Definition · England
What is biodiversity net gain?
Biodiversity net gain (BNG) is the legal requirement in England that development leaves habitats for wildlife in a measurably better state than before. Most planning permissions granted for applications made on or after 12 February 2024 carry a condition that the scheme delivers at least a 10% increase in biodiversity units, calculated with Defra's statutory biodiversity metric and secured for at least 30 years.
Definition
GOV.UK defines BNG as "an approach to development" that "makes sure that habitats for wildlife are left in a measurably better state than they were before the development". The legal mechanism is the biodiversity gain condition in Schedule 7A of the Town and Country Planning Act 1990, inserted by Schedule 14 of the Environment Act 2021: every grant of planning permission in England is deemed subject to a condition that the "biodiversity gain objective" is met, unless the development is exempt. The objective is a post-development biodiversity value at least 10% higher than the pre-development value of the on-site habitat.
"Measurably" matters. Value is expressed in biodiversity units produced by the statutory biodiversity metric, so a gain can be checked arithmetically rather than argued qualitatively. See how the bng metric works.
Why biodiversity net gain exists
The Environment Act 2021 introduced mandatory BNG so that development contributes to, rather than erodes, nature recovery. Before 2024, net gain was a policy expectation in the National Planning Policy Framework but not a quantified legal duty; outcomes varied by authority. The statutory framework standardises the measure (one metric), the target (10%), the delivery routes (on-site, registered off-site units, statutory credits) and the duration (30 years), and it makes the gain plan a pre-commencement approval so the promise is checked before ground is broken.
Key terms
| Term | Meaning | Learn more |
|---|---|---|
| Biodiversity unit | The standard measure of habitat value: area × distinctiveness × condition × strategic significance (with extra risk factors for new habitat). | BNG units |
| Statutory biodiversity metric | Defra's formula and calculation tool that must be used for mandatory BNG. | BNG metric |
| Baseline | Pre-development biodiversity value of all on-site habitat inside the red line boundary. | BNG assessment |
| Biodiversity gain hierarchy | On-site gains first, then registered off-site units, then statutory credits as a last resort. | BNG units |
| Biodiversity gain plan | The document, including the metric calculation, that the local planning authority must approve before commencement. | BNG assessment |
| Habitat bank / gain site | Land registered on the national biodiversity gain sites register that sells off-site units under a 30-year agreement. | BNG directory |
| Statutory credit | A last-resort unit bought from government at published prices; 2 credits per unit needed. | BNG units |
| Exempt development | Categories the condition does not apply to, such as householder applications and sites of 0.2 ha or below. | BNG exemptions |
Who has to think about it
- Developers must submit baseline information with the application, deliver the 10% gain and get a gain plan approved before commencement.
- Land managers can register a gain site and sell off-site units, taking on 30-year management obligations.
- Local planning authorities validate exemption claims, approve gain plans within 8 weeks and monitor delivery.
- Householders extending their own homes are generally exempt.
Scotland, Wales and Ireland caveat
The 10% statutory requirement described on this hub applies in England only. Scotland's National Planning Framework 4 requires development to "conserve, restore and enhance biodiversity" and deliver positive effects, implemented through NatureScot guidance rather than a statutory metric. Wales operates under Planning Policy Wales and the Environment (Wales) Act 2016. The Republic of Ireland's planning system is separate again. None of these is "the same as England BNG", and this hub does not publish equivalents for them.
Frequently asked questions
What does BNG stand for?
BNG stands for biodiversity net gain. In England it refers to the statutory requirement, under Schedule 7A of the Town and Country Planning Act 1990, for development to deliver at least a 10% increase in biodiversity value measured in biodiversity units.
When did biodiversity net gain become mandatory?
Biodiversity net gain became mandatory in England on 12 February 2024 for major development and on 2 April 2024 for small ("minor") development, for planning applications made on or after those dates. It becomes mandatory for nationally significant infrastructure projects from 2 November 2026.
How does biodiversity net gain work?
A competent ecologist surveys the habitats inside the development boundary and uses the statutory biodiversity metric to calculate baseline biodiversity units. The developer designs the scheme to retain and create habitat on site, buys registered off-site units for any remaining shortfall, and only as a last resort buys statutory credits. After permission, a biodiversity gain plan must be approved before work starts, and created or enhanced habitat is managed for at least 30 years.
Does biodiversity net gain apply in Scotland, Wales or Ireland?
No, not in the English statutory form. Scotland applies "positive effects for biodiversity" through National Planning Framework 4 and NatureScot guidance; Wales works through its own planning policy and the Environment (Wales) Act 2016; the Republic of Ireland has separate planning and biodiversity law. This hub covers England only and does not treat other frameworks as equivalent.
Sources
Official guidance this page relies on, with the "last updated" date shown on each source when this page was written. Always check the live GOV.UK page before acting.
- Understanding biodiversity net gain — GOV.UK (Defra) (updated 14 July 2026)
- Biodiversity net gain — Planning Practice Guidance (MHCLG) (updated 31 July 2026)
- Biodiversity net gain: guidance for developers, land managers and authorities — GOV.UK (updated 27 August 2026)
- NatureScot — Developing with Nature guidance (Scotland) (updated 2026)