Non-statutory estimator · v1.0 · 17 September 2026
Biodiversity net gain calculator
This biodiversity net gain calculator from Biodiversity Net Gain Hub is a non-statutory estimator for England. It applies the statutory biodiversity metric's area-habitat logic (area × distinctiveness × condition × strategic significance, with difficulty and temporal discounts for created habitat) to show an indicative baseline, the 10% target and any shortfall. It is educational only: planning applications need the statutory biodiversity metric tool completed by a competent ecologist.
Inputs
Describe every parcel of habitat inside your red line boundary as it is today (baseline), then describe the site as it will be when the development is complete (post-development). Areas are in hectares (1 ha = 10,000 m²). The tool starts with the worked example shown further down so you can see how the arithmetic behaves.
Baseline (pre-development) parcels
| Habitat type | Area (ha) | Condition | Strategic significance | Actions |
|---|
Post-development parcels
| Habitat type | Area (ha) | Intervention | Target condition | Strategic significance | Difficulty | Years to target | Actions |
|---|
Results
Results appear here once JavaScript has loaded.
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The summary below is plain text and includes the version, date and the educational-only statement, so it cannot be mistaken for a statutory calculation.
Assumptions (versioned, visible without JavaScript)
Version 1.0, 17 September 2026. Every figure used by the estimator is listed here. They reflect the structure of Defra's statutory biodiversity metric as described on GOV.UK, simplified for education. The statutory tool contains many more habitat types, condition criteria, trading rules and linear-habitat modules that this estimator does not attempt.
| Band | Score |
|---|---|
| Very low | 0 |
| Low | 2 |
| Medium | 4 |
| High | 6 |
| Very high | 8 |
| Condition | Score |
|---|---|
| Not assessed / n/a (very low distinctiveness) | 1 |
| Poor | 1 |
| Fairly poor | 1.5 |
| Moderate | 2 |
| Fairly good | 2.5 |
| Good | 3 |
| Level | Multiplier |
|---|---|
| Low — not in a local strategy | 1 |
| Medium — location ecologically desirable | 1.1 |
| High — identified in Local Nature Recovery Strategy | 1.15 |
| Difficulty | Multiplier |
|---|---|
| Low | 1 |
| Medium | 0.67 |
| High | 0.33 |
| Very high | 0.1 |
- Temporal multiplier: (1 − 0.035) raised to the number of years to target condition, i.e. a 3.5% discount per year. Five years ≈ 0.837; ten years ≈ 0.700; thirty years ≈ 0.344.
- Target: baseline units × 1.10 (the statutory minimum 10% gain). Some local plans seek more where justified.
- Very-low distinctiveness habitat (sealed surface, hardstanding) scores 0 units regardless of condition.
- Statutory credits (illustrative last resort): shortfall × 2 (spatial risk multiplier) × tier price. Tier prices used: A1 £42,000, A2 £48,000, A3 £66,000, A4 £125,000, A5 £650,000 per credit (GOV.UK, updated 2 June 2026). The estimator shows an A1–A4 range because the true tier depends on the habitat being compensated.
| Habitat | Broad type | Distinctiveness | Typical years to target | Creation difficulty | Credit tier |
|---|---|---|---|---|---|
| Developed land: sealed surface (buildings, tarmac) | Urban | Very low (0) | 0 | Low | A1 (£42,000) |
| Artificial unvegetated, unsealed surface (gravel, hardstanding) | Urban | Very low (0) | 0 | Low | A1 (£42,000) |
| Cereal crops / arable field | Cropland | Low (2) | 1 | Low | A1 (£42,000) |
| Modified grassland (amenity, improved pasture, lawn) | Grassland | Low (2) | 1 | Low | A1 (£42,000) |
| Vegetated garden | Urban | Low (2) | 1 | Low | A1 (£42,000) |
| Other neutral grassland (species-rich, non-priority) | Grassland | Medium (4) | 5 | Low | A1 (£42,000) |
| Mixed scrub | Heathland and shrub | Medium (4) | 5 | Low | A1 (£42,000) |
| Urban tree planting / street trees (area equivalent) | Individual trees | Medium (4) | 10 | Low | A1 (£42,000) |
| Other woodland, broadleaved (non-priority) | Woodland and forest | Medium (4) | 25 | Medium | A2 (£48,000) |
| Pond (non-priority) | Lakes | Medium (4) | 5 | Medium | A4 (£125,000) |
| Lowland meadows (priority habitat) | Grassland | High (6) | 15 | High | A1 (£42,000) |
| Lowland heathland (priority habitat) | Heathland and shrub | High (6) | 15 | High | A2 (£48,000) |
| Reedbeds (priority habitat) | Wetland | High (6) | 10 | Medium | A1 (£42,000) |
| Wet woodland (priority habitat) | Woodland and forest | High (6) | 30 | High | A3 (£66,000) |
| Lowland mixed deciduous woodland (priority habitat) | Woodland and forest | High (6) | 30 | High | A4 (£125,000) |
| Lowland fens (priority habitat) | Wetland | Very high (8) | 30 | Very high | A4 (£125,000) |
Worked example
A 1.0 hectare site in England: 0.6 ha of modified grassland in moderate condition and 0.4 ha of existing buildings and tarmac. The scheme builds on 0.65 ha, keeps 0.2 ha of the grassland and creates 0.15 ha of species-rich neutral grassland expected to reach moderate condition in five years. Strategic significance is low throughout.
