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

Since [1.3.0](https://github.com/timescale/timescaledb-toolkit/releases/tag/1.3.0)

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

## Samples

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

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

## Arguments

The syntax is:

```
extrapolated_delta(
    summary CounterSummary,
    method TEXT
) RETURNS DOUBLE PRECISION
```

| Name      | Type             | Default | Required | Description                                                                                                                             |
| --------- | ---------------- | ------- | -------- | --------------------------------------------------------------------------------------------------------------------------------------- |
| `summary` | `CounterSummary` | -       | ✔        | A counter aggregate created using [`counter_agg`](/docs/reference/toolkit/counters-and-gauges/counter_agg/counter_agg/index.md)         |
| `method`  | `TEXT`           | -       | ✔        | The extrapolation method to use. Not case-sensitive. The only allowed value is `prometheus`, for the Prometheus extrapolation protocol. |

## Returns

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