How HazNúmeros Calculates Rental Profitability

Most rental yield tools show you a number without showing their work. Since that number can shape a real investment decision, we think it's worth explaining exactly what goes into ours — what counts as income, what counts as a cost, and where the boundaries of the calculation are.

The pipeline

Every calculator on this site runs on the same underlying engine, so the methodology described here is consistent across the site, not reinvented per calculator:

your inputs → income calculation → expense calculation → yield/profitability → result

Income

Gross annual rent is simply monthly rent × 12. From that, we subtract vacancy loss (monthly rent × vacant months) to get a more honest income figure — see our guide to vacancy assumptions for why this matters more than most people expect.

Expenses

We separate two different questions that are easy to conflate: what counts as a real operating cost (for an honest profitability picture) versus what's tax-deductible (a narrower, legally-defined list for IRPF purposes — see our guide to what counts as a rental expense). The yield calculator currently models real operating costs — community fees, IBI, insurance, maintenance — as a single annual figure you provide.

The denominator: total acquisition cost, not just price

This is the methodology choice most likely to make our numbers differ slightly from a quick mental calculation or another tool: we divide by purchase price + buying costs + initial renovation, not price alone. Buying costs (ITP/IVA, notary, registry, gestoría) are real cash you put into the deal — excluding them flatters the yield. See our full breakdown of this choice for the worked example and the reasoning.

What the result means — and doesn't mean

• Gross yield = annual rent ÷ total acquisition cost.
• Net yield = (annual rent − vacancy loss − annual expenses) ÷ total acquisition cost.
• This net yield is before income tax. It does not include IRPF or, for non-resident owners, Modelo 210 withholding. We're building a dedicated tax calculator to cover that layer — until then, treat the result as pre-tax operating return, not a final take-home number.
• It does not include mortgage financing. The calculation treats the property as bought outright; if you're financing the purchase, mortgage interest and principal sit on top of this result as a separate cash-flow layer.

What's deliberately conservative, not optimistic

A few defaults are set to avoid flattering the result: 1 month of vacancy per year as the starting assumption (not zero), a confidence flag that marks a result "needs review" if vacancy is set to zero or expenses look implausibly low relative to rent. The goal is a number you can actually trust enough to act on, not the most impressive-looking number the inputs could produce.

Quick answers

Why doesn't the calculator ask for my marginal tax rate? The current calculator is deliberately scoped to pre-tax yield — see above. Tax treatment is different enough (and consequential enough) that it deserves its own dedicated tool rather than being bolted on as an afterthought.

Can I trust the default values? Treat every default as a reasonable starting assumption, not a prediction for your specific property. Replace each one with your own researched numbers before making a real decision — the calculator's value is in showing you how sensitive the result is to each input, not in guessing correctly for you.

See the methodology in action

Try the rental yield calculator yourself with your own numbers.

This article offers general, educational information and does not constitute tax, legal, or financial advice.