House Extension Cost Calculator UK (2023)

Our House Extension Cost Calculator is designed to provide you with a quick and convenient way to estimate the cost of your house extension project.

Are you planning to extend your house and curious about the estimated cost?

Adding an extension to your house is an exciting endeavor that can significantly enhance your living space and increase the value of your property.

However, determining the cost of an extension on your house can be challenging, considering various factors such as size, materials, labor, and location.

House Extension Cost Calculator

House Extension Cost Calculator

House Extension Cost Calculator

Estimated Extension Cost:

With our calculator, you can get an estimated cost based on your extension size and the chosen cost level.

The cost level represents the average cost per square meter for the extension, taking into account factors like materials, finishes, and labor costs. You have the option to select from three cost levels: high, average, or lower, depending on your preferences and budget.

extension cost calculator

To use the House Extension Cost Calculator, simply enter the size of your extension in square meters and select the cost level that best matches your requirements. Click the “Calculate” button, and the calculator will provide you with an estimated cost for your house extension project.

Please note that the calculated cost is an approximation and serves as a general guide.

It’s essential to consult with professionals and obtain detailed quotes from builders, architects, or contractors to get a more accurate understanding of the expenses involved in your specific project.

Whether you’re planning a small extension or a significant expansion, our House Extension Cost Calculator can help you make informed decisions and plan your budget effectively.

Get started with your house extension project today by using our House Extension Cost Calculator. Happy calculating!


Calculating the cost of a house extension can vary depending on several factors, including the size, complexity, location, materials used, and any specific requirements or customizations. Here are some general guidelines for estimating the cost of a house extension in the UK:

Size of the extension: Determine the total floor area of the extension you plan to build. Multiply the floor area by the average cost per square meter to get an approximate cost. For example, if you want to build a 30 m2 extension and the average cost is £2,000 per m2, the estimated cost would be £60,000 (30 m2 x £2,000/m2).

How much does a house extension cost per m2 UK?

Cost per square meter (m2): A common method is to calculate the cost based on the average cost per square meter. In the UK, the average cost for a basic extension can range from £1,500 to £3,000 per square meter. However, this is a broad estimate, and the actual cost can vary significantly.

Additional factors

Keep in mind that the cost per m2 is a rough estimate and does not consider other factors such as site conditions, architectural design, complexity of the project, quality of materials, interior finishes, plumbing, electrical work, and any necessary planning permission or building regulation fees. These factors can significantly impact the overall cost.

Obtain quotes

It is highly recommended to consult with several contractors or builders who specialize in house extensions. They can assess your specific requirements, inspect the site, and provide you with accurate quotes based on your project’s scope and specifications.

Remember that the costs mentioned here are rough estimates, and prices can vary greatly depending on the region, market conditions, and individual project requirements. It’s always advisable to consult professionals and obtain multiple quotes to get a more accurate idea of the cost for your specific house extension project.

How long does a house extension typically take to complete?

The duration of a house extension project depends on various factors such as the size and complexity of the extension, any required planning permissions, weather conditions, and the availability of materials and contractors. On average, a straightforward house extension can take anywhere from a few months to a year to complete.

How can I finance my house extension?

Financing options for a house extension include personal savings, remortgaging your property, taking out a home improvement loan, or utilizing a specialist construction loan. Additionally, you may explore government-backed schemes or grants available for certain types of extensions. It is recommended to speak with a financial advisor or mortgage broker to assess the best financing option for your circumstances.

What factors can impact the cost of a house extension?

Several factors can influence the cost of a house extension. These include the size of the extension, the quality of materials and finishes, the need for additional structural work, plumbing and electrical requirements, architectural design complexity, and any necessary planning permission or building regulation fees. It’s essential to consider these factors when estimating the cost of your house extension project.

Are there any additional costs to consider when planning a house extension?

Yes, there are several additional costs to consider beyond the construction expenses. These may include architect or designer fees, structural engineer fees, planning application fees, building regulation fees, professional survey costs, VAT (Value Added Tax), and any expenses related to connecting utilities to the new extension. It’s important to factor in these additional costs when budgeting for your house extension.

Remember, the answers provided here are general in nature and may not apply to every specific situation. It is always recommended to seek professional advice tailored to your unique circumstances when considering a house extension.


Our House Extension Cost Calculator offers a valuable tool to estimate the cost of your house extension project. By providing the size of your extension and selecting a cost level, you can quickly obtain an approximate cost based on your preferences and budget.

While the calculator provides a helpful starting point, it’s important to remember that the estimated cost is just an approximation. Several variables, such as the complexity of the design, specific materials chosen, location factors, and unforeseen circumstances, can impact the overall cost of your house extension.

To ensure the accuracy of your budget and to receive more detailed and tailored cost estimates, we highly recommend consulting with professionals, such as architects, builders, or contractors. They can provide expert guidance, assess your specific requirements, and offer precise quotations based on your unique project specifications.

Remember that careful planning, thorough research, and open communication with professionals are key to a successful house extension project. Consider obtaining multiple quotes, reviewing previous work by contractors, and discussing your ideas and budget with experienced professionals to make informed decisions.

We hope that our House Extension Cost Calculator has provided you with valuable insights and helped you in the initial stages of estimating your house extension expenses. Good luck with your project, and may your house extension journey be exciting, fulfilling, and within your budget!

Author Profile

Mark Cullen
Mark Cullen
I have many qualifications and certificates in construction, such as City & Guilds, CPCS and CITB. These are the highest standards of training and competence in the industry. Whether you need help with plumbing, carpentry, bricklaying or any other trade, I’m here to help you succeed.