50% or 200% ?
I know a guy grow his account from 20K to 20million in 10 years.
what is the reasonable and sustainable return for small account?
This is a "trader" forum. Therefore, I'll assume you know that and that you're not talking about investing.
1) You should spend more time with the guy "you know" that grew his account from 20k to 20 million in 10 years. If you really don't know him...you shouldn't mention him as if you're using him as a gauge.
Seriously, so many folks walk around saying they "know" a extremely profitable trader while at the same time they're not smart enough to do whatever it takes to hang out with that trader (in person) so that they can learn whatever it is that he/she is doing to consistently make so much money.
2) You should stay away from trading because I don't think you realize that most traders lose their money.
3) If you're serious about trading, go find a successful trader (in person) and then watch him/her trade in person for a long period of time (if the trader allow such). Next, then ask that trader your question instead of getting replies from online from folks you "don't know".
Not a reasonable way to plan your rate of return for sure : )