Aeion Tax — Zero-API-Fee Tax Calculation Engine
Stop paying $0.15-2.00 per-calculation to Avalara, TaxJar, or Vertex. Enterprise-grade tax computation running locally on your server — compound taxes, product tax classes, exemption certificates, postal code matching, seasonal holidays, and nexus tracking. All included free.
Bring-Your-Own-Rates — No API Fees, No Lock-In
Tax Engine Core Capabilities
Local Computation
Tax is calculated on your own server against your own rate tables — no per-transaction API call, no network round-trip at checkout, and no bill that scales with your traffic. Update rates via a CSV from your accountant whenever they change.
External Provider Fallback
Prefer a live-rate service for specific jurisdictions? Plug in TaxJar, ZipTax, or API Ninjas as an optional fallback — local computation stays the default, and the API only gets called when you explicitly want it to.
Postal Code Matching, Down to ZIP+4
Five matching strategies — exact, prefix, range, list, and regex — let you target a single ZIP+4, an entire metro prefix, or a scattered, non-contiguous list of districts, whichever matches how your jurisdictions are actually drawn.
Product Tax Classes
Assign a tax class to a product once, then override its taxability per jurisdiction — the same T-shirt is taxable in California, exempt in Texas, and partially exempt above $100 in Pennsylvania, all from one product record.
Customer Exemptions
Full or partial exemption certificates, scoped by geography or by product, attached directly to the customer record — a wholesale reseller with a Texas resale certificate on file gets $0 tax automatically, no manual override at checkout.
Compound Taxes
Tax calculated on tax, correctly — state tax first, then county tax on top of the state-inclusive subtotal, then city tax on top of that. Real jurisdictions layer this way, and getting it wrong by even a fraction of a percent is a compliance problem waiting to surface in an audit.
Inclusive Taxes
For VAT-style markets where the sticker price already includes tax, the engine automatically works backward to the net amount and the tax portion — no separate gross/net pricing logic to maintain per region.
Shipping Tax
Shipping is taxed differently almost everywhere — configure the rate per jurisdiction once and every checkout applies it correctly without a special case in your checkout code.
Seasonal Tax Holidays
Set an effective date range once — Texas back-to-school, Florida hurricane-prep — and the exemption activates and deactivates itself automatically every year, including holidays that span a year boundary like Nov–Jan.
Nexus Tracking
The engine watches your sales volume and transaction count against every state's economic-nexus thresholds and tells you the moment you cross one — "you've crossed nexus in Colorado, register by [date]" — so you find out from your own dashboard, not from a state notice.
Audit Ledger
Every calculation — jurisdiction, rate, exemption applied — is written to an immutable log. When an auditor asks "why was this order taxed this way," the answer is a lookup, not an afternoon of reconstruction.
ReDoS Protection
Custom postal-code regex patterns are evaluated safely, with catastrophic-backtracking patterns blocked outright — a badly written pattern from an admin can't take down checkout for every customer behind it.
Why Local Computation Wins — By the Numbers
The same math shown throughout this page, distilled.
$0 Per Calculation
Avalara, TaxJar, and Vertex charge $0.15–$1.00 every time you calculate a rate — 100K calculations a year runs $15K–$100K. Aeion Tax computes locally, so the marginal cost of your millionth calculation is the same as your first: nothing.
12+ Tax Frameworks, One Engine
US state and local sales tax, EU/UK/Norway/Switzerland VAT, GST across Australia/India/Canada/Singapore/New Zealand, and digital-service tax in a dozen-plus jurisdictions — most SaaS and e-commerce businesses never need a second tax vendor.
Nightly Rate Sync, 24-Hour Rule SLA
Rates auto-sync nightly from state DOR feeds, the EU VAT API, and OECD tables; when a jurisdiction changes a rule, it's flagged for compliance review and live within 24 hours of the announcement.
Filing-Ready Reports
Monthly, quarterly, and annual reports are generated pre-formatted to each jurisdiction's filing requirements — e-file directly where supported, export PDF/CSV everywhere else.
Immutable Audit Trail
Every calculation, exemption, and rate change is logged permanently — the same ledger that answers "why was this taxed this way" today answers it three years from now in an audit.
