Comparison · Property & Landlord Finance · 2026
Buy-to-Let Mortgage vs Commercial Mortgage 2026: Financing HMOs and Portfolios
A standard Buy-to-Let mortgage works well for a single self-contained let, but larger HMOs, mixed-use property and growing portfolios often need specialist HMO, Multi-Unit Freehold Block or commercial financing instead. This guide compares the two routes, covering portfolio-landlord underwriting, HMO licensing, Section 24 and Ltd company structures for 2026/27.
TL;DR -- 30-Second Summary
- • Standard BTL suits single self-contained lets and usually has lower rates
- • Commercial/HMO mortgages are needed for larger HMOs (7+ bedrooms) or mixed-use property
- • 4+ mortgaged BTL properties makes you a portfolio landlord, stress-tested across the whole portfolio
- • Mandatory HMO licensing applies to 5+ unrelated occupants across 2+ households (since Oct 2018)
- • Ltd company structures avoid the Section 24 restriction but face higher mortgage rates and accountancy costs
Side-by-Side Comparison
| Feature | Standard Buy-to-Let mortgage | Commercial / specialist HMO mortgage |
|---|---|---|
| Typical property type | Single self-contained residential let | Large HMO (7+ bedrooms), MUFB, mixed-use |
| Affordability assessment | Whole-property market rent | Often per-room rental income |
| Typical rates | Generally lower | Generally higher |
| HMO licensing (5+ occupants, 2+ households) | Not usually applicable | Often required before completion |
| Portfolio landlord underwriting (4+ mortgaged BTLs) | Whole-portfolio stress test applies | Whole-portfolio stress test applies |
| Section 24 (individual ownership) | 20% tax credit only, applies regardless of mortgage type | |
| Ltd company ownership | Corporation tax (19%/25%), full interest deductible, no Section 24 | |
| Additional property SDLT surcharge | 5% on most additional residential purchases, incl. most HMOs | |
Worked Example: A 6-Bedroom HMO Purchase
A landlord already owns four mortgaged Buy-to-Let properties and is buying a sixth residential property to run as a licensable HMO with six unrelated tenants across three households, at a purchase price of GBP 300,000.
| Factor | Implication |
|---|---|
| Existing 4 mortgaged BTL properties | Already a portfolio landlord -- whole portfolio stress-tested |
| 6 unrelated occupants, 3 households | Mandatory HMO licence required (5+ occupants, 2+ households) |
| Mortgage type | Specialist HMO mortgage likely required, not standard BTL |
| Stamp duty surcharge on GBP 300,000 | 5% additional property surcharge applies on top of standard SDLT bands |
| Ownership structure choice | Ltd company avoids Section 24; higher mortgage rate, corporation tax instead |
This landlord faces three compounding factors at once: portfolio-wide underwriting because of the existing four properties, mandatory licensing because of the occupant and household count, and a mortgage type outside standard BTL criteria because the property is a larger HMO. Each factor is assessed independently by the lender, so meeting one does not remove the need to satisfy the others.
When a Standard Buy-to-Let Mortgage Wins
A standard BTL mortgage wins for a single self-contained let, a small portfolio under the four-property portfolio-landlord threshold, and any property that does not require an HMO licence. The lower rates, simpler underwriting and wider choice of mainstream lenders make it the more efficient route whenever a property genuinely fits standard criteria.
It remains the right choice even for experienced landlords who deliberately keep individual properties as self-contained lets rather than converting to HMOs, since the licensing and underwriting overhead of HMO financing only pays off with the higher rental income HMOs can generate.
When Commercial or Specialist HMO Financing Wins
Commercial or specialist HMO financing wins once a property genuinely does not fit standard BTL criteria, typically larger HMOs, mixed residential/commercial buildings, or Multi-Unit Freehold Blocks. The higher rental income from letting by the room can outweigh the higher interest rates and licensing overhead, particularly in strong HMO rental markets such as university towns and cities with high demand for shared housing.
It also becomes the practical choice for growing portfolio landlords who need lenders comfortable underwriting across a larger, more complex portfolio, since not every mainstream BTL lender competes seriously in that space.