Lot size based on risk / stoploss

//++++ These are adjusted for 5 digit brokers.
double  pips2points,    // slippage  3 pips    3=points    30=points
        pips2dbl;       // Stoploss 15 pips    0.0015      0.00150
int     Digits.pips;    // DoubleToStr(dbl/pips2dbl, Digits.pips)
int init(){
    if (Digits == 5 || Digits == 3){    // Adjust for five (5) digit brokers.
                pips2dbl    = Point*10; pips2points = 10;   Digits.pips = 1;
    } else {    pips2dbl    = Point;    pips2points =  1;   Digits.pips = 0; }
    // OrderSend(... Slippage.Pips * pips2points, Bid - StopLossPips * pips2dbl
...
//+------------------------------------------------------------------+
//| Lot size computation.                                            |
//+------------------------------------------------------------------+
double  LotSize(double SLpoints){
/*double    TSSF.value, TEF.value;          // Import from ComputeTSSF
//double    at.risk;                        // Export to init/start/OpenNew */
    /* This function computes the lot size for a trade.
     * Explicit inputs are SL relative to bid/ask (E.G. SL=30*points,)
     * Implicit inputs are the MM mode, the MM multiplier, count currently
     * filled orders by all EA's vs this EA/pair/period count and history.
     * Implicit inputs are all used to reduce available balance the maximum
     * dollar risk allowed. StopLoss determines the maximum dollar risk possible
     * per lot. Lots=maxRisk/maxRiskPerLot
     **************************************************************************/

    /*++++ Compute lot size based on account balance and MM mode*/{
    double  ab  = AccountBalance();
    switch(Money.Management.F0M1G2){
    case MMMODE_FIXED:
        at.risk = Money.Management.Multiplier;
        break;
    case MMMODE_MODERATE:
        // See https://www.mql5.com/en/articles/1526 Fallacies, Part 1: Money
        // Management is Secondary and Not Very Important.       // %used/trade=
        at.risk = MathSqrt(Money.Management.Multiplier * ab)/ab; // ~const rate.
        at.risk = MathSqrt(Money.Management.Multiplier * ab
                            * MathPow( 1 - at.risk, OrdersTotal() ));
        break;
    case MMMODE_GEOMETRICAL:
        at.risk = Money.Management.Multiplier * ab *
                MathPow(1 - Money.Management.Multiplier, OrdersTotal());
        break;
    }
    double  maxLossPerLot   = SLpoints * PointValuePerLot(),
    /* Number of lots wanted = at.risk / maxLossPerLot rounded/truncated to
    /* nearest lotStep size.
    /*
    /* However, the broker doesn't care about the at.risk/account balance. They
    /* care about margin. Margin used=lots used*marginPerLot and that must be
    /* less than free margin available. */
            marginFree      = AccountFreeMargin()*0.95, // Allow some slack
            marginPerLot    = MarketInfo( Symbol(), MODE_MARGINREQUIRED ),
    // So I use, the lesser of either.
            size = MathMin(marginFree / marginPerLot, at.risk / maxLossPerLot);
    /*---- Compute lot size based on account balance and MM mode*/}
    /*++++ Combine TSSF and trade size*/{
    double  minLot  = MarketInfo(Symbol(), MODE_MINLOT);
    if (size < minLot){ // Multiple orders -> no free margin
            // [risk=9.48USD/40.80, margin=10.62/1334.48, MMM=1x1, ExtraOO=0]
            //       0.23                  0.007
        Print(
            "LotSize(SL=", DoubleToStr(SLpoints/pips2dbl, Digits.pips), ")=",
            size, " [risk=", at.risk, AccountCurrency(),    "/", maxLossPerLot,
                    ", margin=",    marginFree,             "/", marginPerLot,
                    ", MMM=",       Money.Management.F0M1G2,"x",
                    Money.Management.Multiplier,
                    ", ExtraOO=",   OrdersTotal(),
                "]" );
        return(0.0);    // Risk limit.
    }
    if (!TSSF.Enable01) double  adjFactTSSF = 1;
    else                        adjFactTSSF = MathMin(1,TSSF.value);
    if (!TEF.Enable01)  double  adjFactTEF  = 1;
    else                        adjFactTEF  = MathMin(1,TEF.value);
    double  LotStep     = MarketInfo(Symbol(), MODE_LOTSTEP);
    size =  MathMax( minLot
                   , MathFloor(size*adjFactTSSF*adjFactTEF/ LotStep)*LotStep
                   );
    /*---- Combine TSSF and trade size*/}
    at.risk = size * maxLossPerLot; // Export for Comment
    return(size);
}   // LotSize
double PointValuePerLot() { // Value in the account currency of a Point of Symbol.
    /* In tester I had a sale: open=1.35883 close=1.35736 (0.00147)
     * gain$=97.32/6.62 lots/147 points=$0.10/point or $1.00/pip.
     * IBFX demo/mini       EURUSD TICKVALUE=0.1 MAXLOT=50 LOTSIZE=10,000
     * IBFX demo/standard   EURUSD TICKVALUE=1.0 MAXLOT=50 LOTSIZE=100,000
     *                                  $1.00/point or $10.00/pip.
     *
     * https://forum.mql4.com/33975 CB: MODE_TICKSIZE will usually return the
     * same value as MODE_POINT (or Point for the current symbol), however, an
     * example of where to use MODE_TICKSIZE would be as part of a ratio with
     * MODE_TICKVALUE when performing money management calculations which need
     * to take account of the pair and the account currency. The reason I use
     * this ratio is that although TV and TS may constantly be returned as
     * something like 7.00 and 0.00001 respectively, I've seen this
     * (intermittently) change to 14.00 and 0.00002 respectively (just example
     * tick values to illustrate). */
    return(  MarketInfo(Symbol(), MODE_TICKVALUE)
           / MarketInfo(Symbol(), MODE_TICKSIZE) ); // Not Point.
}

