Rent vs buy: the math that actually decides it

Most rent versus buy arguments compare a rent payment with a mortgage payment and declare the mortgage the winner, because at least part of it builds equity. That comparison is broken before it starts. It puts two different kinds of money side by side and pretends they are the same thing.

A mortgage payment is two things wearing one coat

One part of the payment repays the loan. That money does not disappear: it moves from your bank account into the house, from one pocket you own into another, and you are neither richer nor poorer for the transfer. The other part is interest, and interest goes to the bank and never comes back. Rent is entirely the second kind. Every payment leaves. So of course rent looks worse next to a mortgage payment, because you are comparing pure cost against cost plus saving. Line up only the money that disappears on each side and the question finally becomes answerable.

The renter's side is short

It is the rent. Contents insurance, and the cost of moving when a lease ends, but essentially the rent. Nothing comes back, and nothing is hidden either, which is worth noticing: a renter can state their annual unrecoverable cost to the euro without opening a spreadsheet. The buyer's version of that number is much harder to pin down, and the parts that are hard to pin down are exactly the parts that get left out. What a renter is exposed to is not really the money, it is the contract: the rent can be raised at a review, and a landlord can decide to sell or to move back in. How much protection you have against either is written into local tenancy law, not into your budget, and that is the thing worth reading before you sign.

The buyer's side is longer than the brochure suggests

Mortgage interest. Property tax or its local equivalent, Grundsteuer in Germany, taxe foncière in France, IMU where an Italian property is not the main home. Buildings insurance. Any service charge on an apartment. Then the transaction itself, at both ends: the notary, the land registry, the transfer duty, the estate agent on the way out. None of that is recoverable, and it is spent in exactly the way rent is spent. In France the entry costs even have a household name, the frais de notaire, which is a slight misnomer because most of that money is tax rather than the notary's fee. Every market has its own version, and it is always bigger than a first-time buyer expects.

Maintenance is a bill, not a maybe

A roof is fine for decades and then costs a great deal in a single week. A boiler dies in February. Windows, wiring, a bathroom that was modern when you moved in. As a tenant you pay for all of this too, quietly, inside the rent, but the landlord carries the timing. As an owner you carry it yourself, and it never arrives on a convenient date. The workable answer is to treat maintenance as a yearly amount you set aside whether or not anything broke, sized off what the building would cost to rebuild rather than off what you paid for it. Older housing stock costs more to keep standing than new stock, and pretending otherwise does not make the roof last longer.

Your deposit is not sitting still, it is working somewhere

Here is the half that gets dropped. A deposit is capital, and capital always has an alternative job. Put it into a property and it works there, in one building, on one street, in one city, in one currency. Leave it invested and it works there instead. Whichever you choose, you gave up the other, and that forgone return is a genuine cost of buying which never appears on any mortgage statement.

It is also a concentration decision. A deposit that took a decade to assemble is usually the largest single thing a household owns, and converting it into one undiversified asset is an asset allocation choice whether anyone calls it that or not. Your total net worth may barely move on completion day. Its shape changes completely.

How long you stay is the variable that decides it

The transaction costs are paid in two lumps, one when you buy and one when you sell, and they are then spread across however many years you owned the place. Stay two years and they sit heavily on each of those two. Stay fifteen and they thin out to something small. Same flat, same rent, same loan, and the answer flips on nothing but time.

So the real question is never whether to buy. It is how many years this particular purchase needs before it beats renting the same place, and that number is your break-even horizon. If your honest estimate of how long you will live there is shorter than it, renting is the cheaper option, whatever your family thinks. Comparing one lump of costs today against a stream of rent stretching over many years is precisely the job present value was invented for: a payment you make now weighs more than the same payment in year twelve, and discounting is how you get both onto one scale instead of naively adding up columns.

A sanity check you can do in an afternoon

Take the asking price and divide it by one year of rent for a comparable place nearby. The answer tells you how many years of rent that purchase costs. German buyers do this constantly and call it the Kaufpreisfaktor. Say one flat comes out at twenty and another at thirty-five: the second is expensive relative to what it produces, in the same sense that a share can be expensive relative to its earnings. The ratio settles nothing on its own, because the sensible level depends on borrowing costs, on how fast rents move in that market, and on the fees and taxes the local system attaches to owning. What it does is stop you comparing a specific flat against a rule of thumb somebody wrote about a different country.

The forced-saving argument, taken seriously

The best real argument for buying is behavioural rather than financial. A mortgage is a payment you cannot quietly skip, and the repayment portion builds a pot that many households would never have built on purpose. That is true, and it is not a small thing. Plenty of people reach the end of a loan owning something they could not have accumulated by intending to invest the difference each month.

But look at what the argument concedes. It says buying wins because the alternative does not get done, not because the alternative is worse. If you genuinely would invest the gap every month, including in the year the market falls and the news is ugly, that edge collapses. Judge yourself on evidence rather than intention. What happened to your last pay rise?

What it does to your balance sheet

The house appears as an asset and the mortgage as a liability, so the bottom line often looks similar the week after you buy. What changed is liquidity. Almost nothing you now own can be reached without selling the place you sleep in, and selling takes months, costs a slice of the price, and cannot be rushed without accepting a worse one. Worse, the timing tends to correlate: the same downturn that costs somebody a job can be the one cooling the local property market, so the moment you most need to sell is often the moment selling is hardest. If you have never separated liquid from total net worth, buying is the moment that distinction starts to bite.

When the numbers should lose

Wanting to knock a wall down. A school you want your children to stay in. An ageing parent two streets away. Never again having an inspection scheduled by someone else. Those are real reasons and the arithmetic does not outrank them. Local conditions are real too: Germany has an unusually large long-term rental market and strong tenant protection, so renting for life there is ordinary rather than a failure to launch, while in Italy high home ownership makes buying feel less like a decision and more like a stage of adulthood. Neither culture is wrong. But each one quietly sets a default, and a default is not an analysis.

So do the small version before the next viewing. Write down two annual totals: the rent on the place you would otherwise live in, and the buyer's unrecoverable costs, meaning interest, property tax, insurance, maintenance and the purchase and sale fees divided across the years you honestly expect to stay. Whichever total is lower is ahead that year, and now you can see by how much and decide what the difference buys you. If you want to weigh two streams of money properly instead of just totalling them, run them through present value first.

Written by

Federico Romaldi

Co-Founder, Worthmap

Published: August 14, 2026

Federico is a co-founder of Worthmap, a wealth-intelligence platform built for serious investors. With a background in software engineering and a long-standing passion for value investing, he created Worthmap to bridge the gap between net-worth tracking and investment analysis.