Calculating your CIL liability from the charging schedule

Your Community Infrastructure Levy charge is the chargeable floorspace multiplied by the rate in the council's charging schedule, indexed, less any floorspace you are entitled to deduct. Each of those three elements is a separate argument, and the deduction for existing floorspace is where most self-builders either save a great deal of money or lose it. The charge is calculated by the council, but it will calculate from the figures you supply, so a measurement error in your favour or against you tends to survive unchallenged.

Work the number out yourself before you submit. A charge that arrives as a surprise on a liability notice is a charge you have already lost the argument about.

Finding the charging schedule and the rate for your use

Not every authority charges the levy. Where one does, it adopts a charging schedule setting rates in pounds per square metre, and those rates vary by use and often by geographical zone within the district.

Find the current adopted schedule on the council's planning policy pages, along with any zone map. Read both together, because a residential rate can differ substantially between two sites a mile apart. Note the date of adoption, since the indexation calculation starts from it.

Residential is usually the highest rate. Retail, offices, industrial and community uses are often charged at nil or at a much lower figure, which matters when you are converting between them. Where your development includes more than one use, each is charged at its own rate on its own floorspace.

Measuring gross internal area correctly

The levy is charged on gross internal area, which is a different measurement from the gross external floorspace used to calculate the planning application fee. Getting the two confused is a common and expensive slip.

Gross internal area is measured to the internal face of the external walls, across every storey, including circulation, plant rooms, integral garages, and usable roof space with adequate headroom. It excludes open balconies and open external areas.

Two habits protect you. Have the area scheduled by whoever prepared the drawings, room by room and floor by floor, rather than taking a single figure from a design and access statement. And keep the schedule, because if the council's figure differs from yours, the schedule is your evidence.

Where your scheme has mezzanines, basements or a converted loft, measure them explicitly and state whether you have included them. Silence on a basement invites the council to assume its own figure.

Deducting existing floorspace and the in use test

This is the provision that decides whether a conversion or replacement dwelling pays anything at all. You can deduct the gross internal area of existing buildings that are to be demolished or retained and reused, but only where the building satisfies the in use test.

The test, in substance, is that the building must have been in lawful use for a continuous period of at least six months within a defined period ending on the day planning permission first permits the chargeable development. The building also has to be a relevant building, meaning it contains a part that has been in lawful use.

Three points decide most cases:

1. Lawful use means use in accordance with planning control, so a building used without the necessary permission does not qualify.
2. Continuous means continuous, and a barn that has stood empty for years will fail however substantial it is.
3. Evidence is on you. Utility bills, council tax or business rates records, tenancy agreements, photographs with dates and statements from occupiers all help. Assemble them before you apply.

A barn conversion where the building has stood disused is the classic case where the deduction fails and the charge lands in full. If your scheme depends on the deduction, establish the evidence position before you commit to the purchase price.

How indexation is applied

Rates in the charging schedule are stated at the date of adoption and are then indexed. The regulations set out the formula, which uses a published index of build costs, and the calculation applies the index figure for the year in which planning permission was granted against the figure for the year the schedule took effect.

Two practical consequences. The rate you pay is higher than the rate printed in the schedule, sometimes considerably so on an older schedule. And the relevant year is the year permission was granted, so a permission granted in December and one granted the following January can be indexed differently.

Councils publish the indexed rates they are currently applying. Ask for them rather than calculating the index yourself, then check the arithmetic.

The liability notice and checking it

Once permission is granted the council issues a liability notice setting out the chargeable amount. Read it against your own calculation line by line.

Check the floorspace figure, the rate applied and its zone, the index figure and year, and the deduction for existing floorspace. Check that the use has been correctly classified, particularly on a mixed use scheme. And check the assumed commencement position, since the notice interacts with the liability notices, commencement notices and surcharge regime that follows it.

If you disagree, raise it immediately and in writing. There are formal review and appeal routes with short deadlines, and an informal conversation that drifts past those deadlines leaves you with the council's figure.

Instalment policies and exemptions

Where the authority has adopted an instalment policy, the charge is payable in tranches tied to periods after commencement. Where it has not, the full amount falls due shortly after commencement, which for a self-builder is the worst possible moment in the cash flow.

Check the instalment policy before you plan the funding, and check whether it is lost if you fail to submit a commencement notice. In several authorities it is.

Self-build exemption removes the charge entirely for a dwelling you build and occupy as your main residence, and there are separate exemptions for residential extensions and annexes. All of them have to be claimed and granted before you start work, and the self-build exemption requires supporting evidence after completion as well. Missing the commencement notice can cause an exemption already granted to be withdrawn.

Challenging a calculation

Four routes exist, and they have different grounds and different deadlines.

Ask the council to review the chargeable amount, which is the first step and the one with the tightest time limit. Appeal to the appointed body on the chargeable amount if the review does not resolve it. Appeal separately against the imposition of a surcharge, or against a determination that development has begun. And, where the dispute is about whether the levy applies at all rather than about the arithmetic, take planning advice, because that is a different question.

Do not simply pay under protest and hope to argue later. The routes are time-limited, and the practical answer is to calculate the charge before you submit the application, so the liability notice confirms a figure you already expected. Where you are budgeting the whole application rather than just the levy, PlanScope pricing sets out what the supporting documents cost, and the full report index shows which ones a constrained site is likely to need.

This is general guidance, not legal advice. Check the position with your local planning 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.