Biodiversity Net Gain Hub

England · Planning · Independent guidance

Biodiversity net gain

Biodiversity net gain (BNG) is England's planning requirement that development leaves biodiversity in a measurably better state than before, with at least a 10% increase in biodiversity units calculated using the statutory biodiversity metric. Biodiversity Net Gain Hub explains the regime in plain English, offers a non-statutory estimator, and cites dated GOV.UK and Natural England guidance. It is educational only, not a statutory calculation and not endorsed by Natural England.

Try the non-statutory estimator Check the exemptions
10%minimum net gain in biodiversity units (England)
30 yearshabitat management secured by legal agreement
12 Feb 2024mandatory for major development; 2 Apr 2024 for small sites
0.2 hasite-size exemption threshold from 6 August 2026

What biodiversity net gain means in England

In England, biodiversity net gain is a statutory condition attached to most grants of planning permission. Schedule 7A of the Town and Country Planning Act 1990, inserted by the Environment Act 2021, requires the development to deliver a "biodiversity gain objective": a post-development biodiversity value at least 10% higher than the pre-development value of the on-site habitat. Value is measured in biodiversity units using Defra's statutory biodiversity metric, and the gain can be delivered on-site, through registered off-site units, or as a last resort through statutory biodiversity credits bought from government.

The condition is pre-commencement: once permission is granted, a biodiversity gain plan (including the metric calculation) must be approved by the local planning authority before work starts. The authority has 8 weeks to decide. Significant on-site and all off-site habitat must then be managed for at least 30 years under a planning obligation or conservation covenant.

Who biodiversity net gain applies to

Who BNG affects and from when (GOV.UK, updated 14 July 2026)
GroupApplies fromWhat it means in practice
Developers of major development12 February 2024Baseline metric with the application; gain plan approved before commencement; 10% gain on all habitat inside the red line.
Developers of small ("minor") sites2 April 2024Same duty; may use the small sites metric if eligible; from 6 August 2026 may consider on-site and off-site at the same time.
Nationally significant infrastructure projects2 November 2026Separate rules under the Planning Act 2008 and biodiversity gain statements.
Land managersOptionalCan register a biodiversity gain site and sell off-site units under a 30-year legal agreement.
Local planning authorities12 February 2024Validate exemption claims, approve gain plans within 8 weeks, monitor and enforce.

Householder applications, permitted development and several other categories are exempt. The bng exemptions page lists them with the dates each came into force.

How the metric and biodiversity units work

The statutory biodiversity metric scores every habitat parcel inside the development boundary. For area habitats, units equal area in hectares multiplied by distinctiveness (very low 0 to very high 8), condition (poor 1 to good 3) and strategic significance (1.0 to 1.15). Habitat that will be created or enhanced is also discounted for the difficulty of creating it and for every year it takes to reach target condition. Hedgerows and watercourses use separate linear units. The baseline total multiplied by 1.10 is the target the post-development total must reach.

Read how the bng metric is calculated, then how bng units, off-site units and statutory credits differ.

Estimate your position before you instruct an ecologist

Our biodiversity net gain calculator is a non-statutory estimator (version 1.0, 17 September 2026). Enter your habitat parcels and planned outcome to see an indicative baseline, the 10% target, any shortfall and what statutory credits might cost at published prices. Every assumption is printed on the page, the worked example is reproducible by hand, and the limitations are explicit. It exists to help you ask better questions of your ecologist and local planning authority, not to replace either.

Exemptions in one paragraph

BNG does not apply to householder development, permitted development, sites of 0.2 hectares or below (applications made on or after 6 August 2026, no priority habitat impacted), temporary development permitted for 5 years or less (same date and priority-habitat test), development impacting under 25 square metres of habitat and under 5 metres of hedgerow (de minimis), biodiversity gain sites, urgent Crown development, and the high-speed rail network. Applications made before 12 February 2024 (or before 2 April 2024 for small sites) are outside the regime, and the self-build exemption closed to new applications on 6 August 2026. Details, evidence tips and FAQs: bng exemptions.

Find a habitat bank, broker or ecologist

The BNG directory lists habitat banks, biodiversity unit brokers, consultant ecologists and planning lawyers across England. Biodiversity Net Gain Hub publishes listings and passes on enquiries; it does not sell or broker biodiversity units or statutory credits, and it is not a party to any unit transaction. For the official list of registered gain sites, use the biodiversity gain sites register on GOV.UK.

Frequently asked questions

What is biodiversity net gain?

Biodiversity net gain (BNG) is the requirement in England that development leaves habitats measurably better than before. Under Schedule 7A of the Town and Country Planning Act 1990, most planning permissions are granted subject to a condition that the development delivers at least a 10% increase in biodiversity value, measured in biodiversity units with the statutory biodiversity metric.

Is 10% biodiversity net gain mandatory?

Yes, in England. The 10% gain has been mandatory for major development since 12 February 2024 and for small ("minor") development since 2 April 2024, unless the development is exempt. It applies to nationally significant infrastructure projects from 2 November 2026. Local plans can only require more than 10% where the policy is evidenced and justified.

What are the new rules for biodiversity net gain in 2026?

From 6 August 2026, developments on sites of 0.2 hectares or below and temporary developments permitted for 5 years or less are exempt from BNG where no priority habitat is impacted; the self-build and custom-build exemption ended for applications made on or after that date; and small developments may consider on-site and off-site delivery at the same time. BNG extends to nationally significant infrastructure projects from 2 November 2026.

What are biodiversity units?

Biodiversity units are the standard measure of biodiversity value used for BNG. The statutory biodiversity metric multiplies a habitat parcel's area by scores for its distinctiveness, condition and strategic significance to produce units; created or enhanced habitat is further discounted for difficulty and the time it takes to reach target condition. Hedgerows and watercourses have their own linear units.

What is the BNG metric?

The BNG metric is Defra's statutory biodiversity metric: a formula and spreadsheet-style calculation tool that converts habitat information into biodiversity units for the baseline (pre-development) and post-development states. It must be used for mandatory BNG; earlier Natural England versions (4.0 and before) are not accepted. A simplified small sites metric exists for qualifying small developments.

Which developments are exempt from BNG?

Exempt categories include householder applications (extensions, loft conversions), permitted development, sites of 0.2 hectares or below and temporary development of 5 years or less (both from 6 August 2026 and only where no priority habitat is impacted), the de minimis rule for impacts under 25 square metres of habitat or 5 metres of hedgerow, biodiversity gain sites themselves, urgent Crown development and the high-speed rail network. Check the live GOV.UK exemptions page and confirm with your local planning authority.

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.