It can apply to new development of 100 m² or more and to new dwellings of any size, but only where an operative charging schedule applies and after the relevant exemptions and deductions are considered. [1]
Start with the site and the development
The first question is not simply how large the extension will be. Identify the charging authority, the permission being implemented and whether the project creates a new dwelling. A small new house is not automatically outside CIL because its floor area is below 100 m². By contrast, an extension below that threshold which does not form part of development creating a dwelling normally benefits from the minor-development exemption. [2]
Permitted development is not a general escape from CIL. The system includes a notice for chargeable development granted by general consent, including permitted-development rights. Check the CIL position even when a full planning application is unnecessary. [3]
How the amount is worked out
A charging schedule identifies the rates for different locations and development types. The calculation uses gross internal area, with eligible existing floorspace taken into account and the applicable indexation applied. This is not necessarily the same area shown as saleable accommodation in an estate agent's particulars. [4][2]
For a budget estimate, ask for the proposed and existing floor areas to be shown separately, with the qualifying deductions explained. Then identify the actual rate, its date and any exemption being claimed. Do not combine an old unindexed rate with an unexplained net floor-area figure.
In London, the borough's CIL and the Mayor's CIL can both apply. Richmond's published guidance, for example, identifies its own charging schedule separately from Mayoral CIL. A calculation which includes only one may therefore miss part of the liability. [5]
Exempt does not always mean no paperwork
Reliefs exist for qualifying self-build homes, residential extensions and annexes, among other categories. For those household exemptions, applying and receiving confirmation before starting work is crucial. Saying on a planning application that the building is “self-build” does not replace the exemption procedure. [1]
Form 1 provides additional information so the authority can assess liability. It is not itself an exemption approval. Use the separate claim form where required, retain the written decision and establish whether a commencement notice is needed. [6][7]
A useful project file distinguishes the authority's liability calculation, any exemption decision, and the payment instructions. A low or zero estimate in an early cost plan should not substitute for those documents.
Epping Forest is different
On 2 October 2026, Epping Forest's website is consulting on an updated draft CIL charging schedule, with consultation running from 1 to 30 October 2026. The draft is not an operative tariff. Its proposed rates should not be presented as charges already payable on a district project. The council explains that CIL, if introduced, would operate alongside appropriate Section 106 obligations. [8]
Allow for later changes
CIL rates are indexed annually. Re-check the relevant annual rate summary for a later permission, rather than assuming a current example applies indefinitely. Epping Forest's proposed introduction also needs a further check once its consultation and subsequent formal stages have progressed. [2][8]