Guide

How to analyse the profitability of a buy-to-let property

Gross yield is only the first filter. This guide explains the metrics that actually decide a property investment —net yield, cap rate, leveraged cash flow and scenarios— and how to read them with judgement.

Starting point

Gross yield is only the first filter

Gross yield —annual rent divided by purchase price— is the most quoted metric when comparing rental properties. It is also the most misleading: it ignores the costs of owning the property, the effect of financing and the risk that the estimated rent won't hold.

A property with an apparently attractive gross yield can turn into a negative-cash-flow deal once operating costs and the mortgage instalment are deducted. Deciding on gross yield alone is deciding on incomplete information.

The metrics

The metrics that actually decide

These are the metrics that separate a surface reading from serious analysis. None is enough on its own; together they give the full picture.

Metric	What it measures	Reading
Gross yield	Annual rent / purchase price	Quick first filter, not conclusive
Net yield	Rent − operating costs, over price	Real return before financing
Cap rate	NOI / price	Compares assets on a like-for-like basis
NOI	Rent − operating costs	The asset's cash-generating capacity
Leveraged cash flow	NOI − debt service	Real monthly liquidity for the investor
Leveraged ROE	Net profit / equity invested	Return on the money you put in
DSCR	NOI / debt service	Cushion against the instalment (≥1 = self-funding)

Hidden costs

From gross yield to net return: what gets deducted

The jump from gross to net yield usually costs 1.5 to 2.5 percentage points in residential. These are the costs that explain it:

Property tax

Annual property tax (IBI) and municipal charges.

Community fees

Ordinary fees and, above all, unexpected one-off levies.

Insurance & upkeep

Home and rent-default insurance, plus a repairs reserve.

Vacancy & turnover

One vacant month per year equals ~8% of annual rent.

Management

Delegating to an agency typically costs 8–12% of rent.

Arrears

A prudent buffer for non-payment and recovery periods.

Leverage

How the mortgage changes the picture

Financing the purchase amplifies both return and risk. Leveraged ROE can comfortably exceed the cap rate when the cost of debt is below the asset's return —and turn negative when it isn't.

The key figure is leveraged cash flow: rent minus all costs minus the instalment. If it's negative, you're putting money in every month to keep the investment afloat. DSCR (NOI over debt service) measures that cushion: below 1, the deal doesn't fund itself.

Sensitivity

One scenario isn't enough

The most common mistake is building the analysis on a single optimistic scenario. A 50-basis-point rate rise, an extra vacant month or a special levy can flip the verdict entirely.

Rigorous analysis tests at least three scenarios —base, conservative and stress— and watches how cash flow behaves in each. The relevant question isn't 'how much do I make if everything goes well?', but 'can I hold on if it goes badly?'.

Legal framework

Rent caps in strained-market areas

In areas declared strained residential markets, the rent you can set is capped by the reference index (SERPAVI). An estimated rent above the applicable cap not only inflates returns on paper: it may not be legally enforceable.

Before projecting a rent, it's worth checking it against the current index for the area and property type.

From theory to decision

How to apply it to a specific property

To move from theory to a well-founded decision:

01
Start from real data: price, market rent and area costs.
02
Compute net yield and cap rate, not just the gross figure.
03
Model the leveraged scenario with realistic financing terms.
04
Put the deal through a stress test (rates, vacancy, levies).
05
Check the projected rent against the applicable SERPAVI index.

Frequently asked questions

What counts as a 'good' residential rental return?

It depends on the area, the risk and your cost of capital. More important than a universal number is whether the deal survives an adverse scenario. There is no single threshold that fits every case.

Gross yield or cap rate?

Gross yield works as a quick first filter; cap rate, which deducts operating costs, lets you compare assets on a like-for-like basis. To decide, you need both, plus leveraged cash flow.

How does the mortgage affect returns?

It amplifies both return and risk. It can raise ROE when the cost of debt is below the asset's return, and sink cash flow if rates rise or the rent doesn't hold.

Is this investment advice?

No. This is informational content. Ratio Planning provides quantitative analysis and does not constitute investment advice within the meaning of Directive 2014/65/EU (MiFID II) nor a personalised recommendation.

Ratio Planning provides quantitative analysis. The reports and tools do not constitute investment advice within the meaning of Directive 2014/65/EU (MiFID II) nor a personalised recommendation.

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