BNG Calculatorv4.0 / JP039
Statutory Biodiversity Metric v4.0 (JP039)· Defra GOV.UK guidance, last updated 2 June 2026· NSIP extension live 2 November 2026· Reviewed 21 June 2026

BNG temporal risk multiplier: years-to-target discount table

Temporal risk discounts post-development units by the Defra 3.5% rate compounded over years-to-target-condition; long-target habitats like woodland and fen lose 30% to 60% of their nominal score.

Awaiting MCIEEM peer review · CIEEM (Chartered Institute of Ecology and Environmental Management)

The discount formula

Multiplier = 1 / (1 + 0.035)^years; the Defra discount rate is 3.5%. Five-year target condition: 0.842; ten-year: 0.709; twenty-year: 0.503; thirty-year: 0.355.[S1]

Why woodland is punished heavily

Lowland mixed deciduous woodland creation has a 30-year target condition under JP039 condition cards; the temporal multiplier discounts the unit yield to 0.355 of the headline score. Combined with the difficulty multiplier (high difficulty = 0.333), a woodland creation can deliver under 12% of its raw distinctiveness-times-condition score in the metric.

How habitat banks beat the multiplier

Habitat banks that have already established the habitat by the time the unit is sold do not carry the temporal discount; the buyer pays for delivered units, not promised future condition. This is the structural reason habitat bank prices clear above on-site delivery cost for the same habitat type.

Discount table (selected years)