How Retell AI Billing actually works

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If you're building voice AI agents for clients, you need to understand how billing really works. Because it's not as simple as "charge per minute."

Retell AI's billing model has hidden complexity:

The base model is per-minute pricing. But it also includes per-message pricing and monthly fees.

On top of that, there are two exceptions most people miss:

Exception 1: Dynamic opening minimum.

If your AI speaks first and the call ends in under 10 seconds, you're still billed for 10 seconds. That 6-second hang-up? Billed as 10 seconds.

Exception 2: Long prompt surcharge.

When your total LLM context exceeds 4,000 tokens, your billed duration gets scaled up.

The formula: Billed duration = actual duration × (tokens ÷ 4,000)

A 2-minute call with 8,000 tokens? You're paying for 4 minutes.

Retell bills each workspace separately, which means a card, credit balance, or invoice in one workspace does not apply to another, even under the same login.

A card added to one workspace does not automatically become available in another. Add a payment method to each workspace before running calls.

So it's wise to use separate workspaces for each client to keep billing separate and easy to manage.

Retell AI separates its charges into usage charges and monthly subscription charges.

#1 Calls, chat messages and other metered activity are paid for using prepaid credits. Retell deducts these charges from your credit balance in real time as you use the service.

#2 The following items are charged to your card at the end of each calendar month and appear on your monthly invoice:

Phone numbers purchased through Retell.
Knowledge bases beyond the free tier.
Calls-per-second (CPS) upgrades.
Additional concurrency (the ability to handle more calls simultaneously).

Note(1): Anything added partway through the month is prorated, meaning you pay only for the portion of the month it was active.

Note(2): Enterprise workspaces remain on monthly invoicing.

Through the ‘Billing’ menu:

#1 You can see how the cost is split by: Voice Engine, Voice LLM, Text LLM, Features used, TTS, LLM Token Surcharge, Concurrency, etc.

#2 You can download a Stripe invoice for a particular month:

Note: You can download monthly invoices from Stripe for the whole workspace and see itemised categories, but not native client‑by‑client splits.

#3 You can delete your account:

#4 You can add a purchase order to subsequent invoices:

#5 You can change payment methods (like credit card):

#6 You can update billing information (name, email, etc.).

#7 You can see usage and cost at the workspace level (but not per client/agent level):

The ‘Usage’ tab shows total cost for the selected period, total call minutes, and average cost per minute so you can monitor efficiency.
The ‘Usage’ tab also shows daily or weekly call costs and costs by provider (voice engines, LLMs, telephony, concurrency) to spot spikes and optimise configuration.

Note(1): Retell AI cost is NOT split by Per Voice Agent or Per Client.

Note(2): There are no fees for just using the Retell AI Platform.

Important points about Retell Credits.

# Credits must be added before calls can run.

# Credits are workspace specific. You can't use credit balance meant for one workspace in another workspace.

# You can buy credits in the Billing tab. Payments are charged to your card through Stripe.

# Your credits never expire, but they are also non-refundable.

# New Retell accounts receive $10 in free trial credit, once per email address.

# Switching to prepaid credits does not provide another $10 trial credit.

# If your credit balance reaches zero, calls and chat stop immediately. Affected calls are logged as credit_exhausted.

# If you want to use your remaining credits, spend them before closing the workspace. Unused credits are non-refundable.

Always enable ‘Auto Recharge’ for each Retell Workspace.

To avoid call interruptions when your credit balance runs out, enable 'Auto Recharge ', which adds credits automatically when your balance falls to a level you choose:

Note: You can’t set ‘when credits drop below’ to less than $10 or ‘Bring credits back to’ below $20.

The target balance must be higher than the recharge trigger. Each recharge is charged to your card.

For example, if your trigger is $50, then your target balance must be higher than $50.

If your target balance is $200, Retell purchases enough credits to bring your balance back to $200 when it reaches the trigger.

Note: For high call volumes, set both amounts higher. If a recharge payment fails, your service can still stop when the remaining credits run out.

Use Budget Setting to set a monthly spending limit for your Retell Workspace.

Retell workspaces have a Budget Setting, which lets you set a monthly spending limit.

You can choose a limit between $10 and $100,000, in $10 increments.

Email alerts are sent when spending reaches 80%, 50% and 100% of the limit.
You can add up to four additional alert thresholds.
At 100%, calls and API requests pause, even if you still have credits available.
Affected calls are logged as budget_reached.

Usage resumes when you raise or remove the cap, or when the next calendar month begins according to UTC.

Note: Auto recharge adds credits; it does not increase or remove your monthly budget cap.

The monthly budget setting acts as an automatic cutoff during a toll-fraud attack.

Toll Fraud (also called International Revenue Sharing Fraud) involves fraudsters tricking people or companies into making very expensive calls (or SMS messages) to special international or premium‑rate numbers they control.

The phone companies involved then share the revenue from those pricey calls with whoever owns those numbers, so the attacker gets a cut of every minute your AI Agent spends calling them.

An attacker finds a way to trigger outbound calls from your account (stolen API key, weak auth, misconfigured telephony) and directs calls to high‑tariff or revenue‑sharing numbers they control overseas.

Your carrier bills you for all these outbound calls; the destination carrier shares part of that revenue with the fraudster . So their direct financial incentive is the outbound spend you incur.

Fraudulent calls can exhaust your monthly budget in a single day. When that happens, Retell pauses calls and API requests when spending reaches 100% of the monthly budget, even if credits remain or auto recharge is enabled.

This stops attackers from continuing to generate calls through your Retell agents after the cutoff, helping prevent further losses until usage resumes.

Retell uses usage-based pricing and offers two plans: ‘pay-as-you-go’ and ‘Enterprise’.

Retell charges you per minute, per message and monthly fees depending on the feature(s) you use. There is also an additional cost associated with API calls made to external systems (like n8n, GHL etc) which may or may not reflect in Retell Invoices.