What Is an HMO? The Full Definition, Licensing and Fines

The legal definition — Housing Act 2004, section 254

The statutory definition sits in section 254 of the Housing Act 2004. Its main route, the “standard test,” describes a building that “consists of one or more units of living accommodation not consisting of a self-contained flat” where “the living accommodation is occupied by persons who do not form a single household” as their only or main residence, “rents are payable or other consideration is to be provided in respect of” at least one occupier's stay, and — the condition that actually makes it an HMO rather than just a shared house — “two or more of the households who occupy the living accommodation share one or more basic amenities or the living accommodation is lacking in one or more basic amenities.” Section 254(8) defines a basic amenity as a toilet, personal washing facilities, or cooking facilities. Two other, less common routes to HMO status exist in the same section: the self-contained flat test and the converted building test, plus a council declaration under section 255 and converted blocks of flats under section 257.

HMO vs “large HMO” — the two different thresholds

It's worth keeping two separate numbers apart, because most of the online confusion about HMOs comes from merging them. A property becomes an HMO once 3 or more tenants, forming more than 1 household, share toilet, bathroom or kitchen facilities — the section 254 test above. It only becomes a large HMO requiring a mandatory licence at a higher bar: gov.uk states you must have a licence if “it is rented to 5 or more people who form more than 1 household,” “some or all tenants share toilet, bathroom or kitchen facilities,” and “at least 1 tenant pays rent” (or has it paid for them). A 3- or 4-tenant shared house is an HMO in law, with the usual landlord safety duties, but it doesn't trigger the national licensing requirement on its own.

Mandatory licensing since 1 October 2018 — the storey rule was removed

Before October 2018, mandatory HMO licensing in England only caught properties of 3 or more storeys. The Licensing of Houses in Multiple Occupation (Prescribed Description) (England) Order 2018 changed that: it came into force on 1 October 2018 and prescribes a licensable HMO as one that “is occupied by five or more persons,” “is occupied by persons living in two or more separate households,” and meets one of the section 254 residential tests — with no minimum number of storeys at all. That single change is why a two-storey house with 5 unrelated sharers can need a licence today when the same house wouldn't have before 2018.

Additional and selective licensing — smaller HMOs, or every rental in an area

The 5-person national threshold is a floor, not a ceiling. Councils can run their own additional licensing schemes that extend HMO licensing down to smaller HMOs in a defined area, and selective licensing schemes that require a licence for any private rented property in a designated area — HMO or not — usually to tackle poor conditions or anti-social behaviour locally. These are set, published and administered council by council, not nationally, so a property that sits below the 5-person threshold can still need a licence depending purely on its postcode. See our HMO licensing by council hub and the licence fees by council table for the councils where we've verified the scheme and the fee directly from the council's own page.

The fine, the civil penalty, and rent repayment orders

Running a large HMO without the licence it needs carries three separate routes of financial exposure. First, prosecution: gov.uk states plainly, “You could get an unlimited fine for renting out an unlicensed HMO.” Second, a civil penalty as an alternative to prosecution under section 249A of the Housing Act 2004 — MHCLG's own guidance confirms the maximum was £30,000 for offences up to 30 April 2026, and a statutory instrument raised it to £40,000 for offences committed on or after 1 May 2026, alongside the wider Renters' Rights Act 2025 enforcement changes. Third, a rent repayment order: gov.uk's tenant guidance on RROs states an order “allows you to receive up to two years' worth of rent from a landlord who has committed certain housing related offences,” and “you can apply for an RRO at any point within two years of your landlord committing an offence” — letting an unlicensed HMO is one of the listed qualifying offences.

Planning permission — C4 use class and Article 4 directions

Separately from licensing, converting a house into a small HMO can be a planning matter. The Town and Country Planning (Use Classes) Order sets Class C4 — Small Houses in multiple occupation as its own use class, distinct from an ordinary dwelling (C3). Nationally, a change from C3 to C4 is normally permitted development and doesn't need a fresh planning application on its own — but a local Article 4 direction can remove that right. gov.uk's planning guidance defines one as a direction that “enables the Secretary of State or the local planning authority to withdraw specified permitted development rights across a defined area.” Councils with HMO pressure commonly use an Article 4 direction to withdraw the C3-to-C4 permitted development right, which means full planning permission is needed for a conversion in that area even though it wouldn't be needed nationally. Check your council's own Article 4 map before assuming a conversion is permitted development.

Tax: licence fees and compliance costs are deductible

An HMO licence fee, and the certificates an HMO licence requires (an annual gas safety certificate, electrical safety certificates), are normal running costs of the letting business, not capital costs of the property — deductible from rental income in the year you pay them. See the full allowable expenses list and our gas safety certificate cost page, and run your numbers through the rental income tax calculator.

legislation.gov.uk: Housing Act 2004 s.254 · gov.uk: house in multiple occupation licence · SI 2018/221, in force 1 Oct 2018 · gov.uk: rent repayment orders, guidance for tenants · gov.uk: civil penalties under the Renters’ Rights Act 2025, all read verbatim 11 Sep 2026. No national HMO licence fee figure is published — each council sets its own; see the licence fees by council table for the rows we've verified.