svelte/site/content/tutorial/08-stores/04-derived-stores/text.md

title
Derived stores

You can create a store whose value is based on the value of one or more other stores with derived. Building on our previous example, we can create a store that derives the time the page has been open:

export const elapsed = derived(
	time,
	$time => Math.round(($time - start) / 1000)
);

It's possible to derive a store from multiple inputs, and to explicitly set a value instead of returning it (which is useful for deriving values asynchronously). Consult the API reference for more information.