The CalculateLot function is designed to automatically calculate the trading lot size based on risk management principles. It allows a trader to specify the percentage of the account balance he is willing to risk in a trade and determine the optimal position volume based on this.

Syntax

double CalculateLot(double riskPercent, double stopLossPips);

Parameters

Параметр        Тип     Описание
riskPercent     double  Процент от текущего баланса счета, которым трейдер готов рискнуть. Указывается в абсолютном значении (например, 2.0 = 2% от баланса).
stopLossPips    double  Расстояние до уровня Stop Loss в пунктах. Для 5-значных котировок указывается количество стандартных пунктов (например, 1000 = 1000 пунктов = 100 пипсов).

Return value

The function returns the normalised lot volume ( double ), which:

  • Conforms to the rounding rules to the volume step ( VOLUME_STEP );

  • Does not exceed the maximum allowed volume ( VOLUME_MAX );

  • Is not less than the minimum allowed volume ( VOLUME_MIN ).

If the calculated value exceeds the allowed limits, the function returns a limited value (minLot or maxLot).

Operating algorithm

  1. Obtaining account and symbol parameters

    • Current balance ( ACCOUNT_BALANCE )

    • Tick value ( SYMBOL_TRADE_TICK_VALUE )

    • Minimum, maximum and step of lot change

  2. Calculation of risk amount in deposit currency

    riskAmount = баланс × (риск% / 100)

  3. Calculation of lot volume

    lotSize = riskAmount / (stopLossPips × tickValue)

  4. Normalisation and validation

    • Rounding to the nearest step ( VOLUME_STEP )

    • Minimum and maximum value validation

Examples of use

Example 1. Basic use in an Expert Advisor

//+------------------------------------------------------------------+
//| |
//+------------------------------------------------------------------+
void OnTick()
{
   //--- Set risk 1.5% of balance and stop loss 500 pips
   double lot = CalculateLot(1.5, 500);
   
   //--- Check that the lot is calculated correctly
   if(lot > 0.0)
     {
      //--- Get current prices
      double ask = SymbolInfoDouble(_Symbol, SYMBOL_ASK);
      
      //--- Calculate levels
      double sl = ask - 500 * _Point;
      double tp = ask + 1500 * _Point;
      
      //--- Open a position
      trade.Buy(lot, _Symbol, ask, sl, tp);
     }
}

Example 2. Use in a script with error checking

//+------------------------------------------------------------------+
//| |
//+------------------------------------------------------------------+
void OnStart()
{
   double riskPercent  = 2.0;   // Risk 2% of the balance
   double stopLossPips = 1000;  // Stop loss 1000 points
   
   double lot = CalculateLot(riskPercent, stopLossPips);
   
   //--- Output information about the calculation
   Print("=== Lot calculation results ===");
   Print("Account Balance: ", AccountInfoDouble(ACCOUNT_BALANCE));
   Print("Risk, %: ", riskPercent);
   Print("The amount of risk: ", AccountInfoDouble(ACCOUNT_BALANCE) * riskPercent / 100.0);
   Print("Stop loss, points: ", stopLossPips);
   Print("Ticking cost: ", SymbolInfoDouble(_Symbol, SYMBOL_TRADE_TICK_VALUE));
   Print("Calculated lot: ", lot);
   Print("================================");
   
   if(lot <= 0.0)
     {
      Alert("Error: Lot calculation failed. Check the risk and stop loss parameters.");
     }
}