The Per-Calculation Fee Trap
| Provider | Per Calculation | 100K/Year Calculations | Annual Cost |
|---|---|---|---|
| Avalara | $0.15-0.75 | 100,000 | $15,000-75,000 |
| TaxJar | $0.10-0.50 | 100,000 | $10,000-50,000 |
| Vertex | $0.20-1.00 | 100,000 | $20,000-100,000 |
| **Aeion Tax** | **$0.00** | **Unlimited** | **$0.00** |
Postal Code Targeting — Down to ZIP+4
Five postal code matching strategies:
```typescript // 1. EXACT — single postal code { postalCodeType: "exact", postalCode: "90210", // Matches ONLY 90210 }
// 2. PREFIX — wildcard start (all ZIPs in a region) { postalCodeType: "prefix", postalCodePrefix: "902", // Matches 90210, 90211, 90212... }
// 3. RANGE — numeric range (handle split ZIP codes) { postalCodeType: "range", postalCodeRangeStart: "10001", postalCodeRangeEnd: "10099", // Matches 10001-10099 }
// 4. LIST — specific codes (handle non-contiguous areas) { postalCodeType: "list", postalCodeList: ["94102", "94103", "94107", "94108", "94110", "94114"], }
// 5. REGEX — complex patterns (with ReDoS protection) { postalCodeType: "regex", postalCodeRegex: "^[0-9]{5}(-[0-9]{4})?$", // US ZIP or ZIP+4 } ```
ReDoS protection (regex patterns capped at 100 characters):
```typescript // Dangerous patterns are BLOCKED: ❌ /\(\.\\)\+/ // (.)+ — exponential backtracking ❌ /\[\^[^\]]\]\+\+/ // [^...]++ — catastrophic ❌ /\(\?=.\)\*/ // Lookahead + quantifier
✅ /\b\d{5}\b/ // Simple — allowed ✅ /^90[0-9]{3}$/ // Prefix pattern — allowed ```
Jurisdiction specificity ranking:
``` Postal code match: score +8 City match: score +4 County match: score +2 State match: score +1
→ Most specific jurisdiction wins → Rate priority field as tiebreaker ```
Product Tax Classes — Per-Jurisdiction Rules
Tax classes let you handle products differently in different places:
```typescript // Tax class: "clothing" { code: "clothing", name: "Apparel - Clothing", defaultTreatment: "taxable", jurisdictionRules: [ { country: "US", state: "TX", // Texas: clothing exempt treatment: "exempt", effectiveFrom: "2024-01-01", effectiveUntil: "2024-12-31", }, { country: "US", state: "PA", // Pennsylvania: $0-100 exempt, above taxed treatment: "partial", exemptionAmount: 10000, // $100 in cents }, { country: "US", state: "MN", // Minnesota: clothing exempt Nov-Dec only treatment: "seasonal", startMonth: 11, startDay: 1, endMonth: 12, endDay: 31, }, ], }
// Product assignment in commerce: { name: "Premium T-Shirt", sku: "TSHIRT-001", price: 2999, // $29.99 in cents taxClass: "clothing", }
// At checkout in Austin, TX → $0 tax (clothing exempt) // At checkout in Philadelphia, PA → $0 on first $100, $29.99 taxed above // At checkout in Minneapolis, MN in November → $0 tax (seasonal holiday) // At checkout in San Francisco, CA → full state+city tax applied ```
Class overrides in rate definitions:
```typescript // Rate that EXCLUDES a specific class { name: "CA State Tax", rate: 7.25, appliesToAllProducts: false, excludeProductTaxClassIds: ["clothing", "groceries", "prescription"], }
// Rate that INCLUDES only specific classes { name: "Digital Goods Surtax", rate: 3.0, appliesToAllProducts: false, productTaxClassIds: ["digital", "software", "streaming"], } ```
Exemption Certificates — B2B Resale Made Simple
How exemption certificates work:
```typescript // Customer has exemption on file: { id: "exemp_001", customerId: "cust_12345", customerName: "Acme Wholesale LLC", exemptionType: "resale", exemptFromAll: true, // Full exemption // OR for partial: isPartialExemption: true, exemptionPercentage: 75, // 75% exempt, 25% taxed // OR maxExemptAmount: 100000, // First $1,000 exempt
scopeType: "specific_states", // Only in these states: exemptStates: ["TX", "FL", "NV"],
// OR scopeType: "specific_countries", exemptCountries: ["US"],
certificateNumber: "RESALE-TX-2026-001234", documentUrl: "https://...", // PDF of actual certificate expiresAt: "2027-05-11", neverExpires: false, status: "active", } ```
Exemption check at checkout:
```typescript calculateTax({ items: [...], shippingAddress: { country: "US", state: "TX", postalCode: "78701" }, customerId: "cust_12345", });
// → Checks the customer's exemption certificates for an active match // → Acme Wholesale has an active Texas resale certificate on file // → Full exemption applied → $0 tax // → Adjustment logged with a reference to the exemption for audit trail ```
Compound & Inclusive Taxes — Real-World Tax Complexity
Compound tax (tax on tax): California adds city tax on top of state tax:
```typescript // CA State Tax — base rate { name: "CA State", rate: 7.25, isCompound: false }
