---
title: Biodiversity Net Gain (BNG) Defined in Plain English
description: "A plain-English definition of biodiversity net gain (BNG) in England: the 10% rule, the 30-year commitment, who it applies to and what changed in 2026."
---

[Pixcellence Blog](https://www.pixcellence.co.uk/blog)

# [Biodiversity Net Gain (BNG) Defined in Plain English](https://www.pixcellence.co.uk/blog/biodiversity-net-gain-defined)

 Written by [Clwyd Probert](https://www.pixcellence.co.uk/blog/author/clwyd-probert) | 29 Oct 2026, 11:30:00

**Biodiversity net gain (BNG) means leaving wildlife habitat in a measurably better state than it was before a development. In England it is the law: most new development must deliver at least a 10% gain in biodiversity value, measured in biodiversity units with the statutory biodiversity metric and maintained for at least 30 years** ([GOV.UK](https://www.gov.uk/guidance/understanding-biodiversity-net-gain)).

This page gives the short definition. For the full explanation, read our [complete guide to biodiversity net gain](https://www.pixcellence.co.uk/blog/biodiversity-net-gain).

BNG in one sentence

BNG = **10% more biodiversity units** after development than before, delivered **on-site first, then off-site, then through statutory credits**, and secured for **30 years**. It is mandatory in England for most planning applications made since February 2024, with new exemptions for small sites from 6 August 2026.

## The definition, in five parts

1. **Biodiversity** is measured through habitat, not species. Each habitat on a site is scored for its area, distinctiveness, condition and strategic significance.
2. **Net** means the total after development is compared with the total before, including all habitat inside the red line boundary.
3. **Gain** means at least 10% more biodiversity units than the baseline. Local plans can ask for more.
4. **Delivery** follows a hierarchy: avoid harm, improve habitat on-site, use registered off-site land, and buy statutory credits only as a last resort.
5. **Commitment** means the new or improved habitat is legally secured and managed for at least 30 years.

## Where BNG comes from

BNG is required by Schedule 7A of the Town and Country Planning Act 1990, inserted by Schedule 14 of the [Environment Act 2021](https://www.legislation.gov.uk/ukpga/2021/30/schedule/14/enacted). It became mandatory on 12 February 2024 for major development and on 2 April 2024 for small sites. In 2026 the rules were amended: from 6 August 2026, new applications on sites of 0.2 hectares or less are exempt unless they affect priority habitat, and the self-build exemption was removed ([SI 2026/790](https://www.legislation.gov.uk/uksi/2026/790/contents/made)). From 2 November 2026, BNG also applies to nationally significant infrastructure projects ([GOV.UK](https://www.gov.uk/guidance/biodiversity-net-gain-nationally-significant-infrastructure-projects)).

## Go deeper

- [Biodiversity net gain explained](https://www.pixcellence.co.uk/blog/biodiversity-net-gain): the full guide, including the off-site market, credits and the evidence so far.
- [BNG regulations 2026](https://www.pixcellence.co.uk/blog/biodiversity-net-gain-regulations): the legislation, every exemption and how gains are secured.
- [How the BNG metric works](https://www.pixcellence.co.uk/blog/biodiversity-net-gain-metric): the formula, the scores and a worked example.
- [The statutory biodiversity metric: strengths and criticisms](https://www.pixcellence.co.uk/blog/statutory-biodiversity-metric-explained-guide): what the research says.

## Frequently asked questions

### What does biodiversity net gain mean?

Biodiversity net gain means leaving the natural environment in a measurably better state than before a development. In England it is a legal requirement for most new development: a gain of at least 10% in biodiversity units, measured with the statutory biodiversity metric and maintained for at least 30 years.

### Is biodiversity net gain a legal requirement?

Yes, in England. It became mandatory for major development on 12 February 2024 and for small sites on 2 April 2024, under Schedule 7A of the Town and Country Planning Act 1990, inserted by the Environment Act 2021. It applies to nationally significant infrastructure projects from 2 November 2026.

### What is a biodiversity unit?

A biodiversity unit is the standard measure used for BNG. The statutory biodiversity metric calculates units from a habitat's area, distinctiveness, condition and strategic significance. A development must have at least 10% more units after development than before.

### Who is exempt from biodiversity net gain?

Householder applications, permitted development, de minimis development and, for applications made from 6 August 2026, sites of 0.2 hectares or less and temporary development of 5 years or less, unless onsite priority habitat is affected. Self-build homes are no longer exempt for new applications.

Sources: [Environment Act 2021, Schedule 14](https://www.legislation.gov.uk/ukpga/2021/30/schedule/14/enacted); [GOV.UK, Understanding BNG](https://www.gov.uk/guidance/understanding-biodiversity-net-gain); [GOV.UK, exempt developments](https://www.gov.uk/guidance/biodiversity-net-gain-exempt-developments); [SI 2026/790](https://www.legislation.gov.uk/uksi/2026/790/contents/made); [GOV.UK, BNG for NSIPs](https://www.gov.uk/guidance/biodiversity-net-gain-nationally-significant-infrastructure-projects).

[View full post](https://www.pixcellence.co.uk/blog/biodiversity-net-gain-defined)

```json
{
  "@context" : "http://schema.org",
  "@type" : "BlogPosting",
  "author" : {
    "@type" : "Person",
    "name" : "Clwyd Probert"
  },
  "dateModified" : "2026-10-29T11:36:20.643Z",
  "datePublished" : "2026-10-29T11:30:00Z",
  "headline" : "Biodiversity Net Gain Defined: BNG in Plain English (2026)",
  "image" : {
    "@type" : "ImageObject",
    "height" : 675,
    "url" : "https://www.pixcellence.co.uk/hubfs/blog/images/bng-guide-habitat-bank-20261029-20261029-112350.webp",
    "width" : 1200
  },
  "mainEntityOfPage" : "https://www.pixcellence.co.uk/blog/biodiversity-net-gain-defined",
  "publisher" : {
    "@type" : "Organization",
    "logo" : {
      "@type" : "ImageObject",
      "height" : 60,
      "url" : "/hs/hsstatic/content_shared_assets/static-1.4092/img/default-amp-logo.png",
      "width" : 60
    },
    "name" : "Pixcellence Blog"
  }
}
```