# Calculate the linear interpolation between two numbers

Blend from a to b by an amount between 0 and 1.

Canonical: https://1loc.dev/math/calculate-the-linear-interpolation-between-two-numbers/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function lerp({ a, b, amount }) { return (1 - amount) * a + amount * b; }
```

## Input

```json
{
  "a": 0,
  "b": 100,
  "amount": 0.25
}
```

## Expected output

```json
25
```

## Edge case

Input:
```json
{
  "a": 10,
  "b": 20,
  "amount": 1.5
}
```
Output:
```json
25
```

## Limits

- Amounts outside 0–1 extrapolate, as the edge case shows; clamp first when you need to stay in range.

The lab validates types and size before calling this function. Add equivalent validation at your own trust boundary.

## Source and license

Original: https://github.com/phuocng/1loc/blob/14b481cf60dff1620ab1bb99a43b1f68068cdd9b/contents/calculate-the-linear-interpolation-between-two-numbers.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: See original repository history
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Curated implementation; explicit input contract, edge case and limits. Original MDX retained as inert source evidence.