Usage and Billing
Synthflow uses usage-based billing, meaning you only pay for what you use. This page explains how we measure usage and how charges appear on your invoice.
How calls are billed
Phone calls are billed by the minute. We measure the actual duration of each call and aggregate usage for billing.
Minute aggregation
Rather than rounding each individual call, we use a carryover system that aggregates seconds across calls. This ensures you’re billed fairly for your actual usage.
Here’s how it works:
In this example, four calls totaling 125 seconds resulted in 2 billed minutes, which is accurate since 125 seconds equals 2 minutes and 5 seconds.
Failed calls are not billed. If a call fails due to a system error, invalid configuration, or network issues, you won’t be charged.
Per-minute rates
Pay As You Go (PAYG)
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.
LLM-based billing and the per-LLM breakdown above apply only to Pay As You Go. On Enterprise and legacy plans (Pro, Growth, Agency), billing is not broken down by LLM; you see billable minutes used only.
Enterprise
Custom rates based on your agreement. Check your specific pricing in Settings > Plan & Billing.
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.
Included minutes and overage billing do not apply to Pay As You Go, which uses a different pricing model.
How chat is billed
Chat messages with AI agents follow a similar usage-based model. Messages are metered and billed according to your plan’s rates. The exact pricing depends on the complexity of the interaction and the underlying model used.
Billing thresholds
For Pay As You Go customers, we use billing thresholds to ensure timely invoicing as your usage grows.
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.
A $200 threshold does not mean your invoice will be exactly $200. If usage grows quickly between threshold checks, the invoice will reflect the full amount accrued at the time of creation. This is expected behavior. If you need hard spending limits, you must implement usage caps on your own — billing thresholds will not enforce a ceiling.
Billing thresholds do not apply to Enterprise plans, which have custom billing arrangements.
Example
A PAYG 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.
For agency accounts with subaccounts, you can view usage breakdowns per subaccount in the Agency dashboard.
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.
Usage shown reflects billable credits only. Credits used during call transfers are not included and may cause differences from other analytics views.
Billing cycle
Invoices are generated:
- Monthly on your billing anniversary date
- At threshold when unbilled usage reaches $200 (PAYG only — invoiced amount may exceed $200)
- On demand for add-on purchases
All invoices are available in the Billing Portal under Settings > Plan & Billing.
FAQ
Are failed calls charged?
No. You’re only charged for successful calls that connect. Calls that fail due to errors, invalid numbers, or system issues are not billed.
How do I see my current usage?
Your current minute usage is shown in the sidebar. For detailed usage history — including total events, total cost for a period, and breakdown by date and by provider — use the Usage dashboard under Settings > Plan & Billing. Invoices and full billing history are in the Billing Portal there.
Why doesn't the usage dashboard match my other analytics?
Usage on the dashboard reflects billable credits only. Credits used during call transfers are not included, which can cause differences from other analytics views.
Why did I receive multiple invoices this month?
If your usage exceeded the $200 billing threshold, an additional invoice was generated mid-cycle. This is normal for high-volume usage and helps avoid large end-of-month charges.
Why is my threshold invoice more than \$200?
Billing thresholds are triggers, not caps. Thresholds are checked periodically (roughly every 30 minutes), so usage can grow beyond $200 before an invoice is created. The invoice covers all usage accrued up to that point. This is expected behavior — not an overcharge.
Can I set usage alerts?
Usage alerts are not yet available but are on our roadmap. For now, monitor your usage through the sidebar indicator.
How is international calling priced?
International calls may have different per-minute rates depending on the destination. Check your specific rates in Settings > Plan & Billing or contact support for details.
Do carryover seconds reset?
Carryover seconds accumulate throughout your billing period. At the end of each billing cycle, any remaining carryover is included in that period’s final invoice.
