CIL Calculation: How the Charge Is Worked Out

 

A CIL calculation is not simply the local rate multiplied by the extra floorspace. In England the collecting authority must calculate the charge under Schedule 1 to the Community Infrastructure Levy Regulations 2010. That means the result can depend on the applicable rate, gross internal area, existing buildings, demolition, different uses, indexation and any relief or exemption.

That is why two developments with the same amount of new floorspace can produce very different CIL bills.

 

How a CIL calculation works

 

For development in England, regulation 40 now sends the collecting authority to Schedule 1 of the CIL Regulations. Older guides which reproduce the former regulation 40 floorspace formula can therefore be misleading.

In a standard case, the authority identifies every relevant CIL rate which applies to the development and calculates the amount at each rate. Those amounts are then added together. If the final chargeable amount is less than £50, Schedule 1 treats it as zero.

The headline formula for each relevant rate is:

R × A × I_P / I_C

In plain English, that takes the applicable CIL rate, applies it to the deemed net area chargeable at that rate, and then adjusts the result for indexation.

 

Start with the correct CIL rate

 

The rate comes from the charging schedule which applies to the development. A charging schedule can set different rates for different uses, different parts of the charging area, or other categories permitted by the Regulations. Some development may be charged at a nil rate.

Where more than one rate applies within the same development, Schedule 1 requires a separate calculation for each rate. The authority then aggregates the results.

Do not rely only on the original charging schedule figure. Regulation 121C requires charging authorities to publish an annual CIL rate summary showing the indexed rates which apply for the next calendar year. Our Who charges CIL? guide helps identify charging areas, but the authority’s current charging schedule and annual rate summary should always be checked for the site itself.

 

Gross internal area is the starting floorspace

 

Schedule 1 uses gross internal area, usually shortened to GIA. This is not the same as adding together the usable floor areas of individual rooms, and it is not safe to assume that every space inside the external walls necessarily produces the same CIL result.

Lofts are a good example. A 2026 VOA appeal accepted one loft area shown with permanent stair access but rejected other roof spaces reached through loft hatches on the evidence before it. That did not create a rule that every loft without a staircase is excluded, but it shows why the measured floor level, access, plans and evidence matter. See our CIL loft floorspace appeal analysis.

For a development with several uses or rate zones, Schedule 1 also distinguishes the total GIA of the chargeable development from the GIA chargeable at each particular rate.

 

The deemed net area is not just new floorspace minus old floorspace

 

For a standard case Schedule 1 calculates the deemed net area, A, using:

A = G_R − K_R − (G_R × E / G)

The letters have specific jobs:

• G is the total gross internal area of the chargeable development
• G_R is the gross internal area of the part chargeable at the particular rate being calculated
• K_R covers qualifying retained existing floorspace chargeable at that rate
• E includes qualifying floorspace in in-use buildings which is to be demolished before the development is completed, with additional rules for later phases

The formula matters where several CIL rates apply because demolished floorspace is apportioned through the formula rather than simply being deducted from whichever part of the scheme produces the largest bill.

 

Existing buildings do not automatically reduce CIL

 

A building standing on the site is not automatically a credit against the CIL calculation. Schedule 1 has separate tests for retained floorspace and demolition floorspace.

An in-use building must be a relevant building and contain a part which was in actual lawful use for one continuous period of at least six months during the three years ending on the day planning permission first permits the chargeable development. The High Court in R (Hourhope Ltd) v Shropshire Council [2015] EWHC 518 (Admin) confirmed that having a lawful use on paper is not enough. The use must actually have been carried on.

There is also a separate retained-building route within K_R for some parts of other relevant buildings where the intended use after completion could have been carried on lawfully and permanently in that part without further planning permission on the day before the first-permits date.

Evidence is critical. Schedule 1 expressly allows the authority to treat a relevant building as not in use, or the relevant area as zero, if it does not have sufficient information of sufficient quality. The recent High Court decisions in Herod and Segrue make the practical risk of weak evidence and missed challenge deadlines particularly clear.

 

CIL indexation can materially change the figure

 

The rate in a charging schedule is indexed. For 2020 onwards Schedule 1 uses the RICS CIL Index published in November of the preceding year. The formula compares the index for the year in which planning permission was granted, I_P, with the index for the year in which the charging schedule containing the rate took effect, I_C.

For an outline permission there are special rules. Where a later charging schedule comes into force before the outline permission first permits development, Schedule 1 can preserve the charging schedule which was in force when the outline permission itself was granted.

This is one reason a simple online multiplication using the historic schedule rate can give the wrong answer.

 

A simple worked CIL calculation

 

Take a deliberately simple example with one rate, no existing-building deduction, no demolition and no relief. Assume the development has 100 m² of deemed net chargeable area, the applicable schedule rate is £100 per m² and the index ratio I_P / I_C is 1.20.

The calculation is:

£100 × 100 × 1.20 = £12,000

That example is only to show how the standard formula operates. A real development may involve several rates, existing floorspace, demolition, phases, relief, a section 73 permission or a pre-CIL permission, all of which can change the calculation.

 

Section 73 permissions use special calculation rules

 

A later permission under section 73 is not simply recalculated from scratch using today’s rate. Part 2 of Schedule 1 compares the notional amount under the new permission with the notional amount under the earlier permission. Separate rules apply where the new amount is the same, higher or lower.

There are further provisions for relief carried over to a section 73 permission and for CIL already paid. This is one of the areas where the calculation becomes technical very quickly. Our CIL section 73 guide explains the levy calculation, while our general section 73 planning guide explains the planning route itself.

 

What if the CIL calculation looks wrong?

 

Do not wait until the development starts. If you disagree with the chargeable amount in a Liability Notice, the normal route is to ask the collecting authority for a regulation 113 review within 28 days of the Liability Notice. If the dispute remains, a regulation 114 appeal to the Valuation Office Agency normally has to be made within 60 days of the original Liability Notice.

Commencement is crucial. Starting the chargeable development can prevent a review or appeal being made, or cause an existing challenge to lapse, subject to the limited retrospective-permission exception. Our CIL appeals guide explains the available routes and deadlines.

If the underlying planning application itself is refused, that is a different issue and the ordinary planning appeal route may be available.

 

Planning application costs are separate from CIL

 

CIL is a development levy, not the fee for making the planning application. The application fee depends on the planning route and development proposed. See our planning application fees guide.

 

Relevant CIL calculation rules

 

• Regulation 40: calculation of chargeable amount in England
• Schedule 1: calculation of chargeable amount
• Government Community Infrastructure Levy guidance
• VOA CIL appeal decisions

Community Infrastructure Levy (CIL)

 

CIL Calculation Page Updated: 30th August 2026