Construction Industry Scheme Mortgages CIS: Essential Guide

If you work in the construction industry as a subcontractor under the Construction Industry Scheme (CIS), getting a mortgage can feel like an uphill battle. Many high street lenders struggle to assess CIS income properly, often treating you as self-employed and only considering your net profit after tax — which significantly underestimates what you actually earn. The good news is that a growing number of specialist lenders now understand CIS income and can offer competitive mortgage deals based on your gross contract income.

In this guide, we explain exactly how CIS mortgages work, which lenders accept CIS income, what documents you need, and how to maximise your borrowing power.

What Is the Construction Industry Scheme?

The Construction Industry Scheme is an HMRC tax framework that applies to contractors and subcontractors working in the UK construction sector. Under CIS, main contractors deduct tax at source from subcontractors’ payments before passing those deductions to HMRC. The standard deduction rate is 20%, though unregistered subcontractors face a higher 30% deduction.

CIS exists to ensure tax compliance in the construction industry, but it creates a unique challenge when it comes to mortgages. Because tax is deducted at source by the contractor, CIS subcontractors are in a position somewhere between employed and self-employed. Your income is relatively predictable and verifiable — much like an employed person — but most lenders still classify you as self-employed and assess your income accordingly.

This classification matters because self-employed mortgage assessments typically rely on SA302 tax calculations or certified accounts, which show your net profit after allowable expenses. For CIS workers who claim significant expenses such as tools, materials, travel, and vehicle costs, this net figure can be substantially lower than your actual gross earnings.

How Do Lenders Assess CIS Income?

There are broadly two approaches lenders take when assessing CIS income for mortgage purposes.

Standard self-employed assessment — Most high street lenders treat CIS subcontractors the same as any other self-employed applicant. They require two to three years of SA302 tax calculations or accountant-prepared accounts and base your borrowing on the average net profit over those years. If you claim heavy expenses, this approach can dramatically reduce how much you can borrow.

Gross income assessment — A smaller number of specialist lenders recognise that CIS income is taxed at source and therefore more verifiable than typical self-employed income. These lenders assess your mortgage based on your gross contract income before expenses are deducted, using your CIS payment and deduction statements as evidence. This approach can significantly increase your borrowing capacity.

For example, if your gross CIS income is £50,000 per year but your net profit after expenses is £32,000, a standard lender might offer you a mortgage based on £32,000 (roughly £144,000 at 4.5x income). A specialist CIS lender using gross income could base your mortgage on £50,000 (roughly £225,000 at 4.5x), a difference of over £80,000 in borrowing power.

Which Documents Do You Need for a CIS Mortgage?

The exact documentation varies by lender, but you should be prepared to provide the following when applying for a CIS mortgage.

• CIS payment and deduction statements — these are the monthly statements from your contractor showing your gross pay and tax deducted. Most lenders want to see at least 3 to 12 months’ worth.
• SA302 tax calculations — your Self Assessment tax computation from HMRC, usually covering one or two years.
• Tax year overview — the corresponding HMRC document confirming your tax position for each year.
• Bank statements — typically three to six months of personal and/or business bank statements showing CIS income being deposited.
• Contracts or subcontractor agreements — evidence of your ongoing work arrangements.
• ID and proof of address — standard identification documents such as passport and utility bills.
• Deposit proof — evidence of your deposit funds and their source.

If you are registered for CIS with HMRC and have a UTR (Unique Taxpayer Reference) number, this helps verify your status. Some lenders also accept verification directly through HMRC’s CIS online system.

How to Maximise Your Borrowing as a CIS Worker

There are several practical steps you can take to improve your chances of securing the best possible CIS mortgage deal.

Use a specialist broker — this is arguably the single most important step. A broker who understands CIS mortgages, like the team at Option Finance, will know exactly which lenders accept CIS income on a gross basis and which products offer the best rates for your circumstances. Applying to the wrong lender can waste time and leave unnecessary credit search footprints on your file.

Keep your CIS statements organised — lenders need clear, complete records of your CIS income. Make sure you receive and file your monthly CIS payment and deduction statements from every contractor you work with. Gaps or missing statements can delay your application.

Consider your expense claims carefully — while it is perfectly legitimate to claim allowable business expenses on your tax return, be aware that higher expenses reduce your net profit. If you are planning to apply for a mortgage, it may be worth discussing with your accountant whether there are expenses you could defer or whether a gross-income lender would be more suitable for your situation.

Maintain a clean credit record — regardless of how you earn your income, lenders will check your credit history. Pay bills on time, keep credit card balances low, and avoid making multiple credit applications in the months leading up to your mortgage application. If you have had credit issues in the past, read our guide on adverse credit mortgages for specialist options.

Save the largest deposit you can — a larger deposit reduces the lender’s risk and gives you access to better interest rates. Aim for at least 10% if possible, though some CIS-friendly lenders accept deposits as low as 5%.

