Mixed Use Property: How to Split Expenses for Tax Relief

What Is a Mixed Use Property?

A mixed use property is one used for more than one purpose, most commonly a property you live in but also rent out in part, or a property you let for part of the year and use personally for the rest. As a sole trader or freelancer who earns rental income, you must only claim tax relief on the portion of expenses that relates to the lettings activity. HMRC is clear: personal use costs are not deductible against rental income.

The Two Main Apportionment Methods

HMRC does not prescribe a single formula, but it expects your method to be fair and consistent. The two most commonly accepted approaches are:

• Floor area apportionment: Divide the floor area used for letting by the total floor area of the property. For example, if a lodger occupies one room that is 15 square metres in a 90 square metre home, 16.7% of shared expenses can be attributed to the letting.
• Time apportionment: Used when the same space is let for only part of the year. If you let a holiday cottage for 20 weeks of the 52-week year, roughly 38.5% of annual expenses are attributable to the rental period.

Where both space and time are relevant, you may need to combine these methods. For instance, a room let for part of the year requires a floor area fraction applied first, then a time fraction applied to the result.

Which Expenses Can You Apportion?

Only shared or joint expenses need apportioning. Expenses that relate exclusively to the let portion, such as a replacement bed or a letting agent fee, are fully deductible. Common expenses that require apportionment include:

• Mortgage interest (note: only the finance cost restriction rules apply for residential lettings since April 2017, giving basic rate tax relief only)
• Buildings and contents insurance
li>Council tax (if paid during a void period where you personally occupy the property)
• Utility bills such as gas, electricity, and broadband
• Cleaning and maintenance costs for shared areas
• General repairs to the fabric of the building

Rent a Room Relief: A Simpler Alternative

If you rent a furnished room in your own home, you may qualify for the Rent a Room scheme. This gives you up to £7,500 per tax year of gross rental income completely tax free (or £3,750 if you share the allowance with another person). If your gross rental receipts are below this threshold, you have no tax to pay and no apportionment is needed. Above the threshold, you can opt out and use the normal expense apportionment method instead, which may be more beneficial if your actual expenses are high.

Record Keeping Is Essential

HMRC can challenge your apportionment if you cannot demonstrate the basis you used. Keep the following records:

• Floor plans or measured drawings showing room sizes
• A letting diary or booking records showing dates the property was let
• Receipts and invoices for all expenses claimed
• Your written calculation showing how you arrived at the apportioned figures

Store these records for at least five years and ten months after the end of the tax year to which they relate, in line with HMRC requirements for self-assessment taxpayers.

Common Mistakes to Avoid

Overclaiming is the most frequent error HMRC sees in rental accounts. Do not claim 100% of your mortgage interest, council tax, or insurance simply because the property generates some rental income. Equally, do not guess your apportionment and apply a different percentage each year without good reason. Consistency and a documented methodology are your best defence in the event of an enquiry.

If your situation is complex, for example a large property with multiple let rooms and seasonal personal use, consider speaking to a qualified tax adviser to ensure your apportionment is robust and defensible.