How do buy-to-let mortgages work for portfolio landlords?
A buy-to-let mortgage is a loan secured on a property bought to rent out. Lenders size it mainly on the rent, testing that rent covers the interest by a set margin at a stressed rate. Landlords with four or more mortgaged rental properties are treated as portfolio landlords and face fuller checks.
Read more in our guide: Mortgage debt and your portfolio
Key buy-to-let lending terms
| Term | Typical position |
|---|---|
| Loan to value | Commonly up to 75%, sometimes 80% |
| Repayment type | Mostly interest only |
| Rent test | Often 125% (company or basic rate) or 145% (higher rate) of interest |
| Portfolio landlord | Four or more mortgaged buy-to-let properties |
| Regulation | Usually unregulated; consumer buy-to-let has separate rules |
| Early repayment | Fixed rates usually carry early repayment charges |
How lenders size the loan
A residential mortgage is based on income. A buy-to-let mortgage is based mainly on the rent. Lenders apply an interest cover ratio test at a stressed interest rate, then cap the loan at a maximum loan to value. Whichever limit is lower decides how much you can borrow.
The Bank of England's Prudential Regulation Authority sets minimum underwriting standards for these loans, including stress testing and extra checks on portfolio landlords.
Portfolio landlords
Once you have four or more mortgaged buy-to-let properties, lenders look at the whole portfolio, not just the property being financed. Expect to provide a property schedule, business plan, cash flow forecast and sometimes accounts. A weak property elsewhere in the portfolio can affect a new application.
Mortgages and tax
For individual landlords, Section 24 restricts mortgage interest relief to a basic rate tax credit, which is why higher-rate landlords face a tougher 145% rent test. From April 2027 the credit is due to be given at 22%, in line with the new property income basic rate. Companies deduct interest in full, which is one reason many landlords now borrow through a limited company.
What happens when you sell
The mortgage is repaid from the sale proceeds on completion. Your solicitor obtains a redemption statement showing the balance, interest to the completion date and any early repayment charge. See mortgage redemption for the detail. Some products are portable to a new property, but most buy-to-let fixes are simply repaid.
Official Sources and Further Reading
- Bank of England: underwriting standards for buy-to-let mortgage contracts (SS13/16)
- MoneyHelper: buy-to-let mortgages
General information for landlords in England, checked against official sources in October 2026. It is not tax, legal or financial advice: speak to a qualified accountant or solicitor about your own circumstances.
Frequently Asked Questions
A buy-to-let mortgage is a loan secured on a property bought to rent out. Lenders size it mainly on the rent, testing that rent covers the interest by a set margin at a stressed rate. Landlords with four or more mortgaged rental properties are treated as portfolio landlords and face fuller checks.
Yes. The buyer takes on the tenancy and your mortgage is repaid from the proceeds at completion. You do not need the tenant to leave.
A buy-to-let loan to someone not letting as a business, such as an inherited home or a former home that is now let. It has its own regulatory protections.
Because the risk sits across many properties. PRA rules require lenders to assess the whole portfolio's rent, borrowing and cash flow.
Thinking About Selling Your Portfolio?
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