Understanding biodiversity net gain
Guidance on what biodiversity net gain is and how it affects land managers, developers, and local planning authorities.
Applies to England
This draft guidance explains what will apply when BNG becomes mandatory. The guidance will continue to be updated.
What biodiversity net gain is
Biodiversity net gain (BNG) is a way of creating and improving natural habitats. BNG makes sure development has a measurably positive impact (‘net gain’) on biodiversity, compared to what was there before development.
In England, biodiversity net gain (BNG) is becoming mandatory under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021).
Developers must deliver a biodiversity net gain of 10%. This means a development will result in more or better quality natural habitat than there was before development.
Find out more about BNG in:
Measuring biodiversity
For the purposes of BNG, biodiversity is measured in standardised biodiversity units.
A habitat will contain a number of biodiversity units, depending on things like its:
- size
- quality
- location
- type
Biodiversity units can be lost through development or generated through work to create and enhance habitats.
Calculating the units
There is a formulastatutory that(official) calculates: biodiversity metric, which is a way of measuring:
- how many units a habitat contains before development
- how many units are needed to replace the units of habitat lost and to achieve 10% BNG
This formula is called the statutory biodiversity metric.
Using the statutory biodiversity metric tool
To prove you have accurately calculated the number of biodiversity units for existing habitat, or habitat enhancements to achieve BNG, you must use the calculator called the statutory biodiversity metric tool.
This tool applies the statutory biodiversity metric formula.
Read guidance on the standard biodiversity metric.
Who BNG rules will affect
You need to know about the new rules if you’re a:
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developer of:
- major developments when BNG becomes mandatory
- small sites from April 2024
- nationally significant infrastructure projects from late November 2025
- land manager wanting to sell in the BNG market
- local planning authority (LPA)
Exempt developments
Some developments are exempt from BNG regulations.
Find out what types of development are exempt.
Ways to achieve BNG: on-site units, off-site units and statutory biodiversity credits
Through site selection and layout, developers should avoid or reduce any negative impact on biodiversity. They must deliver 10% BNG, as measured by the statutory biodiversity metric.
There are 3 ways a developer can achieve 10% BNG:
- They can enhance and restore biodiversity on-site (within the red line boundary of a development site).
- If developers can only achieve part of their BNG on-site, they can deliver through a mixture of on-site and off-site. Developers can either make off-site biodiversity gains on their own land outside the development site, or buy off-site biodiversity units on the market.
- If developers cannot achieve on-site or off-site BNG, they must buy statutory biodiversity credits from the government. This must be a last resort. The government will use the revenue to invest in habitat creation in England.
Developers can combine all 3 options, but must follow the steps in order. This order of steps is called the biodiversity gain hierarchy. hierarchy.
Example
A developer cuts down some trees on the site. They must make up for this impact on the habitat, as well as delivering a 10% BNG uplift.
They must do a survey of habitat before development and use the statutory biodiversity metric to explore options. This tells them how to make up for the loss of the trees and what more they need to do to achieve 10% BNG.
If they cannot achieve the 10% BNG by creating and enhancing on-site habitats, they must buy off-site units.
If that is not enough to achieve BNG, they must buy statutory biodiversity credits.
The 10% uplift is required whether or not the development impacts existing biodiversity.
Your net gain must be maintained for a minimum of 30 years if you are making off-site gains, or significant on-site gains.
Creating, enhancing and maintaining habitats to deliver BNG
The land manager is legally responsible for creating or enhancing habitat, and managing that habitat for at least 30 years to achieve the target condition.
If you make on-site gains or sell off-site gains on a site you own, you are the land manager. If you buy off-site units, you are paying the land manager to manage the land for 30 years to achieve the target condition.
What developers have to do
There is step by step guidance for developers.
Unless exempt, developers of major developments in England are required to provide 10% BNG once it becomes mandatory.
You must try to avoid loss of biodiverse habitat when doing development work. Developers must deliver 10% biodiversity net gain, either on-site or off-site, or as a last resort by buying statutory biodiversity credits.
