Program fundamentals
CSP vs CAS vs standard sales tax software: what is the difference?
Simplify Sales Tax. Last updated 2026-09-01. Sources last verified 2026-08-21.
A Certified Service Provider (CSP) is a company the member states certified to run your sales tax and file your returns, and where you qualify that state pays it instead of you. A Certified Automated System (CAS) is certified software: it works out the tax and you still file. Non-certified software calculates too, and carries none of the program’s liability relief.
The buying question isn’t which of the three is better software. It’s who does the work, and who carries the loss when a number comes out wrong. A Certified Service Provider isn’t an alternative to a certified system, it operates one: a provider is the certified engine plus an agent who files.
What is the difference between a CSP, a CAS, and non-certified software?
Table: what separates a Certified Service Provider, a Certified Automated System, and non-certified sales tax software under the Streamlined Sales Tax program. Checked August 21, 2026.
| What you’re comparing | Certified Service Provider (CSP) | Certified Automated System (CAS) | Non-certified sales tax software |
|---|---|---|---|
| What you’re buying | A company the member states certified to run your sales tax as your agent, other than tax on your own purchases | Software the member states certified to work out the tax on a sale, decide what to remit, and keep the record | An ordinary commercial product, sold outside the program |
| What gets certified | The company, on a contract with the Streamlined Sales Tax Governing Board | The software itself | Nothing. Certification exists only inside the program |
| Who does the filing | The provider, which also maps your catalog, calculates the tax, sends the money, and answers notices and audits | You. It calculates, the returns stay yours | You, or whoever you pay |
| Who pays for it | The member states, in the states where you qualify. Anywhere else the provider can bill you | You buy it. Member states where you had no requirement to register pay you an allowance for up to 24 months | You, everywhere |
| What the states cover when the tax is wrong | An error that traces to the state’s own rate, boundary, jurisdiction, or taxability data. Not a product filed under the wrong category | An incorrect calculation, on the strength of the states’ certification of the software. Not your product mapping, and not your filing | Nothing from the program |
| Where any of it applies | The member states you registered in | The member states | Anywhere you run it, with no standing in the program |
That’s 24 of the 45 states with a general sales and use tax: 23 full members plus Tennessee, the only associate member.
Does it matter which one you buy?
It matters inside the 24 Streamlined member states and barely anywhere else. Inside them the difference is money and exposure: who files, who the state pays, and whose determination carries relief when the state’s own data was wrong. Outside them all three are software you pay for, and none of them changes what you owe: the Agreement standardized how the member states administer sales tax, not what they tax.
One cost to price before you sign either certified route: a provider runs its own certified engine, so appointing one usually means moving your calculation off whatever you run today.
Who carries the loss when the tax is wrong?
Relief gets oversold on vendor calls. Where a certified system charged the wrong amount because a member state’s own rate, boundary, jurisdiction, or taxability data was wrong, the state carries it rather than you. That’s the risk transfer you’re buying.
It stops at classification. “You will not receive liability relief if you or the CSP incorrectly classify your product into an incorrect product category or to an incorrect tax rule.” Mapping your catalog to the states’ product categories is the step with judgment in it, and relief doesn’t reach it. A provider that did your mapping owns those errors. Where you did the mapping, it can bill you to put things right. Sovos says the same on its own site: relief is not absolute.
Non-certified software has nothing in the program to attach relief to, because relief runs off the states’ certification of the software itself. That is program status rather than product quality, and the calculation stays your exposure. Either way, some obligations survive signing with a provider.
Who pays, and which direction does the money run?
With a CSP, the states pay, in the states where you qualify. Your provider keeps a percentage of the tax you report and pay on time. Qualifying is decided state by state, on where your property and your people sit, which is the CSP-compensated seller test. It can still bill you where you don’t qualify, in states outside the program, and once too much of your volume in one state is non-taxable, which what a certified provider costs explains.
With a CAS, you buy the software, and the state money runs to you rather than to a vendor. Member states where you had no legal requirement to register pay you an allowance for up to 24 months after you register. It’s time limited, which is the part to model: two years in, it’s a line item like any other.
With non-certified software, you pay for all of it, everywhere.
Which of the six certified providers offers a CAS?
Just one of the six. The Governing Board’s own page on certified software states that “Sovos is the only CAS provider under contract with the SSTGB.”
Appoint Sovos as your provider instead and that route closes: Sovos publishes that its CSP customers have to use Sovos for calculation and for filing and remittance.
Certification attaches to a named system rather than to everything a company sells, so the question worth putting to a vendor is which engine actually calculates your transactions. It isn’t always the certified one. TaxCloud’s own integration pages state that on Shopify the calculation is handled by Shopify Tax, and on Stripe by Stripe Tax. Those are the publisher’s own pages, the only ones we checked, as published on August 19, 2026. All six sit on the six certified providers side by side.
What a CSP, a CAS, and non-certified software all leave with you
The states certify a system. They don’t certify the answer it gives you, and four things stay on your desk whichever of the three you buy.
- Product mapping is where the bills come from. Relief stops at the category your catalog sits in, so a product filed under the wrong tax rule costs you money in all three arrangements, and if you did the mapping yourself, correcting it is billable.
- Your taxability positions survive all three. Whether what you sell is taxable in a member state is still that state’s call, and still yours to get right.
- Outside the member states you are buying ordinary software. The distinction pays off only in the member states you registered in, so if most of your filings sit outside the program, this choice moves a smaller number than it looks like it should.
- Tennessee is the open question. It is the program’s only associate member, and whether the states’ funding of providers reaches an associate member has no published answer, so plan against the full member states where you qualify.
None of this is legal or tax advice. Put these questions to each provider directly, and get the answer in writing.