> For the complete documentation index, see [llms.txt](https://docs.tryterra.co/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tryterra.co/faq/help-topics/data-api-sdk/data-model-fields-and-units/sleep-duration-shorter-than-window.md).

# Why is sleep duration shorter than the session window?

Sleep state durations are **computed from the hypnogram samples the provider returns**.

When a third-party app writes non-continuous hypnogram samples into the provider, the gaps are not counted as asleep time, so the asleep duration can be much shorter than the overall session window.

The provider's own app may still look correct because it displays the **session window**, rather than the sample-derived durations.