Biodiversity Net Gain in 2026: What Landowners Need to Know

Biodiversity Net Gain is a legal requirement in England under the Environment Act 2021. It became mandatory for major developments in February 2024 and for smaller sites in April 2024. It applies in England only. Wales, Scotland and Northern Ireland have their own approaches.

An ecologist measures the "biodiversity units" on a site before development, using the government's statutory metric. The development must then deliver at least 10% more units than it removes, and the gain must be secured for at least 30 years. Planning permission comes with a condition that a biodiversity gain plan is approved before work starts.

The statutory metric turns habitats into numbers so they can be compared before and after development. Each area of habitat is scored on:

• Type and distinctiveness. How rare and valuable the habitat is. Intensive arable land and improved grassland score low. Species-rich meadows, old orchards and ancient woodland score high.
• Size. The area of each habitat, or the length for hedgerows and watercourses.
• Condition. How good an example it is, from poor to good.
• Strategic significance. Whether the habitat is in a location identified as important in a local nature recovery strategy.

Hedgerows and rivers are measured separately from area habitats, as linear units, and the 10% gain has to be achieved in each category. A site with long, species-rich hedgerows can find the hedgerow requirement harder than the area requirement.

How the Scores Work

For each area of existing habitat, the metric multiplies the area in hectares by a distinctiveness score, a condition score and a strategic significance multiplier. The result is a number of habitat units.

New habitat is scored the same way, but the metric then reduces it to reflect how long it takes to establish and how difficult it is to create. A wildflower meadow sown next spring does not count as a mature meadow straight away.

Two lessons come out of even a simple example. First, low-value arable land gives a low starting figure, which makes the target easier to hit. Second, the open space in a scheme does most of the work, and a modest amount of extra space or better-quality habitat on site can remove the need to buy units at all.

The same calculation on species-rich grassland in good condition would start several times higher, and the target would be much harder to meet on site. That is the difference between Site A and Site B in the comparison below.

Developers are expected to work through three options, broadly in this order:

1. On-site gain. Creating or improving habitats within the development, such as wildflower grassland, new hedgerows, ponds and drainage swales. Significant on-site gains are secured by a planning obligation or conservation covenant for 30 years.
2. Off-site units. Buying units from land elsewhere that has been improved and registered on the national biodiversity gain site register, run by Natural England.
3. Statutory credits. Buying credits from the government as a last resort. These are deliberately priced higher than the market so that they are used only when there is no other option.

In practice, many housing schemes achieve most of their gain on site, as part of the open space, landscaping and sustainable drainage they need anyway, and buy a smaller number of off-site units to make up the balance.

1. Before the application. An ecologist surveys the land, ideally in the right season, and records the existing habitats. The metric gives the starting number of units, and the layout is designed with the target in mind.
2. With the application. The applicant says whether BNG applies or an exemption is claimed. If it applies, the application includes the pre-development biodiversity value, the completed metric, a plan of existing habitats and details of any significant on-site enhancements.
3. The decision. Planning permission is subject to the general biodiversity gain condition, which applies by law. Significant on-site habitat is usually secured by a planning obligation or conservation covenant.
4. After permission, before work starts. The developer submits a biodiversity gain plan showing how the 10% will be met, including any off-site units. The council must approve or refuse it within 8 weeks, and development cannot start until it is approved.
5. Construction. Habitats are created, and any off-site units are allocated to the development on the national register.
6. The next 30 years. The habitats are managed and monitored under the management plan, with reports to the council.

For a landowner under an option or promotion agreement, the practical points are the survey visits in the first stage and, if the scheme needs off-site units from your retained land, the legal agreement in the third or fourth.

For planning applications submitted on or after 6 August 2026:

• Developments on sites under 0.2 hectares (about half an acre) are exempt, unless they affect priority habitat on site.
• Temporary developments where the land is reinstated within five years are exempt, again unless priority habitat is affected.
• Minor developments that are not exempt can go straight to buying off-site units, rather than having to try on-site gain first.
• The separate exemption for self-build and custom-build homes has been removed, although many such plots will fall under the 0.2 hectare threshold.

Applications submitted before 6 August 2026 continue under the old rules. The government has said further exemptions for some conservation projects and park and playing field schemes will follow later in 2026.

The August 2026 NPPF also says councils should not ask for more than the statutory 10% unless a higher figure is justified for specific strategic sites and set out in their plan. Some councils had adopted local policies asking for 20%. That approach is now much harder to apply to ordinary housing sites.

It Changes the Layout

Space set aside for habitat reduces the area available for homes. On an arable field, which usually scores low for biodiversity, 10% is often achievable within the open space a scheme needs anyway. On species-rich grassland, old orchards or land with mature hedgerows, it can take a large share of the site or require off-site units.

It Changes the Numbers

Every pound a housebuilder spends on BNG is a pound it cannot pay for the land. That is why BNG needs to be understood before a price is agreed, not after. The cost varies enormously: from very little on an intensive arable field to a significant sum on a site with valuable habitats.

It Can Create a Second Opportunity

Land that is unlikely to get planning permission, such as a field in the floodplain, may be suitable as an off-site gain site, earning income from selling biodiversity units to developers. This is a 30-year commitment, secured by a legal agreement, and needs specialist advice, but it is worth knowing about. Some landowners combine the two: part of a holding is put forward for housing, and another part is enhanced to provide the off-site units the scheme needs.

A habitat bank is land that has been improved for nature so that its extra biodiversity units can be sold to developers who cannot meet the 10% on their own sites. To sell units, the landowner needs a baseline survey, a habitat management and monitoring plan, a legal agreement securing the land for at least 30 years (a planning obligation with the council or a conservation covenant with a responsible body) and registration of the site on the biodiversity gain site register, which Natural England runs.

Prices for off-site units are agreed privately between buyer and seller, so there is no official market price. They depend on the type of habitat, how many units are available locally and how much demand there is from development nearby.

The government's statutory credits give a ceiling of sorts. At the time of writing (September 2026), the cheapest tier costs £42,000 per credit, and a developer has to buy two credits for every unit it needs, so at least £84,000 per unit. The price list is reviewed every six months. The government says these prices are not guideline prices for off-site units, and they are deliberately set high so that developers buy from the private market first.

Location matters to buyers. Units from a site in the same council area or National Character Area count in full. Units from a neighbouring area count at 75%, and from further away at 50%. That means a habitat bank close to where homes are being built is worth more to a developer than one far away.

Whether gains are on site or off site, they have to be created and then managed for at least 30 years. That means a habitat management plan, regular monitoring and reporting, and money set aside for the work.

On a housing scheme, on-site habitat is usually managed by a management company funded by the residents, or handed to a council or trust. For an off-site gain site on your own land, the obligations stay with the land for 30 years, even if you sell it. That is why becoming a habitat bank is a significant decision that needs proper legal and ecological advice.

Under our agreements, we commission and pay for the ecology surveys, the metric calculation, the habitat design and any off-site units needed. We design the scheme so that as much of the gain as possible is delivered on site, as part of the open space the new homes need anyway.

You do not pay for any of it, and it does not reduce the price we agree with you. Because we look at ecology during the desktop review, before a price is agreed, BNG is already allowed for in our offer rather than deducted later.

• Keep managing the land as you normally do. There is no need to change anything.
• Do not clear hedges, trees, scrub or grassland in anticipation of a sale.
• Tell us about any ponds, old orchards, wet areas or unusual plants you know of. They affect the design.
• If part of your land is unlikely to be developed, ask whether it could provide off-site units.