---
title: interpolate() | Tiger Data Docs
description: Fill in missing values by linear interpolation
---

Since [1.1.1](https://github.com/timescale/timescaledb/releases/tag/1.1.1)

Fill in missing values by linear interpolation. Use in the same query as [`time_bucket_gapfill`](/docs/reference/timescaledb/hyperfunctions/time_bucket_gapfill/time_bucket_gapfill/index.md). `interpolate` cannot be nested inside another function call.

## Arguments

The syntax is:

```
SELECT interpolate(
    value = <anyelement>,
    prev = <anyelement>,
    next = <anyelement>
);
```

| Name    | Type       | Default | Required | Description                                                                                                                                                                                                                                                                                                    |
| ------- | ---------- | ------- | -------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `value` | SMALLINT   | INTEGER | BIGINT   | REAL                                                                                                                                                                                                                                                                                                           |
| `prev`  | EXPRESSION | -       | -        | If no previous value is available for gapfilling, use the `prev` lookup expression to get a previous value. For example, you can use `prev` to fill in the first bucket in a queried time range. The expression must return a `(time, value)` tuple with types corresponding to the bucketed times and values. |
| `next`  | EXPRESSION | -       | -        | If no next value is available for gapfilling, use the `next` lookup expression to get a next value. For example, you can use `next` to fill in the last bucket in a queried time range. The expression must return a `(time, value)` tuple with types corresponding to the bucketed times and values.          |

## Returns

| Column        | Type                                                 | Description                                                          |
| ------------- | ---------------------------------------------------- | -------------------------------------------------------------------- |
| `interpolate` | SMALLINT, INTEGER, BIGINT, REAL, or DOUBLE PRECISION | The gapfilled value. The return type matches the input `value` type. |