lot size calculation error

[Luandre Ezra]

Hi all, I have a code to calculate a lot size. This code should calculate how much lot size I will buy or sell depending on the max risk percentage that I put.

this is the code to calculate lot size.

double OptimalLotSize(double maxRiskPrc, int maxLossInPips){
  double accEquity = AccountEquity();
  Print("accEquity: " + accEquity);
  
  double lotSize = MarketInfo(NULL,MODE_LOTSIZE);
  Print("lotSize: " + lotSize);
  
  double tickValue = MarketInfo(NULL,MODE_TICKVALUE);
  
  if(Digits <= 3)
  {
   tickValue = tickValue /100;
  }
  
  Print("tickValue: " + tickValue);
  
  double maxLossDollar = accEquity * maxRiskPrc;
  Print("maxLossDollar: " + maxLossDollar);
  
  double maxLossInQuoteCurr = maxLossDollar / tickValue;
  Print("maxLossInQuoteCurr: " + maxLossInQuoteCurr);
  
  double optimalLotSize = NormalizeDouble(maxLossInQuoteCurr /(maxLossInPips * GetPipValue())/lotSize,2);
  
  return optimalLotSize; 
}


double OptimalLotSize(double maxRiskPrc, double entryPrice, double stopLoss){
   int maxLossInPips = MathAbs(entryPrice - stopLoss)/GetPipValue();
   return OptimalLotSize(maxRiskPrc,maxLossInPips);
}

this is the code of sendorder.

if(   
            buySignalEMA               &&             //INDICATOR 1
            MACD < 0                   &&             //INDICATOR 2
            //rsiValue < rsiLowerLevel   &&             //INDICATOR 3
            Open[0] > currentFastEMA                  //condition not to buy again after price hit the stop loss
               ){              
            
         Print("Condition met, sending buy order");
         Print("Entry price = " + Ask);
         
         double stopLossPrice = NormalizeDouble(currentSlowEMA,Digits);         
         Print("Stop loss price = " + stopLossPrice);   
           
         double takeProfitPrice = Ask + 400*Point;   
         Print("Take profit price = " + takeProfitPrice);
                 
         double lotSize = OptimalLotSize(riskPerTrade,Ask,stopLossPrice);
         Alert("Lot size buy: " + lotSize);
         
         double minimumLotSize = MarketInfo(Symbol(),MODE_LOTSTEP);
         if(lotSize < minimumLotSize){
            Alert("lot size minimum unmet");
         }
                  
         orderID = OrderSend(NULL,OP_BUYLIMIT,lotSize,Ask,10,stopLossPrice,takeProfitPrice,NULL,magicNumber);
         
         if (orderID < 0){
            Print("Order send error, error code: " + GetLastError());

The error is when I open position the lot size that I would buy is around 16 to 18 lot size which is weird cause I set the maxRiskPrc only 2% of my account balance. I manually calculate the lot size code also and it seems find so I don't really know where the error is. I hope you guys can help me with this kind of error.

Thanks.

[William Roeder]

Risk depends on your initial stop loss, lot size, and the value of the symbol. It does not depend on margin and leverage. No SL means you have infinite risk. Never risk more than a small percentage of your trading funds, certainly less than 2% per trade, 6% total.

1. You place the stop where it needs to be — where the reason for the trade is no longer valid. E.g. trading a support bounce the stop goes below the support.
2. AccountBalance * percent/100 = RISK = OrderLots * (|OrderOpenPrice - OrderStopLoss| * DeltaPerLot + CommissionPerLot) (Note OOP-OSL includes the spread, and DeltaPerLot is usually around $10/pip but it takes account of the exchange rates of the pair vs. your account currency.)
3. Do NOT use TickValue by itself - DeltaPerLot and verify that MODE_TICKVALUE is returning a value in your deposit currency, as promised by the documentation, or whether it is returning a value in the instrument's base currency.
             MODE_TICKVALUE is not reliable on non-fx instruments with many brokers - MQL4 programming forum 2017.10.10
             Is there an universal solution for Tick value? - Currency Pairs - General - MQL5 programming forum 2018.02.11
             Lot value calculation off by a factor of 100 - MQL5 programming forum 2019.07.19
4. You must normalize lots properly and check against min and max.
5. You must also check FreeMargin to avoid stop out

Most pairs are worth about $10 per PIP. A $5 risk with a (very small) 5 PIP SL is $5/$10/5 or 0.1 Lots maximum.