What is the failure rate for this contraceptive method?

What are the chances of me getting pregnant on the 28th day of a 30 day cycle?I am 100% sure I ovulated around the 15th day of my cycle.During ovulation my mood and discharge become noticeablly different.We also plan on pulling out.Using a condom is NOT an option so please don't bother telling me to use one.My partner would just like to know how risky it is by getting a percentage.I know that if executed perfectly the pull out method is 94% effective and peeing before sex clears any sperm left over from previous ejaculations from getting