The 1% rule, cap rate, gross yield: useful filters, terrible verdicts
Rules of thumb exist to reject deals fast. People keep using them to approve deals — and that’s where they hurt you.
Every investor collects a few shortcuts: the 1% rule, gross yield, cap rate, the gross rent multiplier. They’re genuinely useful — a way to bin the obvious no’s in ten seconds without opening a spreadsheet. The mistake is treating a filter as a verdict. A number that’s designed to be fast is, by definition, leaving things out.
What each shortcut actually tells you
The 1% rule (monthly rent ≥ 1% of price) is an American back-of-envelope test that quietly assumes American costs and rates — it barely survives contact with European taxes and financing. Gross yield (annual rent ÷ price) ignores every cost of owning, so it always flatters. Cap rate (net operating income ÷ price) is better because it nets off operating costs — but it still ignores financing, taxes on the income, and what you paid to get in and will pay to get out. The gross rent multiplier is just gross yield wearing a hat.
None of them are wrong. They’re just answering a smaller question than “is this a good deal?” — and the gap between those two questions is exactly where money is made and lost.
A worked example: the 1% rule vs the truth
Round numbers, illustrative only. A flat priced at €200,000 renting for €1,000 a month passes the 1% rule exactly — €1,000 is 1% of €200,000 — and shows a 6% gross yield. On both shortcuts, it looks like a clean buy.
Then you net it out. Operating costs — management, insurance, maintenance, local property tax, the odd empty month — commonly run 25–35% of rent, so the €12,000 of gross rent becomes roughly €8,000 of net operating income. Against the €200,000 price that’s a 4% cap rate, not 6%. And you haven’t yet paid the transfer tax and fees to buy (which quietly raised your real entry price), the income tax on the rent, or the cost of selling one day. By the time the deal has survived the full round trip, the honest return can sit a point or two below the cap rate and well under half the gross-yield headline.
Every shortcut in that chain was arithmetically correct. Each just answered a smaller question than the last, and the deal quietly shrank at every step. That’s the pattern: the rules of thumb don’t lie, they just stop early — and “stops early” looks identical to “looks great” right up until you own it.
The gap the shortcuts skip
A real verdict has to survive the round trip: purchase taxes and fees on the way in, the true operating cost while you hold, the tax on the rent, the financing, and the selling cost on the way out. It also has to survive being wrong about the rent by 15%. Rules of thumb skip all of that — which is fine when you’re rejecting, and dangerous when you’re buying.
So use them the way they were built to be used: as a bouncer, not a judge. A deal that fails the 1% rule is almost always a fast no. A deal that passes has merely earned the right to be underwritten properly. DealPilot AI keeps the speed and adds the rest — it starts from the same fast read, then runs the full underwriting on real local data and hands you a plain BUY / HOLD / AVOID with the numbers behind it. Use the 1% rule to skim. Use the app before you wire a deposit.
- The 1% rule imports US costs and rates into a European deal.
- Gross yield ignores every cost of ownership — it only ever flatters.
- Cap rate skips financing, income tax, and the buy/sell round-trip.
- None of them stress-test a rent that turns out 15% too high.
- All of them reject well and approve badly.
The shortcuts, defined
What is the 1% rule in real estate?
The 1% rule is a quick screen that says a rental property’s monthly rent should be at least 1% of its purchase price — a €200,000 flat should rent for about €2,000 a month to pass. It’s a fast way to reject weak deals, but it’s an American rule of thumb that assumes American costs, taxes and mortgage rates, so it travels badly to European markets and should never be used to approve a purchase on its own.
What is a good cap rate?
A cap rate is annual net operating income divided by the property price, so it measures the unleveraged return after operating costs but before financing and taxes. “Good” is entirely market-dependent — a strong figure in a prime, low-risk city can look weak in a cheaper, higher-risk one, because a higher cap rate is partly compensation for higher risk. Compare a cap rate to other properties in the same market, never to a universal target number.
What is the difference between gross yield and net yield?
Gross yield is annual rent divided by price and ignores every cost of owning, so it always looks flattering. Net yield subtracts the real costs of ownership — management, maintenance, insurance, local property tax, void periods — before dividing by price, so it reflects what you actually keep. Net yield is usually a third to a half lower than gross, and it’s the number that matters when you’re deciding whether to buy.
What is the gross rent multiplier?
The gross rent multiplier (GRM) is the property price divided by its annual gross rent — a €200,000 flat renting for €12,000 a year has a GRM of about 16.7. A lower GRM looks cheaper relative to rent. It’s the same information as gross yield expressed the other way up, and it carries the same flaw: it ignores all operating costs, taxes and the buy/sell round-trip, so it screens deals but never verdicts them.
Why are rules of thumb unreliable for approving a property deal?
Rules of thumb are built for speed, which means they deliberately leave things out — financing, income tax, purchase and selling costs, and the risk that your rent estimate is 15% too high. That’s fine for rejecting obvious no’s fast, but the same omissions make them dangerously optimistic when a deal passes. They reject well and approve badly, so treat a pass as permission to underwrite properly, not as a green light.
Do rules of thumb like the 1% rule work in Europe?
Only as a rough first filter. The 1% rule, cap-rate targets and yield benchmarks were largely calibrated on US costs, taxes and mortgage structures, and European transfer taxes, income taxes and financing differ enough to change the answer. Use them to skim listings quickly, but underwrite any survivor with local, country-specific costs before committing — a shortcut that assumes the wrong tax regime can flip a verdict.
Rules of thumb are for skimming. Before a deposit, paste the listing and get the full underwriting — BUY / HOLD / AVOID, on real numbers.
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