You can keep as far as you have enough margin.
The margin depends on your leverage and the currency you are dealing with.
So for example the required margin for 100,000 lot USD/JPY or USD/CHF on 1:100 leverage is $1000
if it is for the same trading lot and leverage in EUR/USD, it will also depend on the rate of exchange, so if the EUR/USD is 1.2140 then
the margin required is $1240
This is based on Fxsol margin calculation, you need to consult your broker or look up the calculation on your software.