# getUtcAgo

:::caution[Unreleased]
Not in `@northguild/gmt` 1.20.0 on npm yet. It is on `main` and ships in the next release.
:::

## Signature

```ts
getUtcAgo(units: Partial<Record<keyof DurationLike, number>>): string
```

Return the UTC instant before now, as an ISO Instant string, counted from the current time.

- Reads the clock once, after `units` is checked.
- `units` is an object of unit amounts, such as `{ days: 90 }`. A duration string returns "". A fractional amount returns "": write `{ hours: 36 }` for a day and a half.
- Lengths are unsigned: a negative amount returns "". `getUtcIn` counts forward.
- `{ days: 0 }` is a valid length and gives now.
- Whole seconds, floored, always `Z`, so every form of one call names the same second. A caller who wants sub-seconds writes `subtractUtc(getUtcNow(), units)`.
- Calendar units count in UTC, so the result does not change with the server's zone, and a missing day clamps to the end of the month, as `subtractUtc` does. For another zone's wall clock, use `getZonedAgo`.
- It feeds `formatHttpDate`. A past `Expires` that deletes a cookie is `formatHttpDate(getUtcAgo({ days: 1 }))`: RFC 6265 §4.1.2 says servers can delete a cookie by sending one with an `Expires` in the past (§3.1).
- Each call reads the clock. To pin the start, use `subtractUtc(getUtcNow(), units)`.
- Examples read the clock at 2027-06-15T12:00:00Z.

## Parameters

| Parameter | Type | Description |
| --- | --- | --- |
| `units` | `Partial<Record<keyof DurationLike, number>>` | unit amounts, such as `{ days: 90 }`; never negative |

## Returns

ISO Instant string in whole seconds, or "" for invalid `units`, a negative amount or a result outside Temporal's range

## Related types

- [`DateTimeDurationUnit`](/gmt/reference/types/DateTimeDurationUnit)

## Examples

```ts
import { getUtcAgo } from "@northguild/gmt/utc/get";

getUtcAgo({ days: 90 }) // "2027-03-17T12:00:00Z" (90 days back)
```

## Source

[utc/get/getUtcAgo.ts](https://github.com/northguild/gmt/blob/main/packages/gmt/src/utc/get/getUtcAgo.ts)