# NQL time\_elapsed()
The `time_elapsed()` function calculates the time elapsed since an event. The function returns the values in seconds.
Use this function with a field of *datetime* [data type](/platform/understanding-key-data-platform-concepts/nexthink-query-language-nql/nql-syntax-overview/nql-data-types.md), for example:
* the `last_seen` field from the `devices` table
* `time` from the `device_performance.boots` table
The timeframe specified in your query does not restrict the values returned by the `time_elapsed()` function. For example, the following query retrieves only devices active in the past day, but the values returned by `time_elapsed()` may extend beyond that timeframe.
### Using with the ‘where’ clause
Use the `time_elapsed()` function in a `where` clause.
**Example:**
Retrieve the list of devices where the last operating system update was more than 15 days ago.
{% code overflow="wrap" lineNumbers="true" %}
```
devices
| where operating_system.last_update.time_elapsed() > 15d
```
{% endcode %}
### Using with the ‘list’ clause
Use the `time_elapsed()` function in a `list` clause.
**Example:**
List devices and the time elapsed from their last startup.
{% code overflow="wrap" lineNumbers="true" %}
```
devices
| include device_performance.boots
| where type == fast_startup
| compute last_fast_startup_time = time.last()
| list name, last_fast_startup_time.time_elapsed()
```
{% endcode %}
| Name | Last fast startup time → time elapsed |
| --------------- | ------------------------------------- |
| device-10d267d2 | 1w 0d 1h 8min 22s 0ms |
| device-d1d5abc9 | 17h 38min 22s 0ms |
| device-5117c4c3 | 3w 1d 10h 33min 8s 0ms |
| device-16834449 | 57min 18s 0ms |
| … | … |
### Using with the ‘compute’ clause
Use the `time_elapsed()` function in a `compute` clause.
**Example:**
List devices and the time elapsed from their last startup. Applying chaining of functions (call multiple functions on the same field).
{% code overflow="wrap" lineNumbers="true" %}
```
devices
| include device_performance.boots
| where type == fast_startup
| compute time_since_last_fast_startup = time.last().time_elapsed()
```
{% endcode %}
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