Understanding biodiversity net gain

Guidance on what BNG is and how it affects land managers, developers and local planning authorities.

Applies to England

Biodiversity net gain (BNG) is mandatory from 12 February 2024.

You can view all of the BNG guidance in the BNG collection.

What BNG is 

BNG is an approach to development. It makes sure that habitats for wildlife are left in a measurably better state than they were before the development.

In England, BNG is 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 BNG 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 value 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. 

Measuring biodiversity value

When considering biodiversity value, you should consult an ecologist. They will:  

  • measure the biodiversity value of your existing habitat  
  • advise on suitable habitat creation or enhancement for the land

Read guidance on using the biodiversity metric.  

Calculating the units

There is a statutory (official) biodiversity metric, which you must use to measure how many units:

  • a habitat contains before development  
  • are needed to replace the units of habitat lost and to achieve 10% BNG

Using the statutory biodiversity metric tool

To calculate 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 biodiversity metric.

Who BNG rules affect 

You need to know about the new rules if you’re a: 

  • developer of major developments 
  • developer of small sites from 2 April 2024    
  • developer of 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 requirements. 

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 at least 10% BNG, as measured by the statutory biodiversity metric.

There are 3 ways a developer can achieve BNG

  1. They can create biodiversity on-site (within the red line boundary of a development site). 
  2. If developers cannot achieve all 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.
  3. If developers cannot achieve on-site or off-site BNG, they must buy statutory biodiversity credits from the government. This should 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


A developer cuts down some trees on the site. They must make up for this impact on the habitat, as well as delivering 10% BNG.

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.  

You must maintain the habitats you create or enhance for a minimum of 30 years. This applies to off-site gains or significant on-site gains.  

Creating, enhancing and maintaining habitats to deliver BNG 

The land owner is legally responsible for creating or enhancing habitat, and managing that habitat for at least 30 years to achieve the target condition. This applies if you make on-site gains or sell off-site gains on a site you own. 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 in England are required to provide 10% BNG on all habitats within the redline boundary of their development, whether or not they are impacted. Separate arrangements apply to on-site irreplaceable habitat.

You must try to avoid loss of habitat when doing development work. Developers must deliver at least 10% BNG, either on-site or off-site, or as a last resort by buying statutory biodiversity credits.  

You should check if the LPA requires you to deliver more BNG.

For off-site gains and significant on-site gains, you must maintain the habitats you create or enhance for a minimum of 30 years. The responsibilities will be set out in a legal agreement

The following guides will help you: 

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 metric tool.

If you have a small development, 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 provide information about how you intend to meet the BNG objective, including details of proposed significant on-site enhancements.  

Find out what information you need to submit with your planning application.

You may need a legal agreement. The terms of the agreement will set out responsibilities for creating, enhancing, monitoring and reporting.  You might also need a habitat management and monitoring plan (HMMP).

If the LPA grants planning permission, you will need to create a biodiversity gain plan that shows how you will achieve BNG. You must provide evidence for some of your BNG decisions.

You must submit your biodiversity gain plan, including a metric tool calculation that shows how you will meet your mandatory BNG, to the LPA. The LPA must approve or refuse your biodiversity gain plan within 8 weeks.  

The LPA must approve your biodiversity gain plan before you can start development. 

You must manage and maintain for 30 years, starting from when you complete the development. This includes when you complete creating or enhancing any on-site habitat (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. 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

You will need to sign a legal agreement with a responsible body or local authority. The legal agreement will set out how you will create, enhance, maintain and monitor the biodiversity of your registered units to deliver off-site biodiversity net gain.  It must last for a minimum of 30 years.

When you sell your units, you (or the developer, with your permission) need to apply to record the allocation of off-site biodiversity gains to a development.

Before you apply to record the allocation of units, you need to register your land as a biodiversity gain site on the national biodiversity gain sites register.

What LPAs have to do

Read guidance for LPAs

Further information  

You can get support from:


Give feedback on this guidance by completing a short survey.

Published 21 February 2023
Last updated 22 February 2024 + show all updates
  1. Updated to clarify that unless exempt, developers in England are required to provide 10% BNG on all habitats within the redline boundary of their development, whether or not they are impacted, and that separate arrangements apply to on-site irreplaceable habitat.

  2. Updated box at top of page to state that biodiversity net gain (BNG) is mandatory from 12 February 2024 and removed the 'draft guidance' label. Updates to measuring biodiversity value and legal agreement information.

  3. Removed links to draft statutory instruments as the final versions have been laid before parliament.

  4. 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.

  5. 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.

  6. Added a link to a feedback survey.

  7. First published.