Rooftop address resolution, boundary-verified filing jurisdictions, product taxability, and source-pinned rates — not a ZIP-code average.
The Sales Tax Engine: Real-Time Determination, Separated from Compliance
We pulled tax calculation out of the compliance workflow and made it a product. The Sales Tax Engine determines sales tax before a transaction is finalized, returns the result to the system that asked, and preserves every determination — inputs, sources, and money math — for the compliance work that follows.
Calculate through the documented API today, connect billing and accounting data sources, and hand completed determinations to Sales Tax Compliance at period close — where they are checked again before a return is prepared. The production engine is $99/location through a sales-assisted integration, and its content layer also powers the public Sales Tax Atlas.
Quote, apply to the draft, commit with the completed document, and follow refunds, voids, and adjustments through the same lifecycle.
Inputs, resolved jurisdiction, content source, and line-level money math are retained; Compliance re-checks them at period close.
One determination pipeline, used by every surface
The same resolution and content pipeline serves the API, uploads, connected systems, and the public Sales Tax Atlas — so the answer cannot differ by door.
Address resolution
Validation, normalization, and rooftop geocoding through an ordered provider chain; every result records which provider resolved it and why.
Jurisdiction resolution
A filing-jurisdiction spine maps the rooftop point to the state’s official filing code, with a pure point-in-polygon boundary check against committed Census geography — city limits, not city mailing names.
ship_to → rooftop lat/lon → boundary feature → filing jurisdiction codeClassification and taxability
Product identity is established before a rate is chosen: tax codes, exemption context, and separately-stated shipping classified per jurisdiction rule.
Rate and rule content
An ordered content chain resolves the governing rate from source-pinned registries — the same reviewed content published in the Sales Tax Atlas.
Line money
One calculation engine computes every line the same way on every route — and when an answer cannot be fully verified, it is routed to review instead of guessed.
POST /api/v1/tax/calculateDocument semantics
Seller-side semantics, shipping allocation, marketplace responsibility facts, and tax-owner identification complete the document before anything is applied.
How the Sales Tax Engine compares
Tax engines are usually judged on integrations, content, and control. Here is the honest picture.
| Compare | Prophit.ai Sales Tax Engine | Avalara AvaTax | Vertex O Series | Sovos Global Tax Determination |
|---|---|---|---|---|
| Positioning | API-first determination engine, separated from — and feeding — a connected compliance workflow | Cloud tax engine with a large connector ecosystem across the compliance lifecycle | Enterprise determination engine for complex jurisdictional and product rules; deep ERP deployments | Global determination engine oriented to multi-country VAT/GST mandates and regulatory reporting |
| Content transparency | Public: the Sales Tax Atlas publishes the engine’s content layer — 51 state guides, 8,000+ product-treatment research records, and 3,800+ local rate pages with official source pins anyone can audit | Proprietary tax content | Proprietary tax content | Proprietary tax content |
| Purchasing-side engine | A separate Use Tax Engine for procurement determination and approved accrual write-back | Consumer use tax available as a separate product | Consumer use tax within the O Series suite | Use tax handled within the determination suite |
| Pricing model | Published flat pricing: the production Sales Tax Engine module is $99/month per location through sales-assisted setup with 10,000 calculations/month included; platform plans are flat per organization ($199/$599 per month) | Usage-based; plans start at $699 per state, per year | Custom quote only | Custom quote only |
| Compliance handoff | Committed determinations flow to Sales Tax Compliance at period close, where situs, taxability, responsibility, and return treatment are checked again before a return is prepared | Feeds Avalara returns products | Feeds Vertex compliance products | Feeds Sovos filing services |
| Best fit | Teams that want a reviewable, evidence-first engine with a public content trail and one platform for engine + compliance | High-volume sellers standardizing on the largest connector catalog | Large enterprises with complex ERP landscapes and dedicated IT | Multinationals with e-invoicing and cross-border mandates |
Competitor characterizations reflect each vendor’s public positioning as of August 2026 and can change; confirm current capabilities with each vendor. Prophit.ai claims are verified against the shipped engine code. Sources: Avalara AvaTax, Vertex O Series, Sovos.
Calculation and compliance are different jobs. We stopped pretending otherwise.
