I don't think there can be a straightforward answer to this question. It depends on the trader's trading style. account size & the trading strategy.
I'll assume for the sake of this example that your strategy has an edge, meaning it can make positive pips over time after paying the brokerage costs. Then it is a question of scaling & your account size.
a. Consider the max. number of losing trades in a row to come up with the risk percentage per trade.
b. Your account size to calculate the actual risk per trade.
For example, if your strategy can definitely make you let us say 200 pips on EUR/USD in an year, then if you are trading 10 Standard Lots throughout the year, which is a totally consistent lot size, then you can expect to make R375,000 in a year at the current USDZAR rates.
But if you are trading 1 Mini lot, then you can expect to make R3750 in a year, with the exact same example.
How does it relate to account size? In order to trade 1 mini lot, ideally, you would want to have R3750 in your account balance. Why? If on an average you are losing 10 pips on a trade, and you lose 1 trades in a row, you will still be able to place the exact same lot size. Because the distribution of the winners & losers can appear in any way, to make you net net 200 pips in an year in this example.
So, it really depends. There is no exact answer to this question. I would say, instead of focusing on the gains, focus on the process.
Focus on how you can develop a strategy & risk controls, that will definitely allow you to make 200 pips (any value here) from EUR/USD (or any instrument for that matter) in a year. And then execute it flawlessly. Then it is a matter of scaling it.
