Williams %R in MetaTrader 5 — MQL5 Source Code

Williams %R in MQL5 is a compact separate-window oscillator — a nice, short custom indicator. See the explainer for the concept and the negative scale.

What you’ll need

• MetaTrader 5 with MetaEditor
• Save as AlgoGen.WilliamsR.mq5 under MQL5/Indicators/

The source

//+------------------------------------------------------------------+
//|                                            AlgoGen.WilliamsR.mq5 |
//|                                          Copyright 2026, AlgoGen |
//|                                           https://www.algogen.io |
//+------------------------------------------------------------------+
#property copyright "Copyright 2026, AlgoGen"
#property link      "https://www.algogen.io"
#property version   "1.00"
#property indicator_separate_window
#property indicator_minimum -100
#property indicator_maximum 0
#property indicator_buffers 1
#property indicator_plots   1

#property indicator_label1  "%R"
#property indicator_type1   DRAW_LINE
#property indicator_color1  clrDodgerBlue
#property indicator_width1  2
#property indicator_level1  -20.0
#property indicator_level2  -80.0

input int InpPeriod = 14; // %R period

double WRBuffer[];

int OnInit()
  {
   SetIndexBuffer(0, WRBuffer, INDICATOR_DATA);
   IndicatorSetString(INDICATOR_SHORTNAME, "AlgoGen %R(" + (string)InpPeriod + ")");
   return(INIT_SUCCEEDED);
  }

int OnCalculate(const int rates_total, const int prev_calculated,
                const datetime &time[], const double &open[],
                const double &high[],   const double &low[],
                const double &close[],  const long &tick_volume[],
                const long &volume[],   const int &spread[])
  {
   if(rates_total < InpPeriod)
      return(0);

   int start = (prev_calculated > InpPeriod) ? prev_calculated - 1 : InpPeriod - 1;

   for(int i = start; i < rates_total; i++)
     {
      double hh = high[i], ll = low[i];
      for(int j = 1; j < InpPeriod; j++)
        {
         if(high[i - j] > hh) hh = high[i - j];
         if(low[i - j]  < ll) ll = low[i - j];
        }
      double range = hh - ll;
      WRBuffer[i] = (range == 0.0) ? -50.0 : -100.0 * (hh - close[i]) / range;
     }
   return(rates_total);
  }
//+------------------------------------------------------------------+

Install & compile

1. Drop it in MQL5/Indicators/, press F7.
2. Drag onto a chart — a separate window shows the %R line between −100 and 0 with the −20/−80 level lines, matching the output chart.

Gotchas

• Fixed scale. indicator_minimum -100 / indicator_maximum 0 pin the sub- window so the levels sit correctly; without them MT5 auto-scales and the −20/−80 guides drift.
• Flat-range guard. (range == 0.0) ? -50.0 fills a neutral mid-value when the window is perfectly flat instead of dividing by zero.
• Built-in / MQL4. MT5 has iWPR; MQL4 does too. The custom version is for learning and for exposing the buffer to an EA.
• Using it in an EA. Read the buffer with CopyBuffer, and consider gating signals on a trend filter (e.g. only buy %R crossing up through −80 when price is above a long moving average) — fading extremes blindly gets punished in trends.
• Add smoothing. For calmer signals, average the raw %R with a short SMA on a second buffer; %R is unsmoothed and pokes the extremes often.

Same indicator elsewhere: Python, Pine Script, EasyLanguage, NinjaScript. Then test a %R rule in AlgoGen.

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This post is educational, not financial advice. Indicators describe the past; they don’t predict the future. Backtest anything before you risk real money on it.