# Duration

Explore what information is available for durations.

This type represents a period in a particular unit, such as months, days, or seconds.

A duration can be positive or negative, indicating a past or future period, respectively. Like all other time types, durations follow the ISO 8601 standard. This is why they are formatted as [periods](https://en.wikipedia.org/wiki/ISO_8601#durations) when converted to a string.

For more information, refer to the [Duration reference](/reference/cql/expressions/durations).