What is Biodiversity Net Gain?
Biodiversity net gain (BNG) is a planning requirement that requires any development subject to planning permission to result in a net increase in biodiversity value.
The core goal is to halt and reverse the long-term decline in nature across England. It sits within the government’s broader commitment to environmental improvement, set out in the Environmental Improvement Plan.
The legal foundation is the Environment Act 2021, which made BNG a statutory requirement by inserting Schedule 7A into the Town and Country Planning Act 1990. The National Planning Policy Framework (NPPF) had already set a policy expectation for net gains in biodiversity to be part of planning decisions; the Environment Act put it on a legal footing.
Projects can achieve BNG through three routes: on-site habitat creation or enhancement, off-site biodiversity units, or as a last resort, statutory biodiversity credits purchased from the government. These can be combined, but any combination must be agreed with an ecologist.
Once a developer knows how many units need to be created, they can partner with land managers who have worked to develop the biodiversity value of their land. Any land owner or manager can sell biodiversity units, as long as they meet the requirements. Suppliers of units will be able to work with developers anywhere in the country, provided their use is appropriate for the biodiversity impact of the development. The metric also favours biodiversity nearer the development - so local improvements are worth more.
This is the third and least preferred option, only available once on and off site options have been fully explored. Revenue will be invested by the government in habitat creation. Natural England will run this process and the government’s expectation is that they will be phased out once the market has matured. We expect an indicative credit price to be set 6 months before BNG becomes mandatory.
Finding potential BNG habitats that meet site requirements in the right locations can be challenging.
The Gaia website was useful in setting out options, allowing locations to be filtered by different LPAs, NCAs, and clearly setting out the habitat types available. This was useful in deciding who to approach for quotes.
Andy Reading
Polden Planning
What are Biodiversity Units?
A biodiversity unit is a standardised measure of habitat value. Units are calculated using Natural England’s statutory biodiversity metric, which assesses the size, condition, distinctiveness, and strategic significance of a habitat to produce a numeric score.
When a development disturbs or removes habitat, it loses units. The developer must then generate at least 10% more units than were lost, either on the development site itself, through registered off-site land, or via statutory credits. The units of measurement are called Biodiversity Units (you can buy and sell them on the Gaia marketplace).
The current version is Biodiversity Metric 4.0. Whatever route is used to deliver the gain, the habitat must be secured and managed for a minimum of 30 years.
BNG: Mandatory Since February 2024
Since 12 February 2024, all major development projects in England have been required to demonstrate a minimum 10% increase in biodiversity net gain as a condition of planning permission. The requirement extended to smaller development sites from 2 April 2024. BNG for Nationally Significant Infrastructure Projects (NSIPs) will become mandatory from November 2026. DEFRA confirmed this timeline in April 2026, adjusting the original date to give developers sufficient time to integrate the framework into their scheme designs.
Gigas
What Does Increasing Biodiversity Actually Mean?
There are two main options, we have habitat creation or we have habitat enhancement/ restoration. The first is taking an area and building out biodiversity that never existed before. The second is taking areas that either used to have or still have existing biodiversity and either restoring or adding to the existing habitat setup.
Broad Habitats
Habitat Types
This categorisation is important because the units a developer purchases need to align with the biodiversity that is disrupted. So if hedgerows are being lost through development, developers would need to purchase the necessary amount of hedgerow units. To find out more about what you need to do see our purchasing guide here.
What is the Biodiversity Metric and How Do You Calculate the Value of Biodiversity Units?
The statutory biodiversity metric is the official tool used to calculate how many biodiversity units a site holds before and after development. It is integrated into Gaia. The current version is Biodiversity Metric 4.0.
Use the official BNG metric tool: https://www.gov.uk/government/publications/statutory-biodiversity-metric-tools-and-guides
DEFRA has confirmed it will migrate the metric tools from Excel to a digital integrated service to improve usability, particularly for smaller developers. This transition is expected during 2026 as part of the wider BNG reforms.
There are four main factors that the biodiversity metric assesses and we have broken these down below:
Habitat Size
Habitat Condition
Habitat Distinctiveness
Strategic Significance
Biodiversity Net Gain fosters the restoration and enhancement of habitats plus the creation of new ones. Prolonged development and construction without BNG in place has had a detrimental effect on biodiversity and habitats nationwide. Through BNG, species will thrive, and ecosystems will regain their natural balance.
An integral aspect of BNG is habitat creation, wherein developers are encouraged to create wildlife habitats or improve existing ones.
In off-site biodiversity units where habitat delivery is the focus, groups will be investing into neglected landscapes and across the 30 years, will be creating a diverse, flourishing habitat with additional spaces for flora and fauna, resulting in more robust ecological environments.
By preserving and restoring natural habitats, BNG plays a pivotal role in climate change mitigation and adaptation.
Enforcing biodiversity will effectively sequester carbon emissions and directly contribute to carbon offsetting, plus leave us with more and more resilient ecosystems maintained by sustainable development.