For significant on-site gains, and all off-site gains, the BNG must be maintained for at least 30 years. Responsibilities will be set out in a legal agreement.
The following guides will help you:
- when you buy off-site units, record the allocation of off-site biodiversity gains on the public biodiversity gain sites register, with the land manager’s permission
- estimate the cost of and buy statutory biodiversity credits if you’re unable to use on-site or off-site units
Exploring options and using the biodiversity metric
Read guidance on your options and how to find registered off-site units to buy.
You should discuss your plans with an ecologist, who will measure the biodiversity value of your existing habitat and explore ways to achieve BNG using the statutory biodiversity metric tool.
Read guidance on the statutory biodiversity metric.
If you have a small site, you don’t need an ecologist. You can either use the simpler small sites biodiversity metric tool yourself, or someone familiar with the site can do a survey and make a calculation. This could be the project manager, a gardener or a landscape architect.
Read guidance on the biodiversity metric.
Planning permission and biodiversity gain plans
When you apply to the LPA for planning permission, you will need to confirm whether your development is exempt from BNG.
If it is not exempt, you will need to attach a baseline metric tool calculation showing the site’s biodiversity value before development. You should also provide information about how you intend to meet the BNG objective, including details of proposed significant on-site enhancements.
You may need a legal agreement. You may also need a habitat management and monitoring plan (HMMP). The terms of these will set out responsibilities for creation and enhancement, and monitoring and reporting.
If the LPA grants planning permission, you will need to create a biodiversity gain plan. This is a document that shows how you will achieve BNG. In your biodiversity gain plan you must provide evidence for your BNG decisions.
You must submit your biodiversity gain plan, including a biodiversity metric tool calculation that shows how you will meet your mandatory BNG, to the LPA. (See the guidance on the statutory biodiversity metric.) The LPA must approve or refuse your biodiversity gain plan within 8 weeks.
The LPA must approve your biodiversity gain plan before you start development.
If applicable, the 30 years of BNG management and maintenance starts from the time the agreed initial habitat creation or enhancement is completed (for example, after one year of tree planting, pond digging or seeding).
If you do not meet your BNG requirements, you might be in breach of planning conditions, planning obligations or legal agreement, and the LPA could take enforcement action against you.
What land managers have to do
Read step by step guidance for land managers.
‘Land manager’ refers to these different roles across BNG guidance:
- landowner
- farmer
- estate owner
- habitat bank operator
- facilities, property or estate manager
- land agent
- land advisor
- planning authority using land they own
- developer using land they own
Selling on the BNG market is a choice for land managers. It is a potential source of revenue and could fund nature recovery work on your land. You can sell off-site biodiversity units on your land to developers, who may need to buy these under mandatory BNG requirements.
Registering a site and recording units
When you sell your units, you (or the developer, with your permission) need to record the allocation of off-site biodiversity gains to a development.
Before you record the allocation of units, you need to register a biodiversity gain site onto the government’s publicly searchable register of all off-site biodiversity projects.
Measuring biodiversity value
As part of registering, you need to consult an ecologist who will measure the biodiversity value of your existing habitat and advise on suitable habitat creation or enhancement for the land.
Read guidance on using the statutory biodiversity metric tool. .
You will sign a legal agreement with a responsible body or local authority which will set out how you will create, enhance, maintain and monitor the biodiversity of your registered units over a minimum of 30 years, to deliver off-site biodiversity net gain.
What LPAs have to do
Read guidance for LPAs. LPAs.
Further information
You can get support from:
Draft statutory instruments
Draft legislation is available.
The Biodiversity Gain Requirements (Exemptions) Regulations 2024
The Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations 2024
The Biodiversity Gain Site Register Regulations 2024
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Last updated
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Updated the definition of the biodiversity metric, added 'type' to the list of factors the biodiversity metric measures, and added a link to more information about the biodiversity gain hierarchy.
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The guidance has been updated throughout with information and examples about what biodiversity net gain means, how it is measured and how it can be achieved when it becomes mandatory.
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Added a link to a feedback survey.
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First published.