This is actually an excellent question. Lets take an example of 5 trades per month returning 10% each.
Some services would report it as sum of all trades (50% return). This assumes that you had just one trade open at any given time and allocated 100% of your portfolio to each trade. But some services would report it this way even if they had more than one trade open which would make it simply impossible to allocate 100% to each trade.
The next method is to report an average of all trades. This assumes you allocated 20% per trade, with no cash balance. Some services specifically recommend to keep at least 20% of the portfolio in cash, but report performance based on full allocation. This is simply not realistic and not reproducible.
I report model portfolio performance based on my recommended allocation of 10%. So in the above example, I would report 5% since I allocated 10% per trade and had 10% return per trade. For my portfolio, I have maximum 6 position at any given time, so 40% of the portfolio is in cash, but I still report return on the whole portfolio, not on the maximum invested capital. This reporting is called cash adjusted because it takes the cash reserves into consideration.
Reporting returns this way grossly underestimates the return compared to other services, but I want to be as realistic and transparent as possible. My model portfolio performance reports what was possible with fairly conservative allocation.