The question is in the title. Is there any rule for this? For example warrants are exercised when avg price > strike price.
You should check if the convertible preferred stock is dilutive by comparing it to the basic EPS. This is done by dividing the preferred dividend (forgone if the convertible debt are converted) by the number of shares created if it was converted. For example a 100 par value 10% preferred shares are convertible into 50 shares of common stock. We will do the following: (100x0.1)/50= 0.2
If the figure given above (in this case 0.2) is less than the basic EPS then it is dilutive and should be included in the calculation of dilutive eps.