Even though the trading conditions are almost same in Demo and real/live MT4 trading accounts, there are one significant difference between them.
The difference is the Market Liquidity. There is no market liquidity in MT4 Demo accounts.
What is Market Liquidity?
There is always this market liquidity in every financial market.
This is also called a money liquidity, and this decides everything including price movements and order executions in financial markets.
For example, when you place a buy order of EUR/USD 10 lots, there needs to be someone selling EUR/USD 10 lots in total in the same market, otherwise your order cannot be executed.
When there is no counter order to match your order in the market, the trading servers may take necessarily actions such as slippage, re-quotes and order rejections.
Larger the volume is, harder the executions. More the liquidity is, easier the executions.
So what Demo trading accounts are missing? Yes, the market liquidity, no Demo MT4 accounts are connected to the real exchange market and these do not reflect the real market liquidity situation to the tradings.
So when you are trading in a MT4 Demo account, you are trading with nobody but just virtual demonstrations.
In the MT4 Demo accounts, some impossible orders in real/live accounts are also executed instantly.
The second difference in MT4 Demo accounts is about how you think of the profit/loss, so the psychological situation.
Using fake money and real money you have earned by hard-time working have really got different meanings to you.
In a MT4 Demo account, you might do some tradings without thinking deeply, but you might think a lot when you trade in a real/live trading account.
You can never compare the profit/loss in Demo and real/live trading account as the same.
MT4 Demo is only for practice
Traders Trust also offers MT4 Demo accounts for free.
These accounts are just for you to practice how to use MT4 Trading Platform and get a gist in Forex & CFD market.
EA strategy tester is also the same, the real profit/loss result and the result from the EA tester would be different, because the strategy tester does not reflect widened spread and market liquidity in the result.
So MT4 Demo accounts and EA strategy tester can be used to see the approximate result, but the specific numbers maybe not trustworthy.