Hello Amy,
There is no specific formula to calculate the mortality rate especially in PD patient. There were some studies that look at the predictors and factors associated with mortality and eventually predict the mortality of the patients. Most of the studies were done in HD population. (Kidney Int. 2015 May; 87(5): 996–1008- Development and validation  of a predictive mortality risk score from a European HD cohort). Perhaps by adapting to the HD population with some minor tweaks at the PD risk factors, the predictive mortality score can be used but it need a proper validation. However , there was some article on the use of surprise questions in PD cohort to predict one-year mortality. (Perit Dial Int. 2013 Jan-Feb; 33(1): 60–66). Maybe, this might give a little help in managing our patients on PD.