margin can change all the time since it is calculated in realtion to volatility
so you need to check on a daily basis to make sure what it is
there is a set amount of margin required to trade - but some brokers will cut that amount
and during the normal trading hours when stock exchanges are open margin is normally charged at 50% of the normal rate
then once you are in a trade already - the margin amount to continue in the trade is then another amount lower
if you think about it - this is important since you might enter the trade with a margin of say 1,250 for the ym, and just have 1,250 in your account ( not possible as this is probably below the minimum amount you need for your account to operate - but the figure is just for the example) - the second the ym goes against you - you would be making a loss and therefore the value of you account would be below the 1,250 and you would get the trade closed -
to stop that happening - you are allowed to have a margin of say, 1,000 once you are in the trade - so there is a margin amount to open the trade and then a lower margin requirement once the trade is open, so as long as you stay above 1,000 - the trade will stay open - but if you close that trade and have less than 1,500 in your account - you would not be able to open a new trade
watch out for variances in timing of when the 50% margin applies - and check the time it finishes - quite often a period before the close - but also some brokers offer very low margin amounts which offer incredible leverage - dangerous if you are losing - great if you are winning