Biodiversity Net Gain Calculator (BNG)
Calculate your mandatory 10% statutory biodiversity uplift, on-site vs off-site habitat unit deficits, and estimate off-site unit and statutory credit costs for planning applications.
Statutory 10% BNG Metric & Deficit Calculator
1 hectare ≈ 2.47 acres
Distinctiveness: Low
Rain gardens, wildflower swales, native hedgerow planting.
10.0% Minimum
1.95
Pre-development2.15
Includes +10% gain1.69
On-site total~£12,880
(Est. £28k/unit)~£38,640
(Natural England Tier A1)Legal Requirement: All BNG habitat enhancements must be formally secured for a minimum 30-year duration through planning conditions, a Section 106 legal agreement, or a conservation covenant.
The 4 Core Statutory Rules of Mandatory UK 10% BNG
Under the Environment Act 2021, every planning permission in England (unless exempt) carries a mandatory pre-commencement condition requiring local planning authority approval of a Biodiversity Gain Plan.
Minor developments (1 to 9 dwellings on sites under 1 hectare) can use the simplified Small Sites Metric, which eliminates the need for expensive multi-season full ecological baseline surveys.
All habitat creation must be maintained and monitored for at least 30 years, secured by Section 106 agreements, with regular ecological monitoring reports submitted to the council.
You cannot simply buy credits. Councils will reject applications that fail to prioritize on-site avoidance and enhancement before seeking private off-site habitat banks.
Frequently Asked Questions: Biodiversity Net Gain (BNG)
Statutory advice on 10% planning uplifts, Small Sites Metric rules, and credit pricing.
Under Schedule 7A of the Town and Country Planning Act 1990 (inserted by the Environment Act 2021), all major developments from February 2024 and small sites from April 2024 must achieve a minimum 10% net gain in biodiversity value compared to the pre-development baseline. The gain must be calculated using the statutory Defra Statutory Biodiversity Metric (or Small Sites Metric) and secured for at least 30 years via Section 106 legal agreements or conservation covenants.
Statutory Diligence Guides & Legal FAQs
Official regulatory answers referencing Acts of Parliament, RICS guidance, and statutory planning orders.
How Do You Calculate Statutory Biodiversity Net Gain (BNG) in the UK?
Biodiversity Net Gain (BNG) is calculated using the statutory Defra metric formula: Biodiversity Units = Baseline Habitat Area (hectares) × Habitat Distinctiveness (1 to 8) × Habitat Condition (1 to 3) × Strategic Significance (1.0 to 1.15). To secure planning permission under Schedule 7A of the Town and Country Planning Act 1990, developers must demonstrate that post-intervention units (on-site retained and enhanced habitats plus off-site units) equal at least 110% of the pre-development baseline score across each of the three mandatory unit types: area habitats, hedgerows, and watercourses.
What Are the Statutory Rules for Biodiversity Net Gain (BNG) in 2026?
In 2026, statutory Biodiversity Net Gain is mandatory for all major developments (since February 2024), small residential sites (since April 2024), and Nationally Significant Infrastructure Projects (NSIPs, mandated in 2026). Key statutory requirements include: (1) A legally binding minimum 10.0% net gain over pre-development baseline, (2) Submitting an approved Biodiversity Gain Plan before commencement of works, (3) Securing habitat enhancements for a minimum 30-year maintenance period via Section 106 agreements or Conservation Covenants, and (4) Registering off-site gains on Natural England's National Biodiversity Gain Site Register.
How Much Can Landowners Earn from Selling BNG Units in the UK?
Landowners establishing registered habitat banks can earn between £20,000 and £45,000 per biodiversity unit sold to developers. Marginal agricultural land typically generates 2 to 4 biodiversity units per hectare through wildflower meadow creation or woodland planting. A 20-hectare habitat bank yielding 60 net units can generate gross sales revenues of £1,200,000 to £2,100,000. After deducting 30-year habitat maintenance costs, monitoring fees, and legal covenant charges (£8,000–£15,000 per ha), landowners achieve net returns far exceeding traditional agricultural crop yields.
How Much Does 1 BNG Unit Cost? (Private Market vs Statutory Credits)
On the UK private market, 1 Biodiversity Net Gain (BNG) unit typically costs between £20,000 and £35,000 for standard grassland and scrub habitats, rising to £40,000–£55,000 for high-distinctiveness woodland or wetland habitats. In contrast, Government Statutory Biodiversity Credits sold directly by Natural England are intentionally priced punitively to protect the private market: statutory credits cost £42,000 (+VAT) for Tier A1, £48,000 for Tier A2, and up to £650,000 for scarce habitats. Furthermore, developers must purchase 2 statutory credits to satisfy every 1-unit deficit, making private off-site units at least 60% cheaper.
Biodiversity Net Gain Calculator Gov UK: Statutory Defra Metric Tool
The official Gov.uk statutory tool is the 'Statutory Biodiversity Metric'—a macro-enabled Microsoft Excel spreadsheet published by Natural England and Defra. It requires qualified ecologists to input Phase 1 or UKHab survey codes, parcel areas in hectares, strategic significance factors, and target condition assessments. While the official 25MB spreadsheet is mandatory for formal planning submissions, our fast web-based BNG calculator provides developers, architects, and landowners with instant feasibility modeling before hiring expensive ecology consultancies.
BNG Small Sites Metric (SSM): Rules & Calculator for Small Developments
The Small Sites Metric (SSM) is a simplified statutory calculation tool created by Natural England for minor developments. In residential schemes, it applies to developments between 1 and 9 dwellings on sites under 0.5 hectares (or under 0.2 hectares if dwelling numbers are unspecified). For non-residential schemes, it applies where floorspace is under 1,000 square metres or site area is under 1 hectare. Unlike the main metric, the SSM does not require a certified CIEEM ecologist to complete condition sheets if the site contains only low or medium distinctiveness common habitats.
Free Biodiversity Net Gain Calculator Online UK: 10% BNG Estimator
Our free online Biodiversity Net Gain Calculator allows property developers, architects, planning consultants, and self-builders to model statutory 10% BNG requirements in seconds. Input your development site area, select your existing baseline habitat types (arable, grassland, scrub, hardstanding), configure proposed on-site green infrastructure (gardens, bioswales, green roofs), and calculate your exact net gain or shortfall percentage. If a deficit occurs, the calculator automatically estimates required off-site units and statutory credit costs.
How to Buy Off-Site BNG Units and Statutory Credits in the UK
To buy off-site BNG units in England: (1) Confirm your exact unit deficit using the Statutory Biodiversity Metric, (2) Search Natural England's Biodiversity Gain Site Register or private environmental brokers to find an accredited habitat bank within your local planning authority or National Character Area, (3) Enter into a formal BNG Unit Purchase Agreement with the landowner/broker (£20,000–£40,000 per unit), (4) Obtain a formal Certificate of Unit Allocation referencing the registered gain site ID, and (5) Submit the certificate and Biodiversity Gain Plan to your council. Only if no local private units exist can you apply to Natural England to buy statutory credits.