> ## Documentation Index
> Fetch the complete documentation index at: https://docs.retellai.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Make outbound calls
> Make outbound phone calls with Retell agents — bind agents to your numbers, prepare API credentials, and trigger calls programmatically or from the dashboard.
## Overview
Make outbound calls with your Retell agents: bind an agent to a phone number, then trigger calls from the dashboard or the API.
## Prerequisites
* **Phone Number**: A [Retell-managed or imported number](/deploy/purchase-number)
* **Agent**: A configured agent ready for outbound calls
* **API Key**: Your Retell API key for authentication
## Step 1: Bind agents to phone numbers
Before making calls, assign agents to your phone numbers. This configuration determines how your number handles both inbound and outbound calls.
### Configuration options
| Setting | Purpose | Use case |
| ------------------ | --------------------------------------- | ----------------------------- |
| **Inbound Agent** | Handles incoming calls to this number | Customer support, callbacks |
| **Outbound Agent** | Used when making calls from this number | Sales outreach, notifications |
### Flexible agent assignment
* **Different agents**: Use specialized agents for inbound vs outbound
* **Outbound only**: Leave inbound agent unset to prevent callbacks
* **Inbound only**: Configure only inbound agent for receive-only numbers
After binding an inbound agent, your number is immediately ready to receive calls. Test it by calling the number!
### A/B testing
See [A/B Testing](/deploy/ab-testing).
## Step 2: Make outbound calls
### International calling restrictions
**Retell-purchased numbers**: Retell supports calling to [15 countries](/deploy/international-call).
**Imported numbers**: International calling depends on your telephony provider's settings.
### Call parameters
When making outbound calls (v2), these parameters are supported:
| Parameter | Type | Example | Description |
| ------------------------------ | -------------- | ------------------------------- | ------------------------------------------------------------------------------------------- |
| `from_number` | string (E.164) | `+14157774444` | Your Retell-managed or imported number. |
| `to_number` | string (E.164) | `+12137774445` | Destination number. |
| `override_agent_id` | string | `agent_abc123` | Override the agent used for this call (optional). |
| `override_agent_version` | integer | `1` | Version of the override agent; defaults to latest if omitted. |
| `agent_override` | object | See below | Per-call partial overrides for agent/response engine (optional). |
| `metadata` | object | `{ "customer_id": "cust_123" }` | Free-form metadata stored with the call (size limit applies). |
| `retell_llm_dynamic_variables` | object | `{ "name": "John" }` | Key–value strings injected into prompts/tools (optional). |
| `custom_sip_headers` | object | `{ "X-Call-ID": "123" }` | Outbound [SIP headers](/build/telephony/sip-headers) forwarded to your provider (optional). |
| `ignore_e164_validation` | boolean | `false` | Only for custom telephony. Bypass E.164 validation for special routing. |
Agent overrides let you adjust per-call behavior without changing the saved agent. See “Agent Overrides” in the [Create Phone Call API](/api-references/create-phone-call) for supported fields and examples.
### API implementation
For complete parameter documentation, see [Create Phone Call API Reference](/api-references/create-phone-call).
```typescript Node theme={"dark"}
const registerCallResponse = await retell.call.createPhoneCall({
from_number: '+14157774444', // replace with the number you purchased
to_number: '+12137774445', // replace with the number you want to call
// Optional: per-call agent selection and overrides
override_agent_id: 'agent_abc123',
override_agent_version: 0, // or omit to use latest
agent_override: {
agent: {
voice_speed: 1.1,
enable_backchannel: true,
},
// retell_llm or conversation_flow overrides are also supported
},
retell_llm_dynamic_variables: { // dynamic variables (optional, string values only)
name: 'John Doe',
blood_group: 'B+'
},
custom_sip_headers: { // replace with custom sip headers you want to send (optional)
'X-Custom-Header': 'Custom Value'
}
});
console.log(registerCallResponse);
```
```python Python theme={"dark"}
# Initiate an outbound call using the newly created agent
call = client.call.create_phone_call(
from_number="+14157774444", # replace with the number you purchased
to_number="+12137774445", # replace with the number you want to call
# Optional: per-call agent selection and overrides
override_agent_id="agent_abc123",
override_agent_version=0, # or omit to use latest
agent_override={
"agent": {
"voice_speed": 1.1,
"enable_backchannel": True,
}
},
retell_llm_dynamic_variables={ # dynamic variables (optional, string values only)
"name": "John Doe",
"blood_group": "B+"
},
custom_sip_headers={ # replace with custom sip headers you want to send (optional)
"X-Custom-Header": "Custom Value"
}
)
print(call)
```
## Step 3: Configure CPS (calls per second)
### Understanding CPS limits
CPS (calls per second) controls how many outbound calls you can start each second.
### Default limits and scaling
| Provider | Default CPS | Maximum CPS | Notes |
| -------------------- | ----------- | ----------- | ---------------------------------------------------------------------------- |
| **Twilio** | 1 | 5 | Changes take up to 10 minutes |
| **Telnyx** | 1 | 16 | Instant updates |
| **Custom Telephony** | 1 | 150 | Check your custom provider's SIP trunk capacity before increasing this limit |
### Important considerations
1. **Throttling protection**: Exceeding limits results in rejected calls
2. **Gradual scaling**: Start low and increase based on actual needs
3. **Provider limits**: Your telephony provider may have additional restrictions
4. **Cost impact**: Higher CPS may increase telephony costs
5. **Concurrency**: CPS controls how fast calls start; the number that can run at once is capped separately by your [concurrency limit](/deploy/concurrency)
### Best practices for high-volume calling
**Implement retry logic** with exponential backoff to handle throttling gracefully:
```javascript theme={"dark"}
// Example retry logic
const maxRetries = 3;
let retryDelay = 1000; // Start with 1 second
for (let i = 0; i < maxRetries; i++) {
try {
await makeCall();
break;
} catch (error) {
if (error.code === 'rate_limited') {
await sleep(retryDelay);
retryDelay *= 2; // Exponential backoff
}
}
}
```
## Step 4: Monitor call details
### Available monitoring methods
#### 1. API polling
Use [Get Call API](/api-references/get-call) to retrieve:
* Full transcript
* Call recording
* Latency metrics
* Function call logs
* Call duration and status
#### 2. Real-time webhooks
Set up [webhooks](/features/webhook-overview#event-types) to receive instant notifications for:
* **Call Started**: When the call connects
* **Call Ended**: Final status and duration
* **Call Analyzed**: Transcript and analysis ready
* **Call Failed**: Error details and reasons
Webhooks provide real-time updates without polling, making them ideal for production systems.
Triggering outbound calls (using Make.com)
### Additional resources
* [Community Templates](https://docs.google.com/document/d/1hx6hdTEjAR4y4xXZ7RLMH2byQNVW1ABxC8S4FwvTx_Y/edit?tab=t.0#heading=h.wf5bktkelope): Real-world outbound calling examples
* [Batch calling](/deploy/make-batch-call): For high-volume campaigns
* [Handle voicemail and IVR](/build/handle-voicemail): Detect voicemail or IVR menus on outbound calls
* [Capture DTMF input](/build/user-dtmf): Collect keypad digits from the caller
* [Debug outbound calls](/reliability/debug-outbound-call): Troubleshoot connection issues
* [Webhook setup](/features/webhook-overview): Configure real-time notifications
### API implementation
For complete parameter documentation, see [Create Phone Call API Reference](/api-references/create-phone-call).