How to convert an MT4 Expert Advisor to MT5

Updated 5 November 2026

MetaTrader 4 and MetaTrader 5 look alike, but their languages differ where it matters for an Expert Advisor: orders, indicators and price data. This guide explains what changes, converts an EA with QuantForge’s free converter, and shows how to check the result.

What changes between MQL4 and MQL5

	MQL4	MQL5
Trades	Orders, selected with OrderSelect	Positions, orders and deals, sent with MqlTradeRequest
Indicators	iMA(...) returns a value	iMA(...) returns a handle; values come from CopyBuffer
Prices	Bid, Ask, Close[1]	SymbolInfoDouble, iClose or CopyRates
Inputs	extern	input (read-only)
Entry points	init, start, deinit	OnInit, OnTick, OnDeinit
Accounts	Always hedging	Hedging or netting

Rewriting all of that by hand is where conversions usually break.

Convert the source

1. Open the MQL4 to MQL5 converter and paste your .mq4 code, or drop the file in the app’s converter.
2. The converter keeps your code and adds MQL5 versions of the MQL4 functions it calls (OrderSend, OrderSelect, iMA, MarketInfo and the rest). It only rewrites what can’t work that way: price arrays, extern inputs and the old entry points.
3. Read the notes. Each one has a line number: a custom indicator to convert too, a DLL that must be 64-bit, arithmetic with Period(), error codes that MQL5 numbers differently.
4. Download the .mq5 (free account), or build the .ex5 directly on Pro.

Compile and compare

1. Put the .mq5 in MQL5 → Experts, open it in MetaEditor and press Compile. Fix anything the notes pointed out.
2. In the MetaTrader 5 Strategy Tester, choose a hedging account, the same symbol and dates you used in MetaTrader 4, and the same inputs.
3. Compare the number of trades, the entry times of the first few trades and the net profit. Small differences are normal (different tick generation and history); different entry logic is not, and the first differing trade shows you where to look.
4. Run it on a demo account for a while before going live.

Or rebuild it once for both platforms

If you’ll maintain the EA for a long time, rebuild its rules from blocks in the no-code EA builder: one project exports both .mq4 and .mq5, and you can backtest it in the browser.