Comprehensive lot size calculation function for mql4

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 You place the stop where it needs to be - where the reason for the trade is no longer valid.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. Account Balance * percent = RISK = (OrderOpenPrice - OrderStopLoss)*DIR * OrderLots * DeltaPerlot (Note OOP-OSL includes the SPREAD)
3. Do NOT use TickValue by itself - DeltaPerlot
4. You must also check FreeMargin to avoid stop out
   

My answer is: no and no.

Why did you vary your lot calculation (replicated below for illustration) based on whether the account currency was part of the currency pair? 

    ...
    if(crossCurr == AccountCurrency()) {
        lots = (riskCapital / stopLoss) / tickValue;
        Print("Calculated lots (A/C currency = Quote currency): ", lots);
    } else if(baseCurr == AccountCurrency()) {
        // 
        lots = ((Ask * riskCapital) / stopLoss) / tickValue;
        Print("Calculated lots (A/C currency = Base currency): ", lots);
    } else if(crossCurr != AccountCurrency()
           && baseCurr  != AccountCurrency()) {
        lots = riskCapital / (stopLoss * tickValue);
        Print("Calculated lots (A/C currency neither Base nor Quote currency): ", lots);
    }
    ...

If RiskAmount, StoplossValue, and PointValue (i.e., a ratio of tickvalue and ticksize) are all denominated in deposit currency, why the need to determine if the account currency is part of the currency pair?  I don't believe you need to do this.

I'm not sure what you mean by "adjusted", but stoploss in this calculation (i.e., lotsize = RiskAmount / StoplossValue) should be a value in deposit currency, not a size in pips or points.  

lots            = MathRound(lots/lotStep) * lotStep;

In the above code snippet, what will happen when you round up?  The answer is that you will risk more than you defined in your riskCapital.  I believe the better course is to always round down (using MathFloor()).

if(lots < minLot) {
    lots = minLot;
}

What about maxlot?  While most of us will probably never reach our brokers' defined maxlot (mine is 50 standard lots and I'm still only trading at <=1 standard lot), it is better to check the calculated lotsize against maxlot just to make sure. 

The following is the fixed fractional position size function that I'm currently using.  It isn't perfect, but it might give you some insight to my comments above.

double PositionSize_FixedFractional(int StoplossDistance_inPoints, double RiskPercent, double AcctBalance = 0) {
   double lotstep = MarketInfo(Symbol(), MODE_LOTSTEP), 
          minlot = MarketInfo(Symbol(), MODE_MINLOT), 
          maxlot = MarketInfo(Symbol(), MODE_MAXLOT);
        
   // validate passed parameters
   if (RiskPercent <= 0 || StoplossDistance_inPoints <= 0)
      return (minlot);
   else if (AcctBalance <= 0)
      AcctBalance = AccountBalance();
      
   // calculate raw lotsize
   double PointValue = MarketInfo(Symbol(), MODE_TICKVALUE) / (MarketInfo(Symbol(), MODE_TICKSIZE) / Point),
          RiskAmount = MathFloor(AcctBalance * RiskPercent / 0.01) * 0.01,
          StoplossValue = StoplossDistance_inPoints * PointValue,
          lotsize = RiskAmount / StoplossValue;
                   
   // condition raw lotsize
   lotsize = MathFloor(lotsize / lotstep) * lotstep;
   lotsize = MathMax(MathMin(lotsize, maxlot), minlot);
   
   // return conditioned lotsize
   return (lotsize);
}

. 

 double PointValue = MarketInfo(Symbol(), MODE_TICKVALUE) / (MarketInfo(Symbol(), MODE_TICKSIZE) / Point),

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. Account Balance * percent = RISK = (OrderOpenPrice - OrderStopLoss)*DIR * OrderLots * DeltaPerlot (Note OOP-OSL includes the SPREAD)
3. Do NOT use TickValue by itself - DeltaPerlot
4. You must also check FreeMargin to avoid stop out
   

WHRoeder,

Re what you put:

1. don't understand what you mean, please clarify

2. I've already calculated risk, so I don't understand your point here either.

3. You presumably have predicted that in my code, tickValue is calculated as

double tickValue            = (MarketInfo(Symbol(),MODE_TICKVALUE));

and from your other forum post of DeltaPerLot, it should be

double tickValue            = MarketInfo(Symbol(),MODE_TICKVALUE) / MarketInfo(Symbol(),MODE_TICKSIZE;

?

4. I am already checking AccountFreeMargin in the line which assigns a value to riskCapital - or did you mean elsewhere?

Thanks

Thirteen, thanks for your input.

I varied my calculation due to http://www.babypips.com/school/undergraduate/senior-year/position-sizing/calculating-position-sizes.html which suggests different calculations based on different scenarios. I've been hacking around with mql4 for a few months now, but it sounds from your post that there is a way to get round these differences.  Surely having different ways of calculating lot size mentioned on the above URL, I need to represent this in code? 

Good point about rounding down - I should be doing that.  Also good point about maxlot, which I need to change.  I also see in your code about the SL calc as an amount rather than a number of pips.  Cheers

What do you think about WHRoeder's modification of your code in his most recent post?  That's quite a significant difference.

double PointValue = MarketInfo(Symbol(), MODE_TICKVALUE) / (MarketInfo(Symbol(), MODE_TICKSIZE) / Point),

1. This has nothing to do with the code I posted above.
2. Yes, I understand your equation.  We are saying the same thing, just expressing it in a different way.  Your DeltaPerlot is similar to my PointValue.
3. As you can see, I'm not using TickValue alone.  Not sure why you repeated this mantra.
4. I do a FreeMargin check in another part of the code.  

double PointValue = MarketInfo(Symbol(), MODE_TICKVALUE) / (MarketInfo(Symbol(), MODE_TICKSIZE) / Point),

If you ask something like that, you still got a lot of homework to do.

Have you ever try different calculation logic and figure out why it happen like that?

Please post an example which shows: (1) risk amount, (2) stoploss distance, (3) currency pair, (4) tickvalue, (5) ticksize, (6) Point, and (7) the value of MarketInfo(Symbol(), LOTSIZE).

Couple of quick things to remember: the stoploss distance you give to the function must be in integer points, and the RiskPercent must be decimal form (e.g., 10% = 0.1 and 2% = 0.02).