double M_CalcMaxLotMargin(ENUM_ORDER_TYPE orderType)
{
   double price = (orderType == ORDER_TYPE_BUY)
                  ? SymbolInfoDouble(_Symbol, SYMBOL_ASK)
                  : SymbolInfoDouble(_Symbol, SYMBOL_BID);

   double marginPerLot;

   if(!OrderCalcMargin(orderType, _Symbol, 1.0, price, marginPerLot))
      return 0.0;

   double freeMargin = AccountInfoDouble(ACCOUNT_MARGIN_FREE);

   double maxLots = freeMargin / marginPerLot;

   // Auf gültige Lot-Schritte runden
   double lotStep = SymbolInfoDouble(_Symbol, SYMBOL_VOLUME_STEP);
   maxLots = MathFloor(maxLots / lotStep) * lotStep;

   return maxLots;
}