Use this Biodiversity Net Gain checker to understand whether BNG may apply to a development in England before submitting a planning application. It reviews planning route, timing, site size, habitat impact, possible exemptions, Small Sites Metric suitability and likely next steps.
BNG rules are changing during 2026. This checker includes current GOV.UK guidance and announced DEFRA updates, but it should not replace ecological advice, the statutory metric or your local planning authority’s requirements.
Biodiversity Net Gain can affect the layout, cost, timing and planning strategy of a development. This checker is designed to help you spot whether BNG is likely to be relevant before you spend money on surveys, drawings or a planning application.
It does not calculate official biodiversity units. Instead, it gives a cautious screening result and explains what evidence or professional input may be needed next.
Answer the questions below. The result updates automatically and can also be refreshed using the button at the bottom.
The checker uses a cautious readiness score. Exemptions are treated carefully because habitat type, red line boundary and local validation evidence can change the result.
| Score | Result | Likely documentation | What it usually means |
|---|---|---|---|
| 0–2 | Low BNG risk / possible exemption | Exemption statement, red line plan, photos | The proposal may be exempt or low impact, but evidence may still be needed. |
| 3–5 | Evidence needed | Habitat evidence, measurements, red line plan | Do not rely on an exemption without clearer habitat evidence. |
| 6–9 | BNG likely applies | Small Sites Metric or ecological input | BNG is likely to form part of the planning route unless a clear exemption applies. |
| 10+ | High BNG planning risk | Ecologist, metric, habitat strategy, Biodiversity Gain Plan | The project may need stronger ecological input and a more developed BNG strategy. |
BNG is only one part of early-stage development feasibility. These related tools can help you test site yield, planning risk, GDV and wider viability.
Browse the full land development hub for housing yield, GDV, planning risk and feasibility calculators.
Estimate possible housing numbers from land size, density and site constraints.
Check common planning risk factors before spending heavily on a scheme.
Test development costs, GDV and margin assumptions before moving forward.
Calculate dwellings per hectare and test broad housing density assumptions.
Explore whether a plot or site may support subdivision and future development.
Plain-English answers to common questions about Biodiversity Net Gain, exemptions, small sites and ecology input.
No. This is an early screening checker. It does not calculate official biodiversity units and does not replace the statutory biodiversity metric, ecological advice or local planning authority requirements.
Householder applications are generally treated as exempt from mandatory BNG, but other ecology, tree, protected species or local validation requirements may still apply.
The de minimis exemption is for very small habitat impacts where no priority habitat is affected and the impact is below the relevant onsite habitat and linear habitat thresholds. Evidence may still be needed to support the exemption.
There is a current self-build/custom-build exemption where strict conditions are met, but government has announced that this exemption is expected to change during 2026. Always check the latest position before relying on it.
The Small Sites Metric is a simplified version of the statutory biodiversity metric for certain small developments. It may be suitable for some smaller schemes, but the site, habitat type and local planning authority requirements still matter.
Not every small site will need an ecologist, but ecological advice becomes more important where habitat types are uncertain, or where trees, hedgerows, ponds, ditches, watercourses, woodland, scrub or possible priority habitat may be affected.
If BNG applies and onsite delivery is not realistic, the scheme may need off-site biodiversity units or statutory biodiversity credits. Statutory credits are intended as a last resort and can become a material development cost.
This checker is designed to help you ask better questions before planning. If the result shows evidence needed, BNG likely applies or high BNG planning risk, consider checking the latest GOV.UK guidance, speaking to your local planning authority or getting ecological advice before submitting.