| Stage | Parcel calculation |
|---|---|
| Baseline | 0.60 ha × D 2 × C 2 × SS 1 = 2.40 units |
| Baseline | 0.40 ha × D 0 × C 1 × SS 1 = 0.00 units |
| Post-development | 0.20 ha × D 2 × C 2 × SS 1 = 0.80 units (retained) |
| Post-development | 0.15 ha × D 4 × C 2 × SS 1 × difficulty 1 × temporal 0.837 (5 yrs) = 1.00 units (created) |
| Post-development | 0.65 ha × D 0 × C 1 × SS 1 × difficulty 1 × temporal 1.000 (0 yrs) = 0.00 units (created) |
| Baseline total | 2.40 units |
| Target (× 1.10) | 2.64 units |
| Post-development total | 1.80 units |
| Indicative shortfall | 0.84 units → ≈ 1.67 statutory credits → £70,208 to £208,951 illustrative (A1–A4) |
Reading it: the scheme loses about half its biodiversity value, so even with new habitat on site it falls roughly 0.8 units short of the 10% target. The developer's realistic routes are more on-site habitat (for example, retaining more grassland or planting trees), buying off-site units of a suitable grassland type from a registered gain site, or, only if neither is possible, statutory credits.
How to read the results
- Baseline units are what the site is worth today. The higher the baseline, the more you must deliver.
- Target units are baseline × 1.10. This is the number the approved biodiversity gain plan must reach.
- Post-development units count retained habitat at full value and created or enhanced habitat at a discounted value because it is uncertain and takes time.
- Shortfall is what must be met off-site or with statutory credits. Under the biodiversity gain hierarchy you must show you have tried on-site first (small developments may consider on-site and off-site together from 6 August 2026).
- Checks flag mismatched areas, the 0.2 ha exemption threshold and high-distinctiveness habitat that triggers trading rules.
Limitations
- Area habitats only. Hedgerows and watercourses have separate linear unit modules in the statutory metric that this estimator does not model.
- No trading rules. The statutory metric requires like-for-like or better compensation for medium and higher distinctiveness habitat, and treats irreplaceable habitat separately.
- Condition is self-declared here; in practice it follows published condition assessment criteria applied by a competent surveyor.
- Strategic significance depends on the Local Nature Recovery Strategy and local plan for your site.
- Off-site units also carry a spatial risk multiplier by distance from the development, which is not modelled.
- The habitat list is an illustrative subset. The statutory tool covers many more types with specific rules.
- Estimates are not a quotation, valuation or legal advice, and they are not a statutory metric output.
Next steps
Frequently asked questions
How do you calculate biodiversity net gain?
Biodiversity net gain is calculated with the statutory biodiversity metric. For each area habitat parcel, biodiversity units equal area in hectares multiplied by distinctiveness, condition and strategic significance scores. The baseline total is the pre-development value; the target is that total plus 10%. Post-development units for created or enhanced habitat are further multiplied by difficulty and temporal risk factors. If post-development units fall short, the difference is met with registered off-site units or, as a last resort, statutory credits.
Is this the official BNG calculator?
No. The official tool is Defra's statutory biodiversity metric calculation tool (and the small sites metric for eligible small developments), published on GOV.UK. The Biodiversity Net Gain Hub estimator is a simplified, non-statutory model for orientation; its outputs cannot be submitted with a planning application or biodiversity gain plan.
Do I need an ecologist to calculate BNG?
For most developments, yes. GOV.UK states that a developer or land manager should hire a competent person such as an ecologist to use the statutory metric tool, and a local planning authority may reject calculations it does not believe were completed by a competent person. The exception is a qualifying small development using the small sites metric, which a non-ecologist familiar with the site may complete.
How much does BNG cost?
Costs depend on how many biodiversity units are lost and how they are replaced. On-site design changes are usually cheapest. Off-site units are traded privately at market prices. Statutory credits, the last resort, are priced by Defra from £42,000 per credit (tier A1) to £650,000 (tier A5), with hedgerow credits at £44,000 and watercourse credits at £230,000 (prices page updated 2 June 2026), and a spatial risk multiplier means you buy 2 credits for every unit needed. Survey, metric and legal costs are additional.
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Sources
Official guidance this page relies on, with the "last updated" date shown on each source when this page was written. Always check the live GOV.UK page before acting.
- Calculate biodiversity value with the statutory biodiversity metric — GOV.UK (Defra) (updated 14 July 2026)
- Statutory biodiversity metric tools and guides — GOV.UK (updated 2 June 2026)
- Statutory biodiversity credit prices — GOV.UK (Defra) (updated 2 June 2026)
- Understanding biodiversity net gain — GOV.UK (Defra) (updated 14 July 2026)
- Biodiversity net gain: exempt developments — GOV.UK (Defra) (updated 6 August 2026)