Options stop loss calculator

Hi Everyone,

I was wondering if some kind soul out there could help me out. I am trying to figure out if I bought a put what I would have as a stop loss.

I was looking at this earlier so I will use this one as my example:
So if I thought the DIA etf was going to go down right now and I wanted to buy a Nov put with a strike of $149 it would cost $4.75. The delta is -54.1 and the gamma is 4.0. The etf is currently @ 148.25 and my trade idea would be invalid if it rose to 150, a gain of 1.18%.

So how would I calculate a stop loss for this?

Do I just use the 1.18% so if the option declines 0.57 then I exit? Or do I use the gamma and delta. This where i get really confused. I keep reading about option pricing and the more I read the less I know

If I read everything right if the etf moves to 150 then the $1 increase will decrease the value of my option by 0.54. So if the etf moved from 148.25 to 150 the my stop loss should be
Option price - [amount of decrease * delta]
or
4.75 - [1.75 * .54]

So would a stop loss of $3.75 be right?

Please excuse my ignorance, I am just starting to learn about options. They have always baffeld me so I decided that I was going to learn them this year. Thanks you for all your help and patience. I really do appreciate anyone taking the time to help a total newb!

Thanks guys for all of your input. I have traded DIA as a stock but fell in love with the idea of having a set amount of risk per trade, hence the options. I never even thought to look at the volume of the options, I just assumed since I have never had a real problem with fills in the etf that the options would be the same.

I think that i will drop the idea of using options for this, and maybe try my idea out on apple or the spy like you said. I have a pretty decent directional strategy, 50% win rate with the winners averaging double the losers going back 2 years, and thought that options would be a great way to not tie up so much capital on each trade.

I was also looking at the mini options yesterday. Seems interesting although I now have to go back and look at the volume

On the ones I do go with I will take your advice and stick to the more liquid options and set the option to sell if the underlying stock hits a price point with a limit order. I will also set an alert so that I can make sure I get out