How a CIL charge is calculated on a new dwelling

A Community Infrastructure Levy calculation is arithmetic, not judgement. The charging authority takes the rate from its adopted charging schedule, applies it to the chargeable floor area, deducts any qualifying existing floorspace, and adjusts the result using an index published annually. Get any one of those four inputs wrong and the demand notice is wrong, which happens often enough that checking the calculation is worth an hour of anyone's time.

The formula sits in the Community Infrastructure Levy Regulations 2010. What it charges is new floorspace, measured as gross internal area, in the area covered by a charging schedule.

What the levy charges and what it does not

The levy applies to development that creates new build floorspace, and typically to the creation of a new dwelling regardless of size. Not every authority charges it: an authority must have adopted a charging schedule after examination, and some have not.

Rates are set per square metre and vary by use and by geography within the authority's area. A residential rate in a high value zone can be several times the rate in a low value zone of the same district, which is why the zone your site falls in matters as much as the rate itself.

Some development is outside the charge entirely, including buildings into which people do not normally go, and development where the chargeable area after deductions is less than 100 m² unless it creates a dwelling. That last qualification catches small new houses: a 70 m² new dwelling is chargeable even though 70 m² of extension would not be.

Measuring the chargeable area

The measurement is gross internal area, which is larger than the floor area most people quote from an estate agent's particulars.

Gross internal area includes internal walls and partitions, stairwells and lift shafts measured at each floor level, plant rooms, integral garages, and internal circulation. It is measured to the internal face of the external wall.

Two practical points. Mezzanines and loft areas with permanent access and adequate headroom generally count, so a room in the roof adds chargeable area. And integral garages count while detached garages may be treated differently, which makes the difference between an attached and a detached garage a real financial decision on a self-build plot.

Measure from the approved drawings and set the calculation out floor by floor. Where you disagree with the authority's figure, a floor by floor schedule is what resolves it.

One more measurement trap. Covered areas that are open on one or more sides, such as a car port or a recessed entrance, are treated differently from enclosed space, and the treatment can turn on how the drawings show the enclosure. If the design is close to a threshold, ask the authority how it intends to measure before the drawings are finalised rather than arguing about it after the liability notice arrives.

The deduction for existing floorspace

This is where most of the money is, and where most errors occur.

Floorspace in an existing building on the site can be deducted, but only where the building has been in lawful use for a continuous period of at least six months within the three years ending on the day planning permission first permits the chargeable development. The building must also be a building into which people normally go.

Three consequences follow.

A house that has been empty for years before redevelopment may not qualify, and the deduction can be lost entirely. Evidence of occupation matters: council tax records, utility bills, tenancy agreements and electoral roll entries.

Demolishing before the permission is granted does not remove the deduction if the building was there and in lawful use at the relevant date, but it makes the evidence harder to produce. Measure and photograph the existing building before it comes down.

And a building without planning permission for its current use is not in lawful use, so an unauthorised conversion cannot be deducted. Where a building has become immune from enforcement, a lawful development certificate is the way to establish the position, and the wider cost of putting unauthorised work right is covered in the cost of an unauthorised development put right.

Applying the rate and the index

Once the net chargeable area is settled, the rate from the charging schedule is applied, and the result is adjusted by an index.

The indexation mechanism uses a published construction cost index, comparing the index figure for the year the permission was granted with the figure for the year the charging schedule took effect. Where a charging schedule was adopted years ago, indexation can add a substantial amount to the headline rate.

Because the index is published annually and the rates are set locally, never quote a levy figure from another site or another year. Take the rate from the authority's current published charging schedule and the index figures the authority itself uses.

Note that a section 73 permission is a new permission for levy purposes, with the amount recalculated and credit given for the sum payable under the original. On a scheme with rising indexation, that recalculation can increase the liability even where the floorspace is unchanged.

Liability notices, commencement notices and demand notices

The sequence is procedural and unforgiving.

1. The authority issues a liability notice after planning permission is granted, setting out the chargeable amount and the payment arrangements.
2. Someone assumes liability, in writing, on the prescribed form. If nobody does, liability falls on the landowner and the payment options narrow.
3. Any relief or exemption is claimed and granted before development starts.
4. A commencement notice is submitted before development begins, stating the intended commencement date.
5. The authority issues a demand notice after commencement, and payment follows on the stated schedule or the authority's instalment policy.

Miss step four and the consequences are immediate: instalment rights can be lost, surcharges apply, and any exemption claimed can be withdrawn. Self-builders lose exemptions this way every year, having done everything else correctly.

Commencement has a wide meaning here. A material operation such as digging a foundation trench, laying a road or demolishing part of a building can start the clock, and site clearance sometimes counts. Assume the trigger is earlier than you think, and serve the notice before the contractor mobilises rather than on the day work starts.

Checking a calculation you disagree with

Start with the arithmetic and the inputs, in this order: the rate and zone, the gross internal area measurement, the existing floorspace deduction, and the index figures.

Where the figure is still wrong, the Regulations provide a review and appeal route. The first step is a request to the charging authority to review the chargeable amount, made within a short period of the liability notice. If the review does not resolve it, an appeal on the chargeable amount is determined by a valuation officer at the Valuation Office Agency.

Other appeal routes exist for apportionment of liability, for surcharges and for the determination of a deemed commencement date, each with its own short deadline.

The deadlines are the point. Levy appeal periods are measured in days from the relevant notice, and they are not extended for good reasons. Diarise the date the liability notice arrives.

Budget the levy alongside the application fee and the evidence base rather than treating it as a late surprise, and compare it against the cost of the documents themselves. The supporting reports a scheme needs and PlanScope pricing are separate lines from the levy, and on a single plot the levy is usually the largest of the three.

This is general guidance, not legal advice. Levy rates, indexation and procedural deadlines change, so check the current charging schedule with your charging authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.