Comply with biodiversity net gain for development in England

Mandatory biodiversity net gain (BNG) has applied to most planning applications in England since February 2024. You must demonstrate that your development leaves biodiversity in a measurably better state than before — a minimum 10% improvement in biodiversity value, maintained for at least 30 years.

BNG is a planning condition, not a voluntary standard. Your local planning authority (LPA) will not discharge the BNG planning condition until you have submitted and agreed a biodiversity gain plan showing how you will achieve and maintain the 10% improvement.

When mandatory BNG applies

BNG is mandatory for:

• Major developments (10 or more dwellings, 1,000 sqm or more of floorspace, or a site of 1 hectare or more) — from 12 February 2024
• Small sites (1 to 9 dwellings, or sites under 1 hectare that are not major) — from 2 April 2024
• Nationally Significant Infrastructure Projects (NSIPs) — for applications submitted on or after 2 November 2026 (enabling provisions in force from 7 May 2026)

Exemptions

BNG does not apply to:

• Householder applications (extensions and alterations to existing dwellings)
• Development on a site of 0.2 hectares or less that does not impact onsite priority habitat, where the planning application was made on or after 6 August 2026
• Self-build or custom-build development of no more than 9 dwellings on a site of 0.5 hectares or less, where the planning application was made before 6 August 2026
• Temporary development with planning permission for no more than 5 years that does not impact onsite priority habitat, where the planning application was made on or after 6 August 2026
• Developments with de minimis habitat impact (under 25 square metres of habitat and under 5 metres of linear feature such as hedgerow, where no onsite priority habitat is affected)
• Biodiversity gain sites; urgent Crown or defence development; and high-speed rail (HS2) development
• Development that does not require an application for planning permission

If you believe an exemption applies, you must still submit evidence to your LPA at the time of the planning application. The brownfield exemption was removed — BNG applies to brownfield sites.

Small sites exemption: Since 6 August 2026, new planning applications for development sites of 0.2 hectares or less are exempt, except where onsite priority habitat is affected. Applications made before that date remain subject to the previous rules, including the self-build and custom-build exemption, which does not apply to applications made on or after 6 August 2026.

Commission a baseline habitat survey

Before you can calculate BNG, a qualified ecologist must survey and map all habitats on your site using the UK Habitat Classification (UKHab). The survey must be carried out within 2 years before you submit your planning application. The ecologist will assess the type, condition, and strategic significance of each habitat parcel.

Engage an ecologist early — ideally during pre-application discussions with your LPA. Survey findings can influence site layout to protect high-value habitats and reduce the BNG burden.

Calculate your biodiversity gain plan

Your ecologist uses the statutory biodiversity metric to calculate baseline biodiversity units and post-development biodiversity units. The difference must be at least 10% in your favour. Any version of the statutory metric tool can be used, because updates do not change the unit outputs.

The metric uses three types of biodiversity unit: area habitats, hedgerow units, and watercourse units. You must achieve 10% net gain across each type independently — you cannot use surplus hedgerow units to offset a deficit in area habitats.

Irreplaceable habitat, such as ancient woodland, ancient and veteran trees and blanket bog, is treated differently. It cannot be recreated, so the 10% objective does not work in the usual way: you must minimise the harm and agree a bespoke compensation strategy with your LPA. Planning permission for development that loses irreplaceable habitat is granted only in exceptional circumstances.

Submit your biodiversity gain plan

Your planning permission carries the biodiversity gain condition. You submit the biodiversity gain plan to your LPA after it grants permission, using the GOV.UK template, and you cannot start the development until the LPA approves the plan and your metric calculation. The LPA has 8 weeks to approve or refuse it.

The plan must include:

• your completed metric calculation
• pre-development and post-development plans showing where on-site habitat is, the direction of north and an identified scale
• a compensation plan if the development affects irreplaceable habitat
• biodiversity gain site register reference numbers if you use off-site units
• proof of purchase if you buy statutory credits
• how you will manage and monitor significant on-site gains, for example through a habitat management and monitoring plan

Phased developments need an overall plan and a separate plan for each phase.

Deliver the required biodiversity units

You must deliver BNG following the statutory hierarchy — on-site first, then off-site, with statutory credits only as a last resort. You will need to demonstrate to your LPA why you cannot achieve the full 10% on-site before using off-site units or credits.

If you use off-site units, the habitat bank site must be registered on the Natural England biodiversity gain site register before your LPA discharges the BNG planning condition. You cannot discharge the condition until registration is confirmed. You can also create the gain on other land you control, but that land must itself be registered as a biodiversity gain site, which needs a legal agreement with a responsible body or local authority, before you record the allocation of its units to your development.

Statutory credits are purchased directly from Natural England. They are significantly more expensive than on-site or off-site delivery and are intended to be a last resort — not a convenient shortcut. Revenue from credit sales funds habitat creation elsewhere in England.

Credits are priced in tiers by habitat type, and a spatial risk multiplier means you must buy 2 credits for every biodiversity unit you need. Area habitat credits for higher-distinctiveness habitats cost far more than the lowest tier: the top tier on the price list updated on 2 June 2026 is £650,000 per credit. Natural England reviews the prices every 6 months and gives at least 10 weeks' notice of changes.

Secure 30-year habitat management

Every development subject to BNG must have a habitat management and monitoring plan (HMMP) secured through a planning condition, Section 106 agreement, or conservation covenant. The HMMP legally commits the landowner — and any future owner — to managing and monitoring habitats for at least 30 years.

The management obligation transfers with the land. If you sell the site, the buyer takes on the HMMP obligations. Build the 30-year management cost into your development appraisal: habitat establishment in the first years usually needs the most intensive work, followed by routine management, professional monitoring surveys at each monitoring point, and remedial work if habitats fail to reach their target condition. If you hand management to a company or trust, expect to fund the full 30 years up front. For larger schemes, consider using a specialist habitat management company or transferring management to a local wildlife trust.

What happens if you do not comply

Failure to comply with BNG obligations is a breach of planning condition. Your LPA can issue an enforcement notice requiring you to provide alternative or additional habitat. There is no direct financial penalty fixed by statute, but continued breach can result in injunctions, stop notices, and prosecution in the magistrates' court.