The question every landlord asks before converting
You have found a house. Let to a family it might do £1,100 a month. Split it into five rooms and the same bricks could bring in £2,750. On paper the HMO looks like free money, so why doesn't every landlord convert?
Because the room premium is a gross-rent premium, and HMOs eat gross rent alive. Bills-included running costs, higher voids and licensing quietly claw back most of the gap. The only figure that decides anything is net yield: what actually lands in your account after the property is paid for, divided by the capital you tied up to buy and ready it.
So let me put both models on the same house and count properly.
The set-up: one house, two strategies
Here are the assumptions for a worked example (your local figures will differ, so treat these as illustration, not a promise):
- A mid-terrace house bought all-in for £210,000, including the 5% buy-to-let SDLT surcharge and legals.
- Single let: to a family at £1,100/month. Tenant pays council tax and all utilities.
- HMO: five lettable rooms at £550/room/month, bills included. The conversion (extra bathroom, fire doors, alarms, partition) costs £25,000, so capital employed rises to £235,000.
Same street, same building. The difference is entirely in how it earns.
Single let: fewer pounds in, far fewer pounds out
A family let is a quiet machine. One tenancy, one set of bills that isn't yours, and modest wear. Gross rent is £13,200 a year. Voids on a well-priced family home are low, so assume 3% (about eleven days). Your costs are insurance, repairs and the compliance drumbeat (gas safety, EPC, the odd bit of admin).
The rent is unglamorous. The cost base is skinny, and it is skinny because the tenant carries the bills.
HMO: big rent, big running costs
The HMO triples the top line to £33,000 if every room is full. It rarely is. Rooms turn over one at a time, so you carry more frequent voids and re-let gaps; 10% is a fair working assumption for a steady house, higher while you are settling it in.
Then you pay the bills. On a five-room house that means council tax on the whole property, gas, electric, water, broadband, the TV licence and communal cleaning. In this example:
- Council tax (whole house): £2,100
- Gas: £1,400
- Electric: £1,200
- Water: £600
- Broadband: £360
- TV licence: £169
- Communal cleaning and waste: £1,400
- Bills total: about £7,230
On top sit higher insurance, roughly double the maintenance (five occupants, shared kitchen and bathrooms), the HMO licence (amortised over its term) plus EICR, PAT and fire-alarm servicing, and management. HMOs are hands-on, so cost in management at 10% of collected rent even if you think you'll self-manage at first.
Side by side on the same house
| Line | Single let | HMO (5 rooms) |
|---|---|---|
| Capital employed | £210,000 | £235,000 |
| Gross annual rent | £13,200 | £33,000 |
| Voids | −£396 (3%) | −£3,300 (10%) |
| Bills paid by landlord | £0 | −£7,230 |
| Insurance | −£350 | −£700 |
| Repairs & maintenance | −£800 | −£2,000 |
| Compliance & licensing | −£270 | −£580 |
| Management (10% of rent) | £0 (self-managed) | −£2,970 |
| Net income | £11,384 | £16,220 |
| Gross yield | 6.3% | 14.0% |
| Net yield | 5.4% | 6.9% |
Does the premium survive? Just about
Look at gross yield and the HMO wins more than two to one: 14.0% against 6.3%. That is the number that makes people convert.
Look at net yield and the story changes. The gap collapses from 7.7 percentage points to about 1.5. The HMO still wins (6.9% versus 5.4%), so yes, the room premium survives, but a huge slice of it was never yours; it was always going to reach the gas supplier, the council and the cleaner.
Put in cash, the HMO earns roughly £4,800 more a year on £25,000 more capital and a great deal more work. That extra £4,800 is a real return on the conversion spend (around 19% on the £25k), which is attractive. But it is a world away from the "double the rent" headline, and it assumes you actually keep four or five rooms full.
What tips the balance either way
The example is a base case. A few real-world levers move it hard:
- Voids are the swing factor. Drop HMO voids to 5% and net yield jumps toward 8%. Let two rooms sit empty for two months and the premium can evaporate entirely. From 1 May 2026 all tenancies became periodic under the Renters' Rights Act 2025 (legislation.gov.uk), which suits room lets where tenants come and go, but it also means no fixed term to lean on.
- Energy costs land on the HMO landlord. When you pay the bills, an inefficient house hits your net yield, not the tenant's. The proposed minimum EPC band C for new tenancies by 2028 and all tenancies by 2030 (gov.uk) is a cost for both models, but only the HMO also pays the running energy bill in the meantime.
- Licensing and Article 4. HMO licence fees and any local Article 4 planning restriction can add cost and friction the single let never sees. Check the specific council before you assume a conversion is even allowed.
- Management is the hidden line. If you genuinely self-manage the HMO, add its net yield back toward 8%+, but be honest that five tenants is a part-time job, not a spreadsheet entry.
Run it on your own deal
The point is not that HMOs are worse. It is that you cannot judge them on gross rent, and you cannot compare the two strategies until both are on a net basis with bills, voids and management counted. Take the house you are actually looking at, put in your local room rates, your council tax band and a realistic void, and compare the net yields. The rental yield calculator will do the arithmetic so you can test whether the premium survives your numbers rather than a worked example.
If the HMO net yield only edges the single let by a point, ask whether the extra capital, admin and tenant management are worth it for your time and risk appetite. Sometimes they clearly are. Sometimes the quiet family let, at 5.4% net with almost no running costs and one tenant, is the better business.
This is general information, not tax or financial advice.
