Administered vs declarative regime
With domestic brokers the administered regime withholds tax on capital gains automatically. With foreign brokers (most serious MT5 brokers) you're in declarative mode: you file gains yourself.
Loss compensation
Trading losses can usually be offset against gains of the same nature for up to 4 years, depending on jurisdiction. A detailed journal is essential: no docs, no offset.
Offshore brokers and reporting
Every foreign trading account must be declared even without gains. It's not optional. Your accountant must understand trading — if they don't, change accountant.
