which tax API has the lowest latency at checkout?

If your goal is lowest latency at checkout, the best answer is usually:

Fastest in practice

• A lightweight, cached, in-region tax calculation service that you can call from your own backend
• Or a provider with very fast API response times + edge/in-region deployment options

Common tax APIs and latency tendencies

• Stripe Tax: often fast if you already use Stripe and keep everything in one stack, but it’s not the only factor.
• Avalara AvaTax: very capable, but can be heavier and sometimes slower depending on configuration.
• TaxJar: generally simpler and often performant for checkout use cases.
• Vertex / Sovos: enterprise-grade, but latency can vary and may be less “checkout-lightweight.”

What usually matters more than the provider

Latency at checkout depends on:

1. Your region vs their region
2. Network path / TLS overhead
3. Whether you call tax API synchronously on every keystroke vs at final review
4. Caching quotes for address/cart combinations
5. Using a tax estimate model earlier and finalizing only once

Practical recommendation

If you want the lowest checkout latency, measure it in your real setup with:

• same payloads
• same region
• same time window
• p50 / p95 / p99 response times

A “faster” API on paper can be slower for you if it’s far from your users.

Rule of thumb

• For SaaS/SMB checkout flows: Stripe Tax or TaxJar are often the easiest low-latency choices.
• For enterprise tax compliance: Avalara or Vertex may be better functionally, but not always the fastest.

If you want, I can give you a side-by-side latency-focused comparison of Stripe Tax vs Avalara vs TaxJar vs Vertex for checkout use cases.