- Customer's shipping address (for destination sourcing)
- Tax amount collected
- Transaction date
These records are your primary defense in an audit.
Step 4: File Returns and Remit on Time
Each state assigns your filing frequency (monthly, quarterly, or annually) based on your sales volume. Larger sellers typically file monthly; smaller sellers may qualify for quarterly filing.
Even when volume is low, two obligations remain:
- Many states still require a "zero return" when you've collected no tax during a period
- Late or missed filings trigger immediate penalties and interest, with no grace period in most states
Step 5: Monitor Obligations Continuously
Compliance isn't a one-time setup. As your business grows, you may cross new nexus thresholds in states where you previously had no obligation. Review your nexus footprint whenever you:
- Launch new product lines
- Enter new markets
- Add or change fulfillment partners
Sales Tax Exemptions and Special Situations
Common Exemption Categories
Three exemption types apply most frequently to online sellers:
- Resale exemptions : buyers who purchase goods to resell can provide a resale certificate, exempting the purchase from sales tax. The Multistate Tax Commission's multijurisdiction resale certificate is accepted by 36 states, simplifying multi-state documentation
- Nonprofit exemptions : qualifying nonprofits with state-issued certificates can often purchase tax-free, but exemption isn't automatic for every nonprofit or every type of purchase
- Manufacturing exemptions : some states exempt raw materials or equipment used directly in production, but the scope varies widely by state
If a customer's exemption certificate is missing, expired, or invalid, the tax liability shifts back to you as the seller. Collect and retain certificates before exempting any sale — this is non-negotiable.
Sales Tax Holidays
Beyond ongoing exemptions, some states create temporary ones. Many states suspend sales tax on specific product categories for limited windows: back-to-school supplies, energy-efficient appliances, and disaster preparedness items are common examples. Texas, for instance, holds an annual tax holiday that explicitly covers qualifying online and remote orders.
Online sellers are generally required to honor these holidays for customers in those states during the designated period. Load holiday dates, eligible products, and price caps into your compliance calendar annually, as schedules change each year.
Marketplace Facilitator Laws
If you sell through Amazon, Etsy, eBay, or Walmart Marketplace, the platform may be legally required to collect and remit sales tax on your behalf. All 45 states with a statewide sales tax have marketplace facilitator laws in place.
However, "the marketplace collected it" doesn't mean you have zero obligations. You may still need to:
- Register independently in states where you have direct sales or physical nexus
- File returns even when the marketplace handles collection
- Retain exemption certificates for your own records
Confirm the platform's collection arrangement in writing. Coverage rarely extends to every jurisdiction or every sales channel, so verify before assuming you're covered.
Consequences of Not Collecting Online Sales Tax
The financial exposure from non-compliance compounds fast. State penalties typically include:
- Percentage-based fines on unpaid tax
- Flat-dollar penalties for failure to register or file
- Accrued interest on outstanding balances
- Additional fees for late filings
A business that unknowingly skips sales tax collection across five states for two years doesn't just owe the original tax — it owes back tax, plus interest that has been accruing the entire time, plus penalty stacks for every missed filing period. Retroactive compliance is almost always more expensive than proactive registration.
The Audit Risk Is Real
States have significantly increased enforcement of online sales tax since Wayfair. Multi-state sellers with inconsistent records are prime targets. Strong recordkeeping — transaction logs, exemption certificates, filing confirmations — is your best audit defense.
If you're already behind, voluntary disclosure programs (VDAs) offered through the Multistate Tax Commission and individual states allow businesses to come forward, correct past errors, and often reduce or waive penalties. Pennsylvania, for example, can waive penalties for up to three years plus the current year under its VDA program. These windows have conditions and close once a state initiates contact — act before that happens.
For businesses with multi-state exposure or past liabilities, F.I.C. handles multi-state sales tax filing at $100 per form. The FIC Package — which bundles sales tax, bookkeeping, payroll, and advisory support — starts at $500/month and covers ongoing compliance across multiple jurisdictions.
Frequently Asked Questions
How does sales tax work for an online business?
Online businesses must collect sales tax in any state where they have nexus — through a physical presence or by exceeding the state's economic nexus threshold (typically $100,000 in annual sales or 200 transactions). Collected tax is remitted to that state's revenue authority on a monthly, quarterly, or annual filing schedule assigned at registration.
Does PA have online sales tax?
Yes. Pennsylvania requires remote sellers to collect sales tax once they exceed $100,000 in annual gross sales to Pennsylvania customers. Marketplace collection doesn't automatically eliminate all obligations — verify product taxability and current thresholds with the Pennsylvania Department of Revenue.
What is the sales tax on online purchases in Colorado?
Colorado imposes sales tax on online purchases with a $100,000 annual sales threshold for remote sellers. Rates vary significantly by location — many home-rule cities self-collect and have separate registration requirements outside the state system. Verify current rates and local obligations through the Colorado Department of Revenue.
Does South Carolina charge sales tax on digital products?
It depends on the product type. Electronically delivered software is generally not taxable in South Carolina. However, streaming content — television programs, movies, and music — is taxable as communications. Certain SaaS and database access services have also been ruled taxable. Verify your specific product category with the South Carolina Department of Revenue before assuming an exemption applies.
What are the penalties for not collecting online sales tax?
Penalties can include percentage-based fines on unpaid tax, flat-dollar penalties for failing to register or file, and interest accruing on all outstanding balances. In New York, for example, selling without a Certificate of Authority can trigger daily civil penalties up to $10,000 — on top of all back taxes owed.
Do I need to collect sales tax if I sell on Amazon or Etsy?
In most states, marketplace facilitator laws require Amazon, Etsy, and similar platforms to collect and remit sales tax on facilitated sales. Confirm this arrangement directly with the platform. You may still have independent registration and filing obligations if you also sell through your own website or have physical nexus in a state.
