MACD in MetaTrader 5 — MQL5 Source Code

Here’s a fun quirk: MetaTrader’s built-in MACD draws the MACD line as a histogram and skips the classic MACD-vs-signal histogram entirely. So building your own isn’t just an exercise — it’s how you get the real, three-component MACD from the explainer on an MT5 chart.

What you’ll need

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

The source

We build the two EMAs onto internal buffers, subtract them for the MACD line, EMA-smooth that for the signal, and plot the difference as the histogram.

//+------------------------------------------------------------------+
//|                                                 AlgoGen.MACD.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_buffers 5
#property indicator_plots   3

#property indicator_label1  "Histogram"
#property indicator_type1   DRAW_HISTOGRAM
#property indicator_color1  clrMediumSeaGreen
#property indicator_width1  2
#property indicator_label2  "MACD"
#property indicator_type2   DRAW_LINE
#property indicator_color2  clrDodgerBlue
#property indicator_width2  2
#property indicator_label3  "Signal"
#property indicator_type3   DRAW_LINE
#property indicator_color3  clrOrangeRed
#property indicator_width3  2

input int InpFast   = 12; // Fast EMA period
input int InpSlow   = 26; // Slow EMA period
input int InpSignal = 9;  // Signal EMA period

double HistBuffer[], MacdBuffer[], SignalBuffer[];
double FastEMA[], SlowEMA[];

int OnInit()
  {
   SetIndexBuffer(0, HistBuffer,   INDICATOR_DATA);
   SetIndexBuffer(1, MacdBuffer,   INDICATOR_DATA);
   SetIndexBuffer(2, SignalBuffer, INDICATOR_DATA);
   SetIndexBuffer(3, FastEMA,      INDICATOR_CALCULATIONS);
   SetIndexBuffer(4, SlowEMA,      INDICATOR_CALCULATIONS);
   IndicatorSetString(INDICATOR_SHORTNAME,
      StringFormat("AlgoGen MACD(%d,%d,%d)", InpFast, InpSlow, InpSignal));
   return(INIT_SUCCEEDED);
  }

// Recursive EMA helper writing into buf[i].
void EmaStep(const double &price[], double &buf[], int i, int period)
  {
   double k = 2.0 / (period + 1.0);
   if(i == 0) buf[0] = price[0];
   else       buf[i] = price[i] * k + buf[i - 1] * (1.0 - k);
  }

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[])
  {
   int start = (prev_calculated > 0) ? prev_calculated - 1 : 0;

   for(int i = start; i < rates_total; i++)
     {
      EmaStep(close, FastEMA, i, InpFast);
      EmaStep(close, SlowEMA, i, InpSlow);
      MacdBuffer[i] = FastEMA[i] - SlowEMA[i];
      // Signal = EMA of the MACD line.
      double k = 2.0 / (InpSignal + 1.0);
      SignalBuffer[i] = (i == 0) ? MacdBuffer[0]
                        : MacdBuffer[i] * k + SignalBuffer[i - 1] * (1.0 - k);
      HistBuffer[i] = MacdBuffer[i] - SignalBuffer[i];
     }
   return(rates_total);
  }
//+------------------------------------------------------------------+

Install & compile

1. Drop AlgoGen.MACD.mq5 in MQL5/Indicators/ and press F7 to compile.
2. Drag it onto a chart — it opens in a separate window with the blue MACD line, orange signal line, and green/red histogram, matching the output chart.

Gotchas

• Calculation buffers. FastEMA and SlowEMA use INDICATOR_CALCULATIONS, so they hold intermediate values without being plotted — the clean way to carry the two EMAs bar to bar.
• Recompute the last bar. Starting at prev_calculated - 1 re-runs the most recent (still-forming) bar each tick while leaving history alone.
• MQL4? Same math. MQL4 has iMACD, but it (like MT5’s built-in) doesn’t give you the MACD-vs-signal histogram — the hand-rolled version above ports directly by swapping the OnCalculate signature and buffer setup.

Same indicator elsewhere: Python, Pine Script, EasyLanguage, NinjaScript. Then backtest a MACD 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.