Reviewed and updated: 17 October 2026. Original archive publication date retained.
An HMO calculator can organise an appraisal, but it cannot establish the rent a property will achieve or whether the proposed occupation is lawful. Start by checking what the tool calls yield, profit and cash flow. They are different measures.
Gross yield is only one view
Gross rental yield expresses annual rent as a percentage of the property value or purchase price used in the calculation. Keep that denominator explicit. A gross measure does not deduct the costs of operating the letting.
The Mortgage Works describes its rental-yield calculator as illustrative and notes that it does not show capital gains or property-maintenance costs. Similar limitations should be checked for any tool.
Build a separate cost schedule
For a room-based letting, record the assumed rent and occupied period for each room. Then identify expenses such as utilities where included, management, cleaning, repairs and any applicable licensing costs. Financing and tax require their own treatment.
Avoid counting a deposit as income or assuming every room produces rent throughout the year. Test what happens when a room is empty or a repair is needed.
A useful output keeps the evidence and assumptions alongside the result. It should be possible to change an input and understand why the figure moves. No percentage alone demonstrates that an HMO is suitable, affordable or capable of delivering the projected return.