I spent a long time using rental yield as my primary lens for evaluating property investments, and it took a few years of real numbers to understand how much the metric was leaving out.
Rental yield — the annual rent as a percentage of property value — is the number most property investors use to evaluate a buy-to-let opportunity. It is also one of the most incomplete metrics available. Gross yield takes no account of finance costs, void periods, maintenance, management fees, insurance, or tax. A property yielding 6% gross can easily produce negative cash flow once all costs are included. The only number that matters is what actually arrives in your account after everything else has been paid.
What Rental Yield Leaves Out
Gross rental yield is calculated as annual rent divided by property purchase price, expressed as a percentage. On a £200,000 property renting for £900/month: (£900 × 12) / £200,000 = 5.4% gross yield. This figure is used in property listings, investment comparisons, and landlord marketing. It omits almost everything that determines whether the investment is profitable.
Net yield adjusts for some costs — typically management fees and maintenance — but still excludes mortgage interest, which is by far the largest cost for leveraged investors. Even net yield fails to answer the question that matters: after all costs including finance, what is the actual cash return on the capital invested?
Return on investment (ROI) for a leveraged buy-to-let is calculated on the cash invested — typically the deposit plus transaction costs — not on the total property value. A property that appears to offer modest yield at full value can produce significantly higher or lower ROI depending on leverage, interest rate, and actual net income.
Mortgage Costs, Repairs, and Void Periods
For a landlord with a 75% LTV buy-to-let mortgage on a £200,000 property at 5.5% interest-only rate: monthly mortgage interest = £200,000 × 0.75 × 5.5% / 12 = £687.50. On rent of £900/month, the mortgage alone takes 76% of rental income before any other cost is considered.
Maintenance and repairs: budget 1% of property value per year as a minimum provision. On a £200,000 property: £2,000/year, or £167/month. Void periods — time between tenancies when no rent is received — average 2 to 4 weeks per year across the UK market. At £900/month, one month void per year reduces effective annual rent from £10,800 to £9,900. Insurance: landlord insurance typically costs £150 to £400/year depending on property and location. Safety certificates: gas safety, electrical condition report, EPC — approximately £200 to £400/year across required renewals.
Tax and Management Fees
Rental income is taxed as income at your marginal rate. Since 2020, mortgage interest relief for individual landlords has been restricted to the basic rate (20%) regardless of actual income tax rate — meaning higher-rate taxpayers pay tax on rental income gross of mortgage interest but only receive 20% relief. This significantly worsened the post-tax economics of leveraged buy-to-let for higher-rate taxpayers and is a central driver of the calculation that determines whether leveraged buy-to-let is still profitable for any individual investor.
Letting agent management fees: typically 8% to 15% of monthly rent for full management. On £900/month at 10%: £90/month, £1,080/year. Tenant find only: typically one month's rent (£900) when a new tenant is required.
Cash Flow vs Return on Investment
Monthly cash flow on the example property: rent £900, minus mortgage £688, minus maintenance provision £167, minus insurance £25, minus management £90, minus allowance for void (£900/12 = £75) = monthly cash flow of approximately -£145. This property is cash flow negative despite a 5.4% gross yield.
ROI on cash invested: deposit of £50,000 plus transaction costs of approximately £9,000 = £59,000 invested. If cash flow is -£145/month = -£1,740/year, the cash-on-cash return is negative. Capital appreciation of 3% per year on £200,000 = £6,000/year equity gain. Total return including appreciation: £6,000 - £1,740 = £4,260/year on £59,000 invested = 7.2% ROI. This is the complete picture — and it is meaningfully different from the headline yield.
How to Use the Calculator
The True Buy-to-Let ROI Calculator takes all cost inputs — mortgage rate and LTV, management fees, maintenance provision, void period, insurance, and tax rate — and produces a genuine monthly cash flow figure and annual ROI on capital invested. Running it on any property under consideration before purchase shows whether the investment is viable at current costs and rates, not just at headline yield.
Related calculator: Use our Rental Yield Calculator to compare gross and net yield with costs included.