You can double your coins in a month with altcoin I guess, if you choose the right coin and buy it at the right time, but again it involves risk and luck if both favors you then you can make it huge.
you can actually double your investment in a much shorter period of time. maybe even in two weeks time with trading altcoins and there is always an altcoin which is being pumped these days.
for example although i am not an expert and i am not taking big risks i have been making a nice profit with XMR by trading it for the last week.
Exactly, the price of XMR went from 0.007 to 0.16 in 5 days time so if you would have invested when price was 0.007 then you would have doubled your coins only in 5 days.
if people can predict it with 100% right im sure he will get huge profit,currently im mining ethereum clasic, lastday people says ethereum is more profitable but im still mining etc, today the price of etc riding and i get more benefit with holding it.
other case im buying etc at price 370 waiting price rise to back 600 but fail to 200 last day..
so for me no people can predict anything with 100% right.
Yeah its difficult to predict anything when it comes to altcoin or bitcoin as anything is possible with it, make sure that you buy and sell at right time to grab some profits.