CIS Mortgages for First-Time Buyers

If you are a CIS subcontractor buying your first home, you face the same challenges as other CIS workers with the added complexity of having no property-owning track record. However, many lenders that accept CIS income are also open to first-time buyer applications.

Key considerations for CIS first-time buyers include understanding how much you can borrow based on your gross or net income, taking advantage of government schemes such as the Lifetime ISA, and ensuring your credit profile is as strong as possible before applying.

You can use our self-employed mortgage calculator to get an initial estimate of how much you might be able to borrow based on your CIS income. For a broader view of monthly repayments, try our mortgage calculator or check what you can realistically afford with our affordability calculator.

If you are new to the property market, our guide to first-time buyer mortgages covers the full process from deposit to completion. For a complete overview, read our ultimate UK first-time buyer mortgage guide.

CIS Remortgages and Buy-to-Let

CIS income is not just relevant for purchase mortgages. If you already own a property and want to remortgage to a better deal, your CIS income will need to pass the new lender’s affordability assessment. Using a specialist lender who assesses gross CIS income can make this process much smoother, particularly if your current deal is coming to an end and you want to avoid reverting to your lender’s standard variable rate.

CIS subcontractors also sometimes look to invest in property. Buy-to-let mortgages have their own set of criteria, but your personal income still needs to meet minimum thresholds for most lenders. Again, having a broker who understands how CIS income interacts with buy-to-let affordability rules is invaluable.

CIS Mortgage Interest Rates and Deposits

A frequent concern among CIS subcontractors is whether they will face higher interest rates or need larger deposits than employed borrowers. The answer depends on several factors, but CIS workers are often pleasantly surprised by what is available.

Interest rates — lenders who specialise in CIS income understand that it is taxed at source, making it one of the more verifiable forms of self-employed income. As a result, their rates for CIS workers with clean credit and reasonable deposits are often very competitive — sometimes matching or coming close to the rates available to salaried applicants. The key factors affecting your rate are your loan-to-value ratio (the proportion of the property’s value you are borrowing), your credit history, and the specific lender’s pricing at the time you apply.

Deposit requirements — most CIS-friendly lenders accept deposits from 5% to 10%, with the best rates reserved for deposits of 15% or more. If you can stretch your deposit to a higher threshold — from 10% to 15%, or from 15% to 20% — you will typically unlock a better interest rate tier, which can save you thousands of pounds over the course of your mortgage term.

Arrangement fees — some specialist lenders charge arrangement fees (also called product fees) which can be added to the mortgage or paid upfront. When comparing deals, always consider the total cost of the mortgage over the initial rate period, including fees, not just the headline interest rate. Your broker can run these calculations for you so you can compare like with like.

Valuation and legal fees — these are standard costs that apply to all mortgage applications, not specific to CIS workers. Some lender deals include free valuations or cashback contributions towards legal fees, which can reduce your upfront costs.

Common Questions About CIS Mortgages

Can I get a CIS mortgage with less than two years’ trading history? — Yes. Some specialist lenders accept CIS subcontractors with as little as 6 to 12 months of CIS statements. This is significantly more flexible than the standard self-employed requirement of two or three years’ accounts. Read our guide on self-employed mortgages for more on income requirements.

Do CIS deductions count as tax paid? — Yes. CIS deductions are advance payments of your income tax. When you complete your Self Assessment tax return, HMRC will offset your CIS deductions against your tax liability. If you have overpaid, you can claim a refund.

Can I use CIS income alongside employed income? — Absolutely. If you have both CIS income and income from PAYE employment, many lenders will consider both income streams when calculating your borrowing capacity. This is similar to how lenders handle self-employed with complex income from multiple sources.

What if I have gaps in my CIS work? — Gaps can be a concern for lenders, as they may suggest inconsistent income. If you have seasonal work patterns that are normal for your trade, a specialist broker can present this to lenders in the best light. Consistent bank statements showing regular income deposits help support your case.

Are CIS mortgage rates higher than standard rates? — Not necessarily. If you use a lender that fully understands CIS income and you have a clean credit record with a reasonable deposit, you can access rates comparable to those available to employed borrowers. The key is finding the right lender.

How Option Finance Can Help

Navigating the CIS mortgage market without expert guidance can lead to rejected applications, wasted time, and unnecessary credit searches that damage your file. At Option Finance, we work with a wide panel of lenders, including those who specialise in CIS and construction industry income. Our advisers understand the nuances of CIS payment structures and know exactly how to present your income to maximise your borrowing.

Whether you are a first-time buyer, looking to move home, remortgaging, or exploring buy-to-let opportunities, we can match you with the right lender for your CIS income and circumstances. We handle the paperwork, liaise with lenders on your behalf, and guide you through every step of the process.

Ready to explore your CIS mortgage options? Get in touch with our team today for a free, no-obligation consultation. We will review your income, discuss your goals, and find the best mortgage deal available to you.