Q:

Is it possible to know the probability that a trade is successful?

I'm trying to model the distribution of different outcomes of day trading every day for a year. I'm starting with $350 dollars. I'm only doing options trading on Apple stock with a 5% stop loss and a 15% stop gain. And if it doesn't hit one of those stops, I sell before the market closes.
I'm not trying to find a way to control whether I win or lose on the given day, I'm just gonna do my best. But at least in the long run is there a way to use the law of large numbers so that after a year, my average is close to the probability of winning on a given day?
If I flip a coin every day for a year, I can get all heads, yeah, but it's  way more likely that I get within 3 or 4 from half heads.
Is there a way to set up my option trade for the day so that it has a specific probability? Or at least on certain days that have certain conditions, will there be a pretty specific probability?
I've tried to learn "the secret to making money on the stock market", but I think for an average joe like me, I'm better off just trying to treat it as much like a coin flip as possible.
And by having certain limits on my orders, I get the impression that a probability can be calculated.

A:

If you had a trading system, and by trading system I mean the criteria setup that you will take a trade on, then once a setup comes up at what price will you open the trade and at what price you will close the trade.
As an example, if you want to buy once price breaks through resistance at $10.00 you might place your buy order at $10.05.
So once you have a written trading system you could do backtesting on this system to get a percentage of win trades to loosing trades, your average win size to average lose size, then from this you could work out your expectancy for each trade that you follow your trading system on.

