New investors lose money for predictable reasons. The property itself is rarely the problem. The numbers are.
Here are twelve mistakes that show up repeatedly, roughly in the order they occur.
1. Buying before understanding the numbers
The yield calculation is the foundation. Gross yield (annual rent divided by purchase price) tells you nothing useful by itself. Net yield (rental income minus all costs, divided by total capital invested including purchase costs) tells you whether the deal works.
A property yielding 7% gross might yield 3% net after mortgage payments, insurance, management fees, maintenance, void periods, and compliance costs. If 3% net on your capital does not justify the risk and hassle, the deal is wrong.
2. Overpaying for the first purchase
Excitement beats discipline. You find a property you like, someone else is viewing it, and you offer £5,000 above asking to "secure" it. That £5,000 is gone. Check Land Registry sold prices for comparable properties. If the asking price exceeds recent comparables, negotiate or walk away.
3. Buying in the wrong area
Investors who buy near their own home because it feels familiar often end up with a property in an area where the rental demand, tenant profile, or yield does not support the strategy. Research the local rental market before choosing the area. Average rents, void periods, tenant demand, and local employment all matter more than proximity to your house.
4. Not using a specialist broker
Going to your high-street bank for a BTL mortgage limits you to one lender's products and criteria. A specialist BTL broker has access to the whole market, including lenders that do not accept direct applications. The broker fee (£300 to £500) pays for itself if they find a lower rate or a lender whose criteria fit your situation.
5. Underestimating running costs
New investors budget for the mortgage payment and nothing else. The real cost list: mortgage interest, insurance, letting agent fees (8-12% of rent), void periods (budget 4-8 weeks per year), maintenance and repairs (budget 10-15% of annual rent), compliance costs (gas safety, EICR, EPC, alarms), ground rent and service charges (leasehold), and accountancy.
6. Ignoring void periods
A property sitting empty for six weeks costs you six weeks of mortgage payments with no income to cover them. Budget for voids in your cash flow model. Reducing voids starts with buying in high-demand areas, pricing rent fairly, and maintaining the property so tenants stay longer.
7. Skipping tenant referencing
A bad tenant costs more than a void. Rent arrears, property damage, and the time and legal cost of eviction proceedings can wipe out a year's profit. Proper referencing (credit check, employer reference, previous landlord reference, affordability check) costs £20 to £50 per applicant and is the cheapest risk management you can buy.
8. Not having a cash reserve
A boiler breaks in December. A tenant moves out unexpectedly. A leak damages the ceiling. If you cannot cover a £2,000 emergency repair from savings, you end up borrowing at expensive rates or deferring the repair (which makes it worse and may breach your legal obligations). Keep a cash reserve of at least £3,000 to £5,000 per property.
9. Over-leveraging
Buying four properties in two years using maximum leverage across all of them leaves you vulnerable to any single shock: a rent void, a rate increase, or a market correction. If one property underperforms and you have no reserves, the pressure spreads to the others. Build slowly and ensure each property is cash-flow positive before acquiring the next.
10. Assuming prices only go up
UK house prices have risen over the long term, but there have been periods of flat or falling prices (2008-2013 being the most recent sustained decline). Buying at the top of a local cycle with maximum leverage means any price fall erodes your equity disproportionately. If you need to sell during a downturn, you may sell at a loss.
11. Ignoring tax planning
Buying in your personal name when you are a higher-rate taxpayer means Section 24 restricts your mortgage interest deduction. A limited company structure can reduce the tax burden, but it needs to be set up before you buy, not after. Tax advice at the start costs less than restructuring later.
12. Buying on emotion
The property "feels right." It has a nice garden. You would live there. None of this matters for a BTL investment. The only questions are: does the rent cover the costs with margin, is the area in demand, and can you exit at a reasonable price if you need to?
If the spreadsheet says no, the property is wrong. No amount of kerb appeal changes the maths.
Sources
- HM Land Registry, "UK House Price Index reports". https://www.gov.uk/government/collections/uk-house-price-index-reports [Accessed 6 May 2026]