TRANSPARENCY
How we calculate your project estimates
We believe you deserve complete transparency about where our estimates come from and what they mean for your project. Here's exactly how we calculate costs, timelines, and regional adjustments – with honest guidance about their limitations.
Cost calculation methodology
Our estimates are built on real world project data, not theoretical calculations
Being genuinely independent means we can be completely honest about our methodology. We don't profit from which builder you choose or which professional you hire, our success depends solely on providing accurate, trustworthy guidance.
You need cost clarity before spending thousands on architects and quantity surveyors, but professionals won't give you numbers without paying them first. This catch-22 paralyses homeowners at the start of every extension project.
Think of our system as having a virtual builder and quantity surveyor working together in realtime with you. When you enter your project details, we break it down into all the steps involved in construction – from foundations to finishes.
How we calculate your estimate:
- We break your project into construction steps – foundations, oversite, walls, roofing, electrical, plumbing, etc.
- For each step, we use your dimensions and specifications to calculate accurate material quantities needed (concrete volume, brick counts, cable lengths, etc.)
- From quantities, we calculate labour hours and days required for each trade, based on our experience of running projects like this
- Our estimate tool offers multiple specification options (roof type, make open plan, large opening) – when you change an option, we instantly recalculate everything
- All costs include materials, labour, and sensible builder margins, informed by 20+ years of real UK construction projects
Most UK extensions fall within 15% of our estimates because we calculate from your actual dimensions and specifications, not generic averages. We track this continuously and adjust our methodology when patterns change.
Actual costs vary based on your specific requirements, site conditions, and builder chosen. Our role is to give you realistic expectations, not precise quotes.
Regional pricing adjustments
Why London extensions cost more than Manchester ones
Construction costs vary by location across the UK. Inner London projects cost approximately 20% more than the North West, with significant variations across all regions. These differences reflect real variations in local labour rates and material delivery costs.
How we calculate regional adjustments:
- Material rates: materials cost different amounts depending on where you are in the country
- Local labour rates: Tradespeople charge more in high-cost areas to cover their living expenses
For example, a 25m² extension in Manchester typically costs £55k-£70k, while the same project in Inner London runs £66k-£84k. These differences reflect real variations in local labour rates and material delivery costs.
Red flag:
When online calculators don't ask for your postcode, they're giving you misleading averages that could be 20-40% off your actual local costs.
Timeline calculation methodology
Understanding realistic project durations
Timeline estimation uses the same project steps data as cost calculations.
How we calculate timelines:
- We anayse the quantity of work in each construction step (calculated from your actual dimensions)
- We factor in the number of labourers typically required for each trade to complete the work efficiently
- Days are rounded up to the nearest week where applicable, grouped by related tasks (e.g., all groundwork together)
Our timelines assume you get planning approval first time, council processes applications promptly, and your builder can start when you need them to.
Important timeline considerations:
Actual timelines vary significantly based on weather conditions, planning delays, builder availability, and your own decision making speed. Our estimates give you a baseline, but build in contingency time for the inevitable unexpected delays.
What's included
What's in the estimate and what costs extra
Included:
- Materials and labour
- Professional fees (where applied)
- VAT at 20%
Not included:
- Contingency (add 10-15%)
- Furniture and appliances
- Landscaping
Why our independence matters
No commissions, no lead generation, no hidden agendas
Many platforms need to monetise through builder referrals and lead generation. While this works for their business model, it creates natural incentives that can influence which options they highlight.
We maintain genuine independence through our business model. We don't profit from which architect, builder, or professional you choose. We don't sell your contact details. We don't take commissions from referrals.
What this means for you:
- Our success is measured by estimate accuracy, not by converting you into a lead
- Our advice about when to hire professionals is genuinely about your best interests
- You can explore sample projects and see how our tool works before signing up
- We focus on equipping you with knowledge to make informed decisions, not matching you with partners who pay us
Common questions
Additional details about our methodology
Questions about our methodology?
We're happy to explain any aspect of how we calculate estimates. Get in touch if you'd like to discuss our methodology in more detail.