The advertised rent is maybe two-thirds of the story, so budget in three layers. First, the move-in lump sum: deposit, commonly one to two months; first month's rent; agent commission where tenants pay it, often around a month; plus smaller one-offs like contract or registration fees and utility connection charges. Realistically, that means having roughly three to four months' worth of rent in hand before you get keys, and more in markets known for heavier upfront customs, so check your specific country's norms.
Second, the true monthly cost: rent plus building or community fees where they're billed separately, utilities that scale with climate and apartment quality, internet, and any parking or storage.
Third, the irregular layer people forget: renter's insurance where customary or required, occasional maintenance and replacement costs that fall on tenants, furniture if unfurnished, and an exit buffer, since moving out has its own costs like end-of-tenancy cleaning, and your deposit comes back after you've already paid the next place's deposit.