Every purchase line carries what the vendor charged and what the jurisdiction, product, and exemption facts say should have happened.
The Use Tax Engine: Determine Use Tax While You Purchase, Not at Audit
Use tax is the tax your vendors didn’t charge. Most companies find it years later, in an audit. The Use Tax Engine determines it during purchasing — vendor-charged tax versus the treatment the purchase, location, product, and exemption facts actually require — and prepares approved accrual outputs while the period is still open. Posting those outputs inside the source accounting system depends on its validated implementation.
A production engine for the purchasing side at $99/location, because procure-to-pay is not order-to-cash: different documents, different evidence, different failure modes. Determinations feed Purchasing Tax Compliance at period close for independent review before anything is filed. Setup is sales-assisted.
Under-charged tax becomes a supported use-tax accrual; over-charged tax becomes a documented correction or recovery candidate.
Exports and API results carry approved accruals into the customer’s accounting implementation. Native source-system posting and receipt confirmation are available only after that write-back path is validated.
The same determination pipeline, pointed at procurement
The Use Tax Engine shares the platform’s resolution and content pipeline — addresses, jurisdictions, taxability, source-pinned rates, one line-money function — and adds purchasing-side semantics on top.
Ingest the purchase
Supplier invoices, purchase orders, and journal lines arrive from a connected system, an upload, or the API.
Resolve the taxing situs
Ship-to and use locations resolve through the same rooftop-and-boundary jurisdiction spine the sales engine uses.
Classify the purchase
Product identity, exemption facts, and vendor certificate context are established before any treatment is chosen.
Determine expected tax
Source-pinned rates and rules produce the expected tax for the line; vendor-charged tax is compared against it.
vendor_charged − expected = accrual candidate (or overpayment)Accrue or correct
Under-collection becomes a supported use-tax accrual; over-collection becomes a documented correction — each with the evidence attached.
Prepare the accounting handoff
Approval rules you configure run first; the engine then makes approved amounts available through exports and API results. Native posting and receipt confirmation require a customer-specific integration validated in the customer tenant.
quote → accrue → commit → export_or_apiUse tax is where audits find their money.
Sellers get sales tax wrong loudly — customers complain. Buyers get use tax wrong silently: a vendor undercharges, nobody notices, and the liability compounds until an auditor totals it with interest and penalties. The only durable fix is determining use tax when the purchase happens, with the evidence attached, and accruing it while the period is still open.
Vendors get it wrong in both directions
Under-charged tax is your liability; over-charged tax is your money, silently gone. Both need line-level detection.
AP systems don’t know tax
ERP and AP workflows record what the vendor billed — they don’t independently determine what the law required.
Audit math is unforgiving
A small per-invoice miss, multiplied across years of spend, is exactly what auditors sample for.
Spreadsheets don’t scale
Manual accrual reviews sample a fraction of spend; an engine evaluates every line.
Connect procurement where it lives.
API-first like its sales-side sibling, with named connectors labeled by their real status — live today or in development. Overstated connectors are how tax software loses trust; we don’t.
Prophit.ai API — live
Governed, stateless calculation for purchasing documents through the documented API.
API documentationFile upload — live
Bring AP extracts, invoice files, and spend data into the engine when a direct connection is not available.
Workday — live (purchasing documents)
Supplier invoice lines and purchase order lines connect for observation and validation today.
SAP — in development
Procurement calculation and accrual write-back for supplier invoices, purchase orders, and journal lines, with a published integration contract. Not live today.
Oracle — in development
Payables calculation and accrual write-back with the same lifecycle contract. Not live today.
QuickBooks & Stripe
Sales-side data sources live on the Sales Tax Engine; purchasing-side profiles follow the same roadmap discipline.
See the Sales Tax EngineCertificates are facts the engine actually uses.
Purchasing-side exemption certificates — the ones you issue to vendors — change what should have been charged. The engine evaluates vendor-charged tax against certificate status, so an exempt purchase billed with tax surfaces as a correction instead of disappearing into spend.
