---
title: extrapolated_delta() | Tiger Data Docs
description: Calculate the extrapolated change from a gauge aggregate
---

Early access [1.6.0](https://github.com/timescale/timescaledb-toolkit/releases/tag/1.6.0)

Calculate the change in a gauge during the time period specified by the bounds in the gauge aggregate. The bounds must be specified for the `extrapolated_delta` function to work. You can provide them as part of the original [`gauge_agg`](/docs/reference/toolkit/counters-and-gauges/gauge_agg/gauge_agg/index.md) call, or by using the [`with_bounds`](/docs/reference/toolkit/counters-and-gauges/gauge_agg/with_bounds/index.md) function on an existing gauge aggregate.

## Samples

Extrapolate the change in a gauge over every 15-minute interval.

```
SELECT
    id,
    bucket,
    extrapolated_delta(
        with_bounds(
            summary,
            toolkit_experimental.time_bucket_range('15 min'::interval, bucket)
        )
    )
FROM (
    SELECT
        id,
        time_bucket('15 min'::interval, ts) AS bucket,
        gauge_agg(ts, val) AS summary
    FROM foo
    GROUP BY id, time_bucket('15 min'::interval, ts)
) t;
```

## Arguments

The syntax is:

```
extrapolated_delta(
    summary GaugeSummary
) RETURNS DOUBLE PRECISION
```

| Name      | Type           | Default | Required | Description                                                                                                             |
| --------- | -------------- | ------- | -------- | ----------------------------------------------------------------------------------------------------------------------- |
| `summary` | `GaugeSummary` | -       | ✔        | A gauge aggregate created using [`gauge_agg`](/docs/reference/toolkit/counters-and-gauges/gauge_agg/gauge_agg/index.md) |

## Returns

| Column              | Type             | Description                                                                       |
| ------------------- | ---------------- | --------------------------------------------------------------------------------- |
| extrapolated\_delta | DOUBLE PRECISION | The extrapolated change in the gauge over the time period of the gauge aggregate. |