A compliance platform reviews what happened last period. An engine has to answer in the moment a transaction is created — in checkout, billing, or the ERP — and then make that answer durable. Bolting the two together forces one of them to compromise. So we separated them: the Sales Tax Engine determines and returns tax in real time; Sales Tax Compliance consumes the committed determinations at period close and independently re-checks situs, taxability, responsibility, and return treatment before any return is prepared.
Determine before finalization
The engine answers while the document is still a draft — before the customer is charged.
Return to the source system
The determination goes back to the system that asked and stays bound to the completed document.
Follow the document’s life
Quote, apply, commit, adjust, refund, void — the calculation follows the transaction, not the other way around.
Fail closed, not silent
Unresolved addresses, ambiguous products, and unknown marketplace responsibility block application instead of guessing.
Evidence by default
Inputs, resolved jurisdiction, content sources, and line math are preserved for review and audit.
Compliance double-checks
Period close re-verifies every committed determination — the engine never bypasses filing controls.
The Atlas is the engine’s content layer, published.
Most tax engines ask you to trust a black box. Ours publishes its content layer: the Sales Tax Atlas — 51 state and DC guides, more than 8,000 state-specific product-treatment research records, over 3,800 county and city rate pages, and 2026 filing calendars — every page pinned to the official source it came from. The rates the Atlas shows are resolved by the same content chain the engine uses. When you want to know what the engine will say, you can read it first.
Sales Tax Atlas
51 state guides with rates, sourcing, forms, marketplace treatment, and official sources.
Browse the AtlasLocal rate pages
3,800+ county and city combined rates with source pins and effective dates.
See a state’s local ratesSales tax calculator
The engine’s rate resolution, exposed as a free lookup.
Try the calculator2026 filing calendars
Every state’s due dates, weekend/holiday-adjusted, from the same governed rule set.
Download the calendarConnect the system that creates the transaction.
The engine is API-first: anything that can make an HTTP call can calculate. Named connectors add managed data flows on top. We label integration status precisely — what is live today, and what is in development — because a tax engine that overstates its connectors is a tax engine you cannot trust.
Prophit.ai API — live
POST /api/v1/tax/calculate for real-time determination and /tax-engine/provider-quotes/apply to calculate and apply to a provider draft with an idempotency key and an auditable binding.
API documentationFile upload — live
Route uploaded sales data into the engine for calculation when a direct connection is not available.
QuickBooks Online — live (sales activity)
Invoices, sales receipts, credit memos, and refund receipts flow in for engine review and validation.
Stripe — live (billing)
Invoices, credit notes, and refunds connect for review and validation; committed lifecycle events reconcile back to the original calculation.
Workday — live (customer invoices)
Customer invoice lines connect for observation and validation.
In development
In-checkout real-time apply for QuickBooks, Workday, and Shopify, and Stripe payments, Connect-marketplace, and settlement profiles are under active development with defined integration contracts. Not live today — talk to us about the roadmap.
Expected tax is not the same as who collects it.
The engine carries explicit marketplace responsibility facts on every calculation. A provider name never silently decides facilitator responsibility; unknown or contradictory responsibility fails closed. Facilitator statements remain first-class evidence alongside real-time connections, and jurisdiction rules keep controlling nexus and return treatment for seller and facilitator roles.
Responsibility is a fact, not an inference
Merchant-of-record, calculation, collection, remittance, and reporting responsibility are effective-dated and reviewable per channel account.
Statements stay canonical
Facilitator statements keep their file hash, period, and mapping — connectors add a source, they never overwrite evidence.
Fails closed
Pre-commit application is blocked while responsibility or calculation facts are unresolved.
Built like money code, because it is money code.
Every line amount comes from a single pure function shared by every route. State rate content ships behind byte-pinned golden test suites, money-parity “killer” tests attack the arithmetic on purpose, and a replay corpus recomputes real vendored state content against the engine on every change. When a state can’t be answered from verified content, the engine says so instead of improvising.
One money function
A single stateless line-money implementation serves the API, uploads, and connected systems — no per-surface forks.
Golden state suites
Per-state golden tests pin rates and boundaries to vendored official bytes, byte-reproducibly.
Adversarial money tests
Dedicated test suites actively try to break rounding, allocation, and shipping calculations on every merge.
Never a hidden guess
When a determination cannot be fully verified, the engine says so and routes it to review — conservatively and visibly.
A cockpit for the people who own the number.
