A flat advertised at £1,700 per month can look like a strong investment. But the rent alone does not tell you whether the figures work. To understand how to calculate rental yield, you need to compare the annual rent with the full amount you have invested, then look honestly at the costs that will continue after completion.
For landlords in South East London, yield is a useful first check when comparing property opportunities in areas with different purchase prices and rental demand. It is not, however, a replacement for proper cash-flow forecasting, mortgage advice or local letting evidence. A higher percentage is only attractive if the tenancy, condition, compliance requirements and long-term prospects stack up too.
How to calculate rental yield: the basic formula
Rental yield is expressed as a percentage. The most common starting point is gross rental yield:
Gross rental yield = annual rental income ÷ property purchase price × 100
First, turn the monthly rent into an annual figure. A property let at £1,500 per month produces £18,000 a year before any costs. If it was bought for £300,000, the calculation is:
£18,000 ÷ £300,000 × 100 = 6% gross yield
That means the property generates annual rent equal to 6% of its purchase price, before expenses. It is a quick way to compare similar properties, particularly at the early stage of a search.
Gross yield is often the figure used in sales particulars and investment conversations because it is simple and easy to understand. The limitation is equally simple: landlords do not get to keep all of the rent.
Use the right purchase figure
Using only the agreed purchase price can make a property look more profitable than it really is. For a more realistic calculation, use your total acquisition cost instead. This may include Stamp Duty Land Tax, legal fees, survey costs, mortgage arrangement fees where applicable, broker fees and any immediate refurbishment needed before the property can be let.
For example, suppose you buy a property for £300,000 and spend a further £15,000 on tax, legal work and essential improvements. Your total investment is £315,000. With annual rent of £18,000, the adjusted gross yield is:
£18,000 ÷ £315,000 × 100 = 5.71% gross yield
That difference matters. It does not necessarily make the purchase a poor one, but it gives you a clearer starting point for comparing it with another property that needs less work or carries lower buying costs.
A note for cash buyers and mortgage buyers
The yield formula is the same whether you buy with cash or finance. However, a mortgage changes your monthly cash position significantly. Rental yield measures the property’s income against its value or cost. It does not show your return on the cash deposit, nor does it include mortgage interest.
A landlord using finance should therefore run two calculations: yield on the property and monthly cash flow after mortgage payments. Both need to be comfortable, particularly if interest rates rise or the property is empty for a period.
Calculate net rental yield for the fuller picture
Net rental yield accounts for the annual costs of owning and letting the property. The formula is:
Net rental yield = annual rent minus annual running costs ÷ total investment × 100
The running costs will vary by property and by landlord arrangement. Typical expenses can include letting and management fees, landlord insurance, service charges and ground rent on leasehold flats, maintenance, safety checks, licensing costs where relevant, accountancy fees and an allowance for void periods.
Imagine the same property produces £18,000 annual rent. Its yearly non-mortgage costs are £4,200, including management, service charges, insurance, repairs and a void allowance. With total acquisition costs of £315,000, the calculation becomes:
£18,000 – £4,200 = £13,800 net annual income
£13,800 ÷ £315,000 × 100 = 4.38% net yield
A gross yield of 5.71% and a net yield of 4.38% are both useful figures, but they answer different questions. The first helps you compare headline rental performance. The second is closer to the income the property may generate before mortgage costs and tax.
Do not leave out the less obvious costs
Underestimating expenses is one of the quickest ways to produce an overly optimistic yield. A newly refurbished house with no service charge may have a very different cost profile from a leasehold flat with a substantial annual charge. Equally, an older property may offer a tempting purchase price but require more frequent maintenance.
Voids deserve particular attention. Even in an area with steady tenant demand, there can be time between tenancies, delays while works are completed or periods where a property is marketed below the expected rent. Allowing for a few weeks without rent each year is more cautious than assuming 12 paid months without interruption.
Maintenance should also be treated as a regular budget, not an occasional surprise. Boiler repairs, appliance replacements, redecoration between tenants and small responsive jobs all affect the real return. A fully managed service can reduce the day-to-day burden, but management fees still need to be included in the numbers.
Rental yield is not the same as return on investment
Yield focuses on rental income. Your overall return on investment can also include capital growth or loss, finance costs and tax. A property with a modest yield in a well-connected location may still suit an investor seeking long-term growth, while another property may provide a stronger income yield but have less potential for price growth.
This is why there is no single ‘good’ rental yield for every landlord. It depends on your objective. If you need regular income to cover a mortgage and build a buffer, cash flow and net yield may be your priority. If you are investing over a longer period, you may accept a lower yield in return for a property type or location with stronger owner-occupier demand.
Tax also changes the final position. Rental profit is generally taxable, and the treatment of mortgage interest differs depending on whether the property is owned personally or through a company. Tax rules and individual circumstances vary, so it is sensible to take advice from a qualified accountant before relying on a projected after-tax figure.
Check the rent is achievable, not just advertised
A yield calculation is only as reliable as the rent you put into it. The asking rent for one attractive listing is not enough evidence on its own. Look at comparable homes that have actually let, taking account of bedroom count, condition, outdoor space, parking, transport links and whether the property is furnished.
In SE18, SE28 and SE2, small differences can affect tenant demand and achievable rent. A well-presented property close to transport or with usable family space may let more readily than a similar-sized home that needs updating. On the other hand, paying too much for those features can reduce the yield, so the purchase and rental figures must be considered together.
A local letting appraisal should give you a realistic rental range, not simply the highest number that makes the investment work. Build your forecast around a sensible figure within that range and treat any extra rent as upside rather than a certainty.
A practical way to compare two properties
When comparing opportunities, put each one through the same process. Estimate the annual rent, calculate the gross yield using the purchase price, then calculate the net yield using total acquisition costs and a realistic annual expense budget. Finally, test the monthly cash flow against your mortgage payment and a contingency fund.
Property A may show a 6% gross yield but carry high service charges. Property B may show 5.4% gross yield, yet have lower ongoing costs, a more straightforward layout to maintain and stronger demand from long-term tenants. The second property could be the better investment even though its headline figure is lower.
The most useful yield calculation is not the one that produces the highest percentage. It is the one that helps you make a decision with your eyes open. Before making an offer, take the time to sense-check the rent, add every likely cost and leave room for the ordinary surprises that come with being a landlord. That is how a promising property becomes a workable investment plan.