Certificate context at determination
Exemption status informs the expected-tax side of every comparison.
Explore certificate managementVendor overcharge detection
Tax charged on exempt purchases becomes a documented recovery candidate.
Explore Risk & RecoveryUse tax software, the workflow view
How the purchasing compliance workspace consumes what the engine determines.
Explore use tax softwareSee the accrual position while you can still change it.
The production Use Tax Engine workspace shows connected purchasing sources, every calculated line with its address, treatment, and tax delta, and the accounting-handoff lifecycle: prepared amounts, review status, and export or API delivery status. A customer-specific connector can add native posting confirmation only after it is validated in the customer tenant. At period close, Purchasing Tax Compliance takes over with its own checks.
Cockpit
Calculation pulse, recent use-tax determined, and effective rate across recent spend.
Data sources
Connect purchasing, ERP, AP, or uploaded spend data; each source shows its last activity.
Calculation
Every purchase line the engine evaluated, with vendor-charged versus expected tax.
Accounting handoff
Approved accruals and corrections prepared for export or API delivery — completed, waiting, and needs-attention.
One platform, both directions of indirect tax.
The Use Tax Engine feeds purchasing compliance the same way the Sales Tax Engine feeds sales compliance — separate engines, one evidence standard.
Sales Tax Engine
Real-time determination for checkout, billing, and ERP on the sales side.
Explore the Sales Tax EnginePurchasing Tax Compliance
Period review, reason-coded corrections, and filing-ready purchasing outputs.
Explore purchasing complianceTax-exempt purchasing software
What to look for when comparing vendors on the exempt-purchase workflow.
Compare vendorsPricing
Published flat price: $99/month per location through sales-assisted setup, with 10,000 determinations/month included.
See pricingCommon questions.
What is a use tax engine?
A use tax engine determines consumer use tax on the purchasing side: for every purchase line it establishes the taxing jurisdiction, the product’s treatment, and exemption facts, compares the tax the vendor charged with the tax the law expected, and turns the difference into a supported accrual (under-charged) or a documented correction (over-charged) — during the period, not at audit.
How is this different from use tax compliance software?
The engine determines tax in-period and makes approved results available through its API and exports; Purchasing Tax Compliance reviews the committed results at period close — reason codes, reconciliation, and filing-ready outputs — with its own independent checks. Prophit.ai ships both, as separate modules, so determination speed never compromises review rigor.
Does it write accruals into my ERP automatically?
Not through a generic out-of-the-box posting connection. The engine provides approved accrual results through its API and exports. Workday purchasing documents can be imported today for determination and period-close review; native Workday posting requires a customer-specific implementation that is validated in the customer tenant before activation.
Which systems does the Use Tax Engine integrate with?
Today: the documented Prophit.ai API, file uploads, and Workday purchasing documents (supplier invoice lines and purchase order lines). In development, with published integration contracts: SAP and Oracle procurement calculation and accrual write-back, and a Workday real-time profile. If you run another P2P stack, the API is the front door.
Can it find vendor overcharges too?
Yes — the same comparison that surfaces under-accrued use tax also surfaces tax charged on exempt or non-taxable purchases. Overcharges become documented correction or recovery candidates, with Risk & Recovery available for historical review at scale.
What does the Use Tax Engine cost?
The Use Tax Engine is $99/location, with 10,000 calculations per month in the published module envelope. Setup is sales-assisted so procurement scope, credentials, review rules, and write-back authority are confirmed before activation. There is no per-state fee.
Stop discovering use tax at audit.
Plan a purchasing-side integration, or start with the API documentation.
- 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.
- Sales-side and purchasing-side exemption certificate management are included in every plan, or standalone from $49/month per side.
- Human review is a designed control: filing-ready outputs are approved by a reviewer, and unresolved facts fail closed instead of being guessed.