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Biodiversity net gain calculator

Habitat units for baseline and post-development on Defra’s biodiversity metrics, with the working shown for every parcel. Area habitats module.

First — which metric applies?

Defra publishes two. This decides between them.

Baseline — habitat on site now

Post-development — habitat created or enhanced

What this covers, and what it doesn’t

  • Area habitats only. Hedgerows and watercourses are separate modules with their own tables. Their units are not interchangeable with area units — Defra reports all three separately and the 10% test applies to each, so a scheme can pass on area and still fail on hedgerows.
  • Both of Defra’s current metrics. The Statutory Biodiversity Metric v1.0.4 for the general case, and the Small Sites Metric v1.2.3 where a scheme qualifies. The numbering misleads — 1.0.4 is newer than the superseded Metric 4.0, and the Small Sites Metric is a separate tool rather than a version of either. Screening above decides, and anything unresolved sends you to the statutory metric, which is always acceptable.
  • Irreplaceable habitat produces no units. Ancient woodland and the rest cannot be traded off; they need bespoke compensation agreed with the planning authority. The calculator says so rather than returning a number.
  • Creation and enhancement are different jobs. Many habitats score them at different technical difficulty, and the waits differ — so the type is asked for rather than assumed.
  • This is not a Biodiversity Gain Plan. It is the arithmetic. A plan needs the site details, the irreplaceable-habitat position and the significance justification alongside it.

Runs entirely in your browser. Nothing you type is sent anywhere or stored. Figures follow Defra’s published tables; check anything you rely on against the statutory tool before submitting it.