The production Sales Tax Engine workspace shows the calculation pulse, the stream of recent determinations with line-level tax detail, connected data sources, and the apply lifecycle: what was sent back to checkout or billing, what is waiting, and what needs attention. At period close, one click hands the completed calculations to Sales Tax Compliance.
Cockpit
Live status, recent tax calculated, effective rate, and calculation trend at a glance.
Data sources
Connect checkout, billing, marketplace, or uploaded sales data; each source shows its last activity.
Calculation
Every transaction the engine calculated — address, treatment, and tax amount, down to the line.
Apply
Tax sent back to the source system, including refunds, voids, corrections, and errors.
The engine is one door into the same platform.
Determinations flow into compliance; certificates inform taxability; the purchasing side has its own engine. Explore the rest of the platform the engine feeds.
Use Tax Engine
Real-time use-tax determination for procurement, with approved accrual write-back.
Explore the Use Tax EngineSales Tax Compliance
Period review, reconciliation, and filing-ready returns built on committed determinations.
Explore complianceSales tax API
The developer surface for the engine — documentation, sandbox, and scoped keys.
Explore the APIExemption certificates
Certificate status feeds taxability on both sides of the business.
Explore certificatesSales tax software, compared
How the whole platform stacks up against Avalara, TaxJar, Vertex, and Anrok.
See the comparisonCommon questions.
What is a sales tax engine?
A sales tax engine is software that determines the correct sales tax for a transaction in real time — resolving the address to the governing jurisdictions, classifying the product, applying the current rates and rules, and returning the amount to the system that created the transaction (checkout, billing, or ERP). It differs from compliance software, which reviews completed transactions and prepares returns after the fact.
How is the Sales Tax Engine different from Prophit.ai’s compliance modules?
The engine answers in the moment and returns tax to the source system; compliance consumes the committed determinations at period close and independently re-checks situs, taxability, marketplace responsibility, and return treatment before a return is prepared. They are separate modules by design — the engine never bypasses filing controls.
How do I integrate the Sales Tax Engine today?
Through the documented API — POST /api/v1/tax/calculate for real-time determination, and the provider-quote endpoint to calculate and apply tax to a provider draft with an idempotency key — or by connecting QuickBooks Online sales activity, Stripe billing, or Workday customer invoices as data sources, or by uploading sales data. In-checkout real-time connectors for QuickBooks, Workday, and Shopify are in development.
Does it integrate with SAP or Oracle?
SAP and Oracle integrations are defined for the purchasing side: the Use Tax Engine’s SAP and Oracle profiles (procurement calculation and accrual write-back) are in development with published integration contracts. Workday purchasing documents connect today. If you run SAP or Oracle, talk to us about the integration roadmap.
How accurate are the rates?
Rates come from source-pinned content registries reviewed against official state sources, and the same content is published publicly in the Sales Tax Atlas — 51 state guides and 3,800+ local rate pages with source links and effective dates — so accuracy is auditable rather than asserted. Per-state golden test suites pin the served content to vendored official bytes.
What happens to a calculation after checkout?
It stays bound to the document. Commits, adjustments, refunds, and voids append lifecycle events to the original calculation, and completed determinations flow to Sales Tax Compliance at period close for independent re-checks and return preparation.
What does the Sales Tax Engine cost?
The Sales Tax Engine is $99/location, with 10,000 calculations per month in the published module envelope. Setup is sales-assisted so source-system scope, credentials, and controls are confirmed before activation. There is no per-state fee.
Is this a rate-lookup API?
No. A rate lookup returns a number for a ZIP code. The engine resolves the rooftop address to boundary-verified jurisdictions, establishes product identity before choosing a rate, computes line-level money with documented rounding and allocation, carries marketplace responsibility facts, and preserves the whole determination as evidence. The free calculator and Atlas expose the lookup layer; the engine is the full pipeline.
Put a real determination engine behind your transactions.
Start with the API documentation, or plan the production integration and control setup with the team.
- Production standalone Sales Tax and Use Tax Engines ($99/month per location through sales-assisted setup, with 10,000 calls/month included) return determinations to source systems through an API.
- The tax content is published and auditable: the Sales Tax Atlas carries 51 state and DC guides and 3,800+ county and city rate pages, each pinned to its official source.
- AI-native since 2019: AI reads your documents, classifies every transaction for taxability, validates exemption certificates, and answers questions in-app — checked against published state rules, with a person approving every material decision.