The framework allows the country to combine efforts to counter biodiversity offsets and reap environmental and economical benefits nationwide.
By enforcing sustainable development practices, the biodiversity impact will create opportunities for green jobs while supporting industries that prioritise biodiversity, contributing towards long-term economic stability.
It ensures prolonged nature conservation over 30 years by encouraging habitat banks, maintained and monitored by one party for biodiversity preservation.
It also generates long-term financing for habitat maintenance and management, which creates an array of potential jobs. BNG increases the biodiversity value of areas, overall contributing to more economically viable communities.
Why is BNG so important?
BNG matters because development has historically come at a cost to the natural environment. Decades of construction without robust ecological requirements has degraded habitats, reduced species abundance, and fragmented the green networks that wildlife depends on.
By requiring developers to generate measurable gains, BNG creates diverse wildlife habitats, improves green space, air quality, and water quality, and builds more ecologically resilient communities. DEFRA estimates the regime is set to prevent between 6,000 and 10,000 hectares of habitat loss annually, an area roughly the size of Nottingham.
At a broader level, BNG supports the government’s Local Nature Recovery Strategies and contributes to the legally binding biodiversity targets set under the Environment Act 2021. Combined with measures like regenerative farming and peatland restoration, it forms part of the wider effort to protect the natural environment for future generations.
Key groups affected by Biodiversity Net Gain
BNG is applicable to a broad spectrum of groups across the country, such as land managers, developers, LPAs, ecologists, councils, and construction figures.
Developers will utilise the guidance, plans, and templates provided by the government to navigate how they will undertake sustainable development, and LPAs will crucially assess their BNG Plans and decide to approve these plans in line with climate goals.
Land Managers
Local Planning Authorities (LPAs)
The BNG Process
The BNG process follows a structured sequence tied to the planning application:
- Ecological baseline survey: the existing habitats on the development site are mapped, measured, and scored using the statutory biodiversity metric.
- Development design: the design should minimise habitat loss where possible, in line with the mitigation hierarchy.
- BNG calculation: the metric is used to determine pre-development unit scores and the number of post-development units needed to achieve a 10% net gain.
- Biodiversity Gain Plan: a formal plan is submitted to the LPA setting out how the gain will be delivered, maintained and monitored, and which route (on-site, off-site, credits) is being used.
- LPA approval: the Biodiversity Gain Plan must be approved before development commences.
- 30-year monitoring: habitat delivery is secured via planning condition, Section 106 agreement, or conservation covenant, and is subject to regular monitoring throughout the period.
Statutory biodiversity credits are available as a last resort through Natural England, but only once on-site and off-site options have been fully explored and evidenced.
Biodiversity Net Gain Assessments
When delivering biodiversity net gain, BNG assessments are crucial in determining the effectiveness of biodiversity conservation efforts. These assessments evaluate the ecological impact of development projects, ensuring that the mandated net gain in biodiversity is achieved through comprehensive and sound measures. Assessments are aided by the BNG metric, which calculates the number of biodiversity units of a site and how many are required after development to meet the net objective.
Gigas
Those exempt from BNG
Not all development is subject to mandatory BNG. The full list of exemptions is set out in the Biodiversity Gain Requirements (Exemptions) Regulations 2024.
The main categories are householder applications (extensions, conversions, loft conversions), development carried out to fulfil existing BNG obligations, and high-speed rail infrastructure.
A de minimis exemption covers very small impacts: less than 25 square metres of habitat or less than 5 metres of linear habitat.
From July 2026, subject to parliamentary scheduling, a new area-based exemption for sites of 0.2 hectares or below will replace much of the de minimis approach. Temporary permissions of up to five years will also become exempt, and later in 2026 DEFRA expects to add exemptions for development whose primary purpose is conservation, and for works improving parks, playing fields, and public gardens.
The existing small-scale self-build exemption will be removed at the same time.
What is Changing in BNG in 2026?
Following consultation responses published in April 2026, the government confirmed a package of reforms to how BNG operates. The key changes are:
- NSIPs: BNG becomes mandatory for Nationally Significant Infrastructure Projects from November 2026. The streamlined framework applies only to habitats impacted by the development, not the entire site footprint.
- 2ha exemption: A new area-based exemption for sites of 0.2 hectares or below is due by the end of July 2026, replacing much of the de minimis threshold for smaller sites.
- Minor development: Off-site gains will carry equal weight to on-site delivery in the gain hierarchy for minor developments, giving smaller developers more flexibility.
- Digital metric: The current Excel-based statutory biodiversity metric tools are being migrated to a digital integrated service.
- Open Mosaic Habitat: Updated guidance on identifying OMH and other urban habitats, with a proxy habitat introduced where no OMH units are available.
- Brownfield residential: A consultation on a targeted BNG exemption for brownfield residential development closed in June 2026. Outcomes are pending.
Until any legislative changes take effect, the current BNG requirement continues to apply. Developers should follow existing DEFRA guidance and legislation when delivering BNG.