Usage and Billing

Synthflow uses usage-based billing, meaning you only pay for what you use. This page explains how we measure usage, how we price it per plan, and how charges appear on your invoice.

How usage is measured

Calls

Phone calls are billed per second, starting when the human and the AI agent connect and ending when the call terminates. Partial seconds are rounded up to the nearest second.

If a transfer completes successfully, billing stops at the point of transfer. Usage after the transfer is not billed.

How minutes appear on your invoice

Rather than rounding each individual call, we aggregate seconds across calls. Each whole minute that accumulates is reported as a separate billing event on your invoice, so you’re charged fairly for your actual usage. All invoices are available in the Billing Portal under Settings > Plan & Billing.

Here’s how it works:

In this example, four calls totaling 125 seconds produce 2 billing events on your invoice (one per accumulated minute), with the remaining 5 seconds carried over to the next call.

Failed and unanswered calls

Calls with a failed or no-answer status are charged a flat fee of $0.05 per call instead of per-second billing.

Call states

Every call in Synthflow has one of the following states:

Calls marked as paused, spam, or in-progress are not charged on your invoice; they only become billable when they reach a terminal state.

Chat

Chat is converted into billable minutes: every 5 AI-generated messages = 1 billable minute, charged at your plan’s per-minute rate.

Pricing by plan

Pay As You Go

On Pay As You Go, calls are billed per LLM at the following rates:

Separately from LLMs, the voice engine is billed on every PAYG phone call. The voice engine is the combination of your transcriber (speech-to-text) and synthesizer (text-to-speech) providers. The Synthflow Voice Engine is billed at $0.09/min.

Legacy plans (Pro, Growth, Agency)

Legacy plans use a single per-minute rate that combines LLM and voice engine usage. Billing is not broken down by LLM; you only see billable minutes used.

Enterprise

Enterprise customers have custom rates based on their agreement.

Included minutes and overage

Plans that include a monthly minute allowance (e.g. 6,000 minutes) only charge for usage above that allowance. If your total minutes used in the period stay within the included amount, that usage is not billed; only overage is charged. This is clearly reflected on your invoices.

Rollover minutes

When rollover is enabled, any unused included minutes at the end of a contractual period roll over to the following period instead of expiring. This allows high-volume accounts to absorb fluctuations in usage without losing the value of their included allowance.

For example, if you finish the current period with 50,000 unused minutes, those minutes carry over and are added to your included allowance at renewal, giving you more to draw from in the next period.

Billing thresholds

For Pay As You Go and legacy plan customers, we use billing thresholds to ensure timely invoicing as your usage grows. Enterprise plans use custom billing arrangements instead.

How thresholds work

Billing thresholds are triggers, not spending caps. When your unbilled usage reaches $200, an invoice is automatically generated and charged to your payment method. The invoice includes all usage accrued up to the moment it is created, which will always be equal to or greater than $200.

Thresholds are not evaluated in real time. Instead:

• Thresholds are checked periodically (approximately every 30 minutes).
• Metered items have an additional ~1-hour cooldown window.
• Usage continues accruing between checks.

Because of this, the invoiced amount can exceed the threshold, especially for high-throughput accounts.

Example

A customer with a $200 threshold accrues usage rapidly. The system evaluates the threshold at 10:00 AM and finds usage has already reached $458. An invoice is generated for $458, the full amount accrued (not $200).

After the invoice is created, usage tracking resets and continues accumulating toward the next threshold or month-end. You may receive multiple invoices in a single billing period if your usage is high.

Monitoring usage

Your current minute usage is displayed in the sidebar, giving you visibility into your consumption at a glance.

Usage dashboard

The Usage dashboard is available under Settings > Usage. It shows:

• Total events recorded and total cost for the selected period at the top.
• A Voice + Text chart: total events grouped by date, with Day or Week granularity.
• A Cost by Provider chart: cost (or usage) broken down by provider, for example per LLM (e.g. GPT 4.1, GPT 4.1 Mini, GPT 5.2), Synthflow Voice Engine, and text or message simulations.

Subaccount usage and pricing

For subaccounts, call and chat usage is measured the same way as for the parent workspace (minutes, aggregation, and the Usage dashboard). The per-minute rate that applies to each subaccount is determined by the pricing plan that subaccount is subscribed to on your Stripe connected account.

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