BNG calculator: does biodiversity net gain apply to your site?

Answer a handful of questions for an instant verdict: exempt (and under which regulation), Small Sites Metric route, or full statutory metric - plus a rough worst-case cost of the units. Updated for the exemption changes in force 6 August 2026 (SI 2026/790). England only.

1The development

2The site

3Rough cost

4Results

Where is the site? This tool applies England's statutory BNG only. Wales, Scotland and Northern Ireland work differently - for Wales, the one quantified regime is nutrient neutrality: try our nutrient neutrality calculator.

What kind of development?

When is (or was) the application made? The exemption set changed on 6 August 2026. s73 applications follow the date of the original application or permission.

Red-line site area (hectares) 1 ha = 10,000 m2. The new 0.2 ha exemption turns on this number.

Number of dwellings

Not sure yet

Entirely self-build or custom-build? Exemption removed for applications from 6 August 2026.

Temporary permission only (up to 5 years)? Temporary development became exempt on 6 August 2026 (reg 7B).

How much habitat will the works affect? Under 25 m2 of habitat (or 5 m of hedgerow) with no priority habitat is exempt as de minimis.

Priority habitat on site? Voids the small-site exemptions and bars the Small Sites Metric. Check the Magic Map inventory.

Designated site or protected species? SSSI, SAC, SPA, Ramsar; bats, newts etc. Bars the Small Sites Metric.

Hedgerow, ditch or stream on site? Measured in their own metric modules - area gains cannot cover them.

Optional: if the dominant habitat on site is lost entirely, how many units would you owe, and what might they cost? Worst case - a real metric with retention usually comes out lower.

Dominant existing habitat

Condition

Habitat area lost (ha) Pre-filled with your red-line site area - the worst case is losing all of it.

The rules this tool applies (2026)

The 10% floor. Most planning permissions in England must deliver at least a 10% increase in biodiversity value, measured by the statutory biodiversity metric - and some local plans demand more (e.g. 20%), so check the LPA's adopted plan before assuming 10%.
Three separate modules. Area habitats, hedgerows and watercourses are measured and gained separately - you cannot offset a watercourse loss with grassland units.
Exempt at any date: householder applications; de minimis impacts (under 25 m2 of habitat or 5 m of hedgerow, no priority habitat); applications made before 12 February 2024.
New from 6 August 2026 (SI 2026/790): sites of 0.2 ha or less are exempt where no priority habitat is impacted (reg 7A); temporary permissions of up to 5 years are exempt (reg 7B); and the self/custom-build exemption is removed for new applications.
Small Sites Metric: a simplified route for 1-9 dwellings on up to 1 ha (or non-residential under 1,000 m2 / under 1 ha) - but never where priority habitats, protected sites or protected species are present.
If BNG applies: a Biodiversity Gain Plan must be approved before commencement, habitats must be managed for at least 30 years, and off-site units or statutory credits (the costly last resort - you buy two credits per unit of shortfall) are only for what cannot be delivered on site.

Rules as at 1 August 2026: statutory biodiversity metric (v1.0.4) + user guide; SI 2026/790 in force 6 August 2026; statutory credit prices as published November 2023. Sources: gov.uk BNG guidance and legislation.gov.uk (OGL).

Indicative only. This screener is not a substitute for the official statutory metric and Small Sites Metric tools, the gov.uk BNG guidance, or advice from a competent person (in practice, an ecologist for anything beyond the Small Sites Metric). Exemption verdicts depend on your answers being accurate - a "not sure" is treated cautiously, never as proof of the answer that suits you. The cost figures are worst-case indicators (total habitat loss, no retention, low strategic significance); a properly prepared metric with on-site retention will usually come out lower. The tool applies England's statutory BNG only. It does not bind the LPA or the Secretary of State.

No liability. This is general information, not planning, legal or ecological advice, and using it creates no professional relationship. GapSense accepts no liability for any loss arising from reliance on this tool - always verify the position with the local planning authority and a qualified professional before acting on an exemption verdict or a cost figure.