How long you stay. Stamp duty, registration and brokerage run about 8 percent up front, and selling costs more. Stay three years and the friction alone eats the gain. Buy when you will hold it long enough to earn the paperwork back.

The gap between yield and rate. You can rent a metro flat for about 3.5 percent of its price a year. Borrowing to buy it costs about 8.5. That five point gap is the running cost of owning, before maintenance and tax. When it is wide, renting and investing the difference is a real option.

What the down payment earns instead. Money in walls is money not in the market. If the flat compounds faster than your portfolio, buying wins. If not, the locked capital is the cost. Owning still buys things a sheet cannot price, control, forced saving, a hedge against rising rent. Just count them honestly.