Repayment vs Interest-Only Mortgages: Key Differences & Tax Implications

Choosing between a repayment mortgage and an interest-only mortgage is one of the most critical decisions when structuring a property loan. While repayment mortgages represent the default and safest route to homeownership, interest-only options offer lower monthly commitments, which can be highly attractive for property investors and corporate buyers. In this comprehensive guide, we compare the structures of both repayment methods, analyze their long-term costs, explain lender eligibility requirements, and discuss the tax rules for buy-to-let properties.

Comparative Structure: How Payments Differ

The difference in how monthly payments are applied has massive long-term implications:

• Repayment Mortgage: Each monthly payment is split between interest and principal. In the early years, the payment consists mostly of interest. In the later years, as the outstanding principal falls, more of each payment goes toward paying off the principal. The debt is guaranteed to reach £0 at the end of the term.
• Interest-Only Mortgage: Your monthly payment only covers the interest charged on the loan principal. Because the principal is never reduced, your monthly payment is significantly lower. However, at the end of the term, you must repay the full loan amount in one lump sum.

To run these calculations, use our Mortgage Calculator. If you are comparing limited company vs personal property tax structures, use our Property Limited Company vs Personal Tax Calculator.

Lender Eligibility Requirements for Interest-Only Mortgages

Due to the risk of borrowers reaching the end of their mortgage term without the funds to pay off the principal, the FCA strictly regulates interest-only residential lending. Lenders require:

• A Valid Repayment Vehicle: You must prove you have a reliable plan to repay the principal. Lenders accept ISAs, pension lump sums, investment portfolios, or a verified strategy of selling the property.
• Minimum Equity/Deposit: Residential interest-only loans often require a larger deposit, typically at least 25% to 40% (meaning a maximum loan-to-value of 60% to 75%).
• Minimum Income: Some lenders restrict interest-only residential deals to high earners (e.g. single income over £50,000 or joint over £75,000).

Tax Implications for Property Investors

For buy-to-let landlords, the structure of the mortgage impacts tax liabilities under Section 24. While individual landlords can no longer deduct mortgage interest from rental profits, limited companies can deduct mortgage interest as a business expense. Therefore, many landlords choose interest-only mortgages through limited company wrappers to keep their monthly operating costs low while maintaining maximum tax-deductible expenses.

References & Official Sources

This guide is formulated in accordance with the following official financial guidelines:

• FCA MCOB 11.6.41: Detailed rules governing interest-only residential mortgages and acceptable repayment vehicles.
• HMRC Income Tax (Trading and Other Income) Act 2005: Rules on property income finance cost tax relief limitations (Section 24).

Frequently Asked Questions: Repayment vs Interest-Only

Q: Can I switch from an interest-only mortgage to a repayment mortgage?
A: Yes. Most lenders allow you to switch to a repayment mortgage at any time. You can also make a partial switch (a part-and-part mortgage), where a portion of the loan is repayment and the rest is interest-only.

Q: Why are buy-to-let mortgages usually interest-only?
A: Interest-only minimizes monthly costs, maximizing net rental yield. Because property investors plan to sell the property or refinance at the end of the term to pay off the debt, they do not need to build equity through monthly repayments.