MT4 vs MT5: Key Differences for Expert Advisors

MT4 and MT5 look similar on the surface, but they are built on different programming languages and different underlying trade models, and that matters a lot once automation is involved. MT4 uses MQL4, while MT5 uses MQL5, a more modern, object-oriented language with a richer built-in function library. Code written for one is not directly compatible with the other; an EA has to be ported, not just copied over.

The bigger practical difference is how each platform treats open positions. MT4 is order-based: every trade is its own ticket, and you can have multiple separate buy and sell orders open on the same symbol at once, which is what makes classic hedging strategies straightforward. MT5 defaults to a netting system on most retail accounts, where multiple trades on the same symbol combine into one net position, though many brokers now also offer an MT5 hedging account mode. An EA written assuming MT4-style multiple independent tickets can behave completely differently, or throw errors, if it's run unmodified on a netting MT5 account.

Porting an EA between platforms usually means rewriting order-management functions, updating how the code references historical price data, and testing carefully in a strategy tester before going live, since subtle differences in execution or rounding can change results. MT5 also supports more asset classes and has a built-in economic calendar and deeper market depth data, which some newer EAs use to their advantage.

For a trader choosing between platforms, the practical question is usually which one your broker supports well and which one the specific EA you want to run was actually built and tested on, since a mismatch here is one of the most common causes of an EA not working as advertised.