---
title: interpolated_uptime() | Tiger Data Docs
description: Get the total time live from a heartbeat aggregate and predecessor
---

Since [1.15.0](https://github.com/timescale/timescaledb-toolkit/releases/tag/1.15.0)

Calculate uptime from a heartbeat aggregate, taking the heartbeat aggregate from the preceding interval to interpolate values at the boundary. This checks when the last heartbeat in the predecessor was received and makes sure that the entire heartbeat interval after that is considered live. This addresses the issue where `uptime` would consider the interval between the start of the interval and the first heartbeat as dead.

## Samples

Given a table called `liveness` containing weekly heartbeat aggregates in column `health` with timestamp column `date`, use this command to get the total interpolated uptime of the system during the week of Jan 9, 2022.

```
SELECT interpolated_uptime(
  health,
  LAG(health) OVER (ORDER BY date)
)
FROM liveness
WHERE date = '01-9-2022 UTC'
```

Returns:

```
interpolated_uptime
-------------------
  6 days 23:56:05
```

## Arguments

The syntax is:

```
interpolated_uptime(
    agg HEARTBEATAGG,
    pred HEARTBEATAGG
) RETURNS INTERVAL
```

| Name | Type         | Default | Required | Description                                                                           |
| ---- | ------------ | ------- | -------- | ------------------------------------------------------------------------------------- |
| agg  | HeartbeatAgg | -       | ✔        | A heartbeat aggregate to get the liveness data from                                   |
| pred | HeartbeatAgg | -       |          | The heartbeat aggregate for the interval before the one being measured, if one exists |

## Returns

| Column               | Type     | Description                                                                                                              |
| -------------------- | -------- | ------------------------------------------------------------------------------------------------------------------------ |
| interpolated\_uptime | INTERVAL | The sum of all the live ranges in the aggregate, including those covered by the last heartbeat of the previous interval. |