I posted my codes for doing this in this thread: https://www.mql5.com/en/forum/127798/page2#356736

It might help.

I tried yours, but had to adapt it to pass in the symbol (for other reasons). The numbers seem way off in the result though compared to the results I had with the above code. I can't decipher why, but the above code works 100% on regular brokers and yours seems to make too big of a trade.

Here is where I wonder if it all goes wrong:

int nDigits = 1;
int _Digits = MarketInfo(symbol, MODE_DIGITS);
if( _Digits == 3 || _Digits == 5 ) nDigits = 10;

int POINTS = CalculatePoints(symbol, price, stoploss);
double lotSize = CalculateLotSize(symbol, POINTS * nDigits, AccountEquity()*(RiskPercentage/100.0));

Should I even have the* nDigits? Does TICKVALUE need to be adjusted such as that or is that causing my lots to be too small?

As WHRoeder pointed in several of his posts - TICKVALUE should be always used in combination with TICKSIZE because sometimes TICKSIZE may not be equal to Point, e.g. your Point may be 0.00001 but TICKSIZE may be 0.00002. If that hapens than TICKVALUE will also be doubled so their ratio will also give you the correct result but you should always use them together.

PointValuePerLot()

/////////////////////////////////////////////////////////

double perc_lot_by_stop_f(double Stop_points)

{

double lose_on_stop_lose=Stop_points*(MarketInfo(Symbol(),MODE_TICKVALUE)/100);

double propotion=(AccountBalance()/100*Lot_perc_by_stop)/lose_on_stop_lose;

double Loto_=MarketInfo(Symbol(),MODE_MINLOT)*propotion;

if(Loto_>MarketInfo(Symbol(),MODE_MAXLOT)) Loto_=MarketInfo(Symbol(),MODE_MAXLOT);

return(Loto_);

}