about greeks on butterfly, i would like to ask how from looking at the greeks i can know if there is still money to make? lets say theta is positive so it means I’m making money from decay but yet if gemma is negative any change in the underlying can not be profitable is there a way to calculate that theta has more value and its worth it to keep the trade?
You're assuming that a fly traded from a position that's neutral delta at the inception of the trade. 1) You can trade flies directionally and 2), volatility may decrease (implied or stat) thereby increasing gamma yet gaining from theta and/or vega. Perhaps cover when your initial theta position drops by half (stop loss) or doubles (target). Butterflies are a structure, not an edge. I rarely (if ever) trade flies that are neutral (to open).
negative "gemma"? Depending on your strikes (all OTM or far OTM, balanced, ITM, etc) and your planned time horizon, you may wish to consider what the odds are of PnL projections for remaining for a range of time, and exit accordingly (instead of relying solely on theta)! If you have a balanced delta-neutral position, theta may be a good metric to base exit on, but since theta can change with different configurations, that may not be ideal for all cases. A good question.
Gamma only increases drastically in the last week or so of trading, getting higher as DTE get closer. As long as you get out of the position at least a week out from DTE you are rarely exposed to any danger from Gamma. (this is my understanding). Theta is the hardest one for me to get ahead of. That is how much a short option will grow as time passes. In other words, assuming you set up a premium collection strategy and your break-even boundaries never get breached, then the theta should be paying you every day. HOWEVER, there are other things that seem to affect the theta (Delta, and gamma). Theta is a greek only worth worrying about if your underlying does not move at all, and if it was that easy we could all just sell straddles every day. But underlyings do move, and the math to figure out how much that affects your theta is pretty hard. Implied volatility also affects theta a lot. You can own a stock on earnings day that doesn't trade up or down after earnings are announced, but you still lose a ton from the drop in IV rank for the options. Bottom line - options are very complicated, and the people who seem to do best trade small, take profits when they can, and are very careful about what underlyings they select. NOT losing money on trades is just as important as having winning trades.