Switching between a residential and buy-to-let mortgage

A residential mortgage is assessed on the borrower's income and is for a home they live in. A buy-to-let mortgage is assessed mainly on the rent and is for a property let to tenants. Buy-to-let usually needs a larger deposit, is often interest-only and is mostly unregulated, while residential mortgages are regulated.

Pricing differs too. Buy-to-let products tend to carry higher rates and fees than residential products at the same loan-to-value, reflecting the different risk, as explained on the buy-to-let mortgage rates page. The tax treatment of the property also changes once it is let, including on mortgage interest and on any gain when it is sold (GOV.UK, restricting finance cost relief for individual landlords, accessed 20 Oct 2026).

There are two ways to let a home that has a residential mortgage. The first is to ask the current lender for consent to let, which allows letting for a period on the existing mortgage, sometimes with a fee or higher rate. The second is to remortgage onto a buy-to-let mortgage with the current lender or a new one.

Consent to let is usually granted for a set time, such as when a move is expected to be temporary, and lenders do not have to agree. Remortgaging to buy-to-let is the usual route when the letting will be long-term. The new loan has to pass the lender's rent test, and any early repayment charge on the residential deal may apply.

Letting without consent breaches the mortgage terms and can also invalidate home insurance, so the switch or consent should be in place before a tenant moves in.

When the owner is moving to a new home and keeping the old one as a rental, the switch is part of a let to buy arrangement. The old home moves to a buy-to-let mortgage, often raising equity for the new deposit, and the new home is bought with a residential mortgage. Both are usually arranged to complete together.

Buying the new home while keeping the old one usually means the higher rates of Stamp Duty Land Tax for additional property apply (GOV.UK, Stamp Duty Land Tax: higher rates for additional properties, accessed 20 Oct 2026). How the two mortgages work together is explained on the page about let to buy mortgages.

Moving into a property that has a buy-to-let mortgage means switching to a residential mortgage, because buy-to-let terms do not allow the owner to live there. The switch is a remortgage, assessed on the borrower's income rather than the rent, and it is usually arranged once the tenancy has ended.

Residential lenders apply full affordability checks under FCA rules, so the borrower's income and outgoings decide how much can be borrowed. An early repayment charge on the buy-to-let deal may apply if the switch happens before the deal ends, and some lenders allow a product switch to residential with the same lender.

Some lettings sit between the two types. Letting to close family is usually a regulated mortgage contract, and accidental landlords who let a former home they could not sell may be on consumer buy-to-let, which has its own protections (FCA Handbook PERG 4.4, accessed 20 Oct 2026). Lenders decide which applies.

The rules that apply to each type of buy-to-let, including the rent test and lender criteria, are set out in the guide on how buy-to-let mortgages work. Comparing the cost of consent to let, a product switch and a full remortgage helps when deciding how to make the change.