> ## 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.
# Check actual latency
> Monitor per-call latency in the Retell Call History dashboard or via the Get Call API — review P50, P90, and P99 end-to-end latency to find slow calls.
You can monitor the latency of individual calls in [Call History](/features/session-history).
### Understanding latency metrics
End-to-end latency measures the total time from when the user stops speaking until the AI agent begins responding. This includes processing time, network delays, and model inference time.
### Key metrics explained
* **P90 (90th Percentile)**: 90% of calls have latency below this value.
* **Median (50th Percentile)**: Half of the calls have latency less than this value.
* **Min**: The fastest response time achieved in any call.
## Retrieve latency via the API
You can also retrieve detailed latency breakdowns programmatically using the [Get Call API](/api-references/get-call). After a call ends, the response includes a `latency` object with per-component metrics.
```bash cURL theme={"dark"}
curl -X GET "https://api.retellai.com/v2/get-call/CALL_ID" \
-H "Authorization: Bearer YOUR_API_KEY"
```
```python Python theme={"dark"}
from retell import Retell
client = Retell(api_key="YOUR_API_KEY")
call = client.call.retrieve("CALL_ID")
print(call.latency)
```
```javascript Node.js theme={"dark"}
import Retell from "retell-ai";
const client = new Retell({ apiKey: "YOUR_API_KEY" });
const call = await client.call.retrieve("CALL_ID");
console.log(call.latency);
```
### Latency breakdown fields
The `latency` object contains the following components. Not all fields are present on every call — availability depends on the call type and features used.
| Field | Description |
| --------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `e2e` | End-to-end latency from when the user stops talking to when the agent starts talking. Only turns where the agent speaks are counted — turns where the agent just runs tool calls without saying anything are excluded, so tool execution time doesn't inflate this metric. Does not account for network trip time from the Retell server to the user's frontend. |
| `asr` | Transcription latency — the difference between the duration of audio chunks streamed and the duration of the transcribed portion. |
| `llm` | LLM latency from the start of the LLM call to the first speakable chunk received. When using a custom LLM, this includes the websocket roundtrip time. |
| `llm_websocket_network_rtt` | Websocket roundtrip latency between your server and the Retell server. Only populated for calls using a [custom LLM](/integrate-llm/overview). |
| `tts` | Text-to-speech latency from triggering TTS to the first audio byte received. |
| `knowledge_base` | Knowledge base retrieval latency from triggering retrieval to receiving all relevant context. Only populated when the agent uses the knowledge base feature. |
| `s2s` | Speech-to-speech latency from requesting a response to the first byte received. Only populated for calls using a speech-to-speech model (e.g., Realtime API). |
Each component is an object with these statistical fields:
| Field | Type | Description |
| -------- | --------- | -------------------------------------------------- |
| `p50` | number | 50th percentile (median) latency in milliseconds |
| `p90` | number | 90th percentile latency in milliseconds |
| `p95` | number | 95th percentile latency in milliseconds |
| `p99` | number | 99th percentile latency in milliseconds |
| `min` | number | Minimum latency in milliseconds |
| `max` | number | Maximum latency in milliseconds |
| `num` | number | Number of data points tracked |
| `values` | number\[] | All individual latency data points in milliseconds |
### Example response
Here is an example of the `latency` portion of a Get Call response:
```json theme={"dark"}
{
"latency": {
"e2e": {
"p50": 800,
"p90": 1200,
"p95": 1500,
"p99": 2500,
"min": 500,
"max": 2700,
"num": 10,
"values": [500, 620, 780, 800, 850, 900, 1100, 1200, 1500, 2700]
},
"llm": {
"p50": 400,
"p90": 650,
"p95": 800,
"p99": 1200,
"min": 250,
"max": 1300,
"num": 10,
"values": [250, 310, 380, 400, 420, 500, 600, 650, 800, 1300]
},
"tts": {
"p50": 150,
"p90": 250,
"p95": 300,
"p99": 400,
"min": 80,
"max": 420,
"num": 10,
"values": [80, 100, 130, 150, 160, 200, 230, 250, 300, 420]
}
}
}
```