Margin interest

What your broker charges for lending you the money to buy more than your cash covers. It is billed monthly against a debit balance, it compounds quietly while the position is open, and it is a real cost of the year — but in Spain it is not deductible: only administration and custody fees can be set against investment income, and interest is expressly excluded from a share's acquisition cost. Track it so you know what your leverage cost you, not to subtract it.