// Los Angeles County — compounds on state tax { name: "LA County", rate: 2.25, isCompound: true } // → Applied to: subtotal + state tax = $100 + $7.25 = $107.25 // → County tax: $107.25 × 2.25% = $2.41
// Los Angeles City — compounds on county tax { name: "LA City", rate: 1.50, isCompound: true } // → Applied to: subtotal + state + county = $100 + $7.25 + $2.41 = $109.66 // → City tax: $109.66 × 1.50% = $1.64
// Total: $7.25 + $2.41 + $1.64 = $11.30 on $100 // vs simple calculation: ($100 × 11%) = $11.00 // Compound math: $0.30 more — legally correct ```
Inclusive tax (VAT-style): Price already includes tax:
```typescript // UK VAT — price is gross, need net { name: "UK VAT", rate: 20.0, isInclusive: true, // Price already includes tax }
// $120 product with isInclusive=true // → Net amount: $120 / 1.20 = $100 // → Tax: $20 // → Effective rate shown: 20.00% ```
Order value thresholds:
```typescript // France reduced VAT on books under €17 { name: "FR Reduced VAT (Books)", rate: 5.5, appliesToAllProducts: false, productTaxClassIds: ["books"], maxOrderValue: 1700, // €17 in cents }
{ name: "FR Standard VAT (Books > €17)", rate: 20.0, appliesToAllProducts: false, productTaxClassIds: ["books"], minOrderValue: 1701, // Above €17 } ```
Seasonal Tax Holidays — Auto-Activate by Date Range
Seasonal tax holidays, handled automatically:
```typescript // Texas back-to-school holiday (Aug 1-31) { name: "TX Back-to-School Tax Holiday", rate: 0, state: "TX", country: "US", isActive: true, seasonalConfig: { isSeasonal: true, startMonth: 8, // August startDay: 1, endMonth: 8, // August 31 endDay: 31, }, appliesToAllProducts: false, productTaxClassIds: ["clothing", "footwear", "school-supplies"], }
// Florida hurricane supplies holiday (June 1 - Aug 31) { name: "FL Hurricane Preparedness Holiday", rate: 0, state: "FL", country: "US", isActive: true, seasonalConfig: { isSeasonal: true, startMonth: 6, startDay: 1, endMonth: 8, endDay: 31, }, appliesToAllProducts: false, productTaxClassIds: ["emergency-supplies", "generators"], } ```
Handles holidays that span a year boundary:
typescript
// Holiday spans Nov-Jan (e.g., Christmas holiday)
{
startMonth: 11, // November
endMonth: 1, // January
// The date-range check correctly handles wraparound: month > 11 OR month < 1
}
Tax calculation without the per-transaction vendor bill.
Aeion Tax runs compound sales-tax math locally — state, county, and city layers, resale exemptions, and economic-nexus tracking that flags a new filing obligation before a state's Department of Revenue does. Because it runs in-platform instead of billing per API call, tenants can replace metered vendors like Avalara or TaxJar without giving up nexus monitoring or the audit trail: every calculation writes to an immutable ledger your accountant can pull directly.
Frequently Asked Questions
Yes for most tenants. Aeion Tax handles sales tax (US state + local), VAT (EU + UK + Norway + Switzerland), GST (Australia / India / Canada / Singapore / NZ), and digital-service-tax in 12+ jurisdictions. Multi-state nexus tracking, tax-exempt customer handling, and B2B reverse-charge VAT — all built in. For exotic edge cases (high-volume cross-border with VAT MOSS quirks), Avalara/TaxJar may still be needed; for most SaaS + e-commerce, this is sufficient.
Tax rates auto-sync nightly from authoritative sources (state DOR feeds, EU VAT API, OECD rate tables). Rule changes (new state digital tax, VAT-threshold adjustment) flag for compliance review before applying. 24-hour SLA on rate updates from announcement date.
Yes — monthly / quarterly / annual filing-period reports per state / country with the data formatted to that jurisdiction's filing requirements. Most US states accept direct e-filing; for those that don't, the report exports as PDF + CSV for manual filing.
Tax-exempt status tracked per customer per jurisdiction; exemption-certificate upload + verification workflow; per-line-item rules for partially-exempt purchases. Audit trail of exemption usage in case of audit.
Continuous transaction monitoring per state; thresholds (sales count + dollar volume) tracked against each state's economic-nexus rule. When you cross a threshold, the system surfaces a notification: "You've crossed economic nexus in Colorado — register with their DOR by [date]." Doesn't auto-register (you decide), but reminds you in time.
Zero API Fees. Full Tax Compliance.
Stop paying per-calculation to Avalara and TaxJar. Set your rates once, calculate unlimited times. Compound taxes, product classes, exemptions, seasonal holidays, nexus tracking — all included free with Aeion OS.