# What a maintenance window suppresses

A maintenance window never stops a monitor from checking. What it changes is whether a failing check **alerts**
anyone and whether the downtime **counts** against the monitor's uptime. You choose each one per monitor, with the
**Alerts** and **Stats** tiles in the editor (`suppress.alerts` and `suppress.stats` in the API).

## The two choices

| Tile (API field) | While the window runs | Typical use |
|---|---|---|
| **Alerts** (`suppress.alerts`) | No down notification is sent for the monitor - not by email, SMS, voice, messengers or classic webhook contacts. Escalation steps do not fire. Alerts from the monitor's [attached sub-checks](/monitors/types/attached-sub-checks/) (certificate, domain, blacklist, Web Risk) are held back too. | Every planned change where people should not be paged. |
| **Stats** (`suppress.stats`) | The time is counted as maintenance, not downtime. It is left out of the monitor's uptime percentage, SLA figures and reports. | Planned downtime that should not lower your published uptime. |

Turn on both for a full "this is planned, ignore it"; turn on only **Alerts** when you want to stay quiet but keep
the numbers honest - for example for a dependent service you are not sure will survive the change.

A covered monitor must have at least one of the two on. When you create a window through the API with `monitorIds`
and no `suppress` object, **Alerts** is on and **Stats** is off.

## What still happens

- **Checks run on schedule** from the usual locations, and every result is recorded in the
  [check log](/incidents/reading-results/).
- **Incidents are still recorded.** A down episode that happens during the window is stored like any other, marked
  as under maintenance. The `incident.opened` [webhook event](/reference/webhook-events/) still fires, with
  `underMaintenance: true`, so an integration can tell the two apart.
- **The monitor's state reads `maintenance`.** While its latest check ran inside a window, the API reports the
  monitor's `state` as `maintenance` rather than `up` or `down` (filter with `GET /monitor?state=maintenance`).
- **Monitors outside the window are unaffected**, even when they check the same server.

## Overlapping windows

When several windows cover the same monitor at the same moment, their choices add up: if any active window
suppresses alerts, alerts are suppressed; if any suppresses stats, the time counts as maintenance.

## When the window ends

Suppression stops the moment the window's end time passes:

- A monitor that is **still down** at that moment sends **one** down alert straight away, to the contacts that
  would have been alerted. From then on it follows normal [down detection](/monitors/down-detection/) and
  alerting, including "still down" reminders.
- Downtime after the end counts against uptime again.
- A monitor that recovered during the window sends no recovery alert for an outage nobody was told about.

If the work might run long, extend the window before it ends (change **Ends** or use **Quick add**), or expect that
one alert.

A `maintenance.ended` webhook event fires when a window ends on schedule (`endedEarly: false`) or is cancelled while
active (`endedEarly: true`). Cancelling an active window - deleting it, or turning **Window active** off - makes its
monitors alert again at once.

## How it shows in uptime numbers

With **Stats** on, the covered time is removed from the calculation rather than counted as up or down:

```
uptime % = time up / (time measured - time under maintenance)
```

On a status page, days that contain maintenance for a component are drawn in blue on its uptime bars, but only when
no other component had a real problem that day - blue never hides a real outage. See
[Uptime percentage and SLA](/incidents/uptime-sla/) and
[Show maintenance on your status page](/maintenance/status-page-display/).

## Timing

Changes you make to a window - creating, editing, pausing, cancelling - reach the checking engine within about a
minute. Save a window at least a minute before the work starts.

## Related

- [What a maintenance window is](/maintenance/overview/)
- [Create a maintenance window](/maintenance/create/)
- [How down detection works](/monitors/down-detection/)
- [Uptime percentage and SLA](/incidents/uptime-sla/)