CIL Calculator

The Community Infrastructure Levy (CIL) Calculator is essential for UK property developers planning new developments. CIL is a planning charge that funds local infrastructure—schools, roads, parks, and community facilities. Understanding your CIL liability is critical for accurate development appraisals.

What is CIL?

CIL was introduced under the Planning Act 2008 to provide local authorities with a more predictable funding stream for infrastructure than the previous system of negotiated S106 agreements. Unlike S106, CIL is a fixed charge per square metre based on:

- Local authority charging rates - Development type and location - Net additional floor area - Available reliefs and exemptions

How CIL is Calculated

The basic CIL formula is:

CIL = Chargeable Area (sqm) × Indexed CIL Rate (£/sqm)

But the calculation involves several adjustments:

1. Net Additional Floor Area: Start with your proposed gross internal area (GIA). If demolishing existing buildings that have been in lawful use for 6+ months in the last 3 years, you can deduct that floor area.

2. Apply Reliefs: Reduce the chargeable area for: - Social housing relief (100% for qualifying affordable housing) - Self-build exemption (100% if building your own home) - Charitable relief (for charitable purposes)

3. Index the Rate: CIL rates are indexed annually using the BCIS All-in Tender Price Index. A rate adopted at £100/sqm in 2020 might be £123/sqm in 2024 after indexation.

4. Calculate Liability: Multiply chargeable area by indexed rate.

CIL Rates by Local Authority

CIL rates vary dramatically:

- Westminster Prime: £550/sqm for residential - Tower Hamlets Zone 1: £200/sqm - London Mayoral CIL: £25-80/sqm (on top of borough CIL) - Manchester City Centre: £50/sqm - Many provincial areas: £0 (CIL not adopted)

Check your local authority's Charging Schedule—they're publicly available online.

Available Reliefs

Social Housing Relief: Affordable housing provided by registered providers qualifies for 100% relief. The housing must meet the definition in CIL Regulations and remain affordable in perpetuity. Apply before commencement.

Self-Build Exemption: Building your own home? Full exemption available if you: - Apply before commencement - Occupy as your main residence - Live there for minimum 3 years - Weren't a professional developer

Charitable Relief: Development by charities for charitable purposes may qualify.

Exceptional Circumstances Relief: Discretionary—rarely granted. Must prove the development would be unviable with CIL.

Payment Schedule

CIL payment timing depends on total liability:

- Under £50,000: 100% due on commencement - £50,000-£500,000: 50% on commencement, 50% at 60 days - Over £500,000: 25% instalments at 0, 60, 120, and 180 days

Failure to pay triggers surcharges (20% after 30 days, 40% thereafter) plus 8% interest. The council can issue stop notices halting construction.

CIL vs S106

CIL and S106 serve different purposes:

- CIL: Fixed charge funding general infrastructure - S106: Negotiated contributions for site-specific mitigation

CIL cannot fund the same infrastructure as S106. Most schemes pay both. Some authorities have low CIL but high S106; others have high CIL and minimal S106.

Impact on Development Appraisals

CIL directly affects viability:

- Reduces profit on cost - Increases total development cost - May affect maximum land bid - Front-loads cash requirements

Always include CIL in your appraisal from feasibility stage. Factor in indexation if commencement is 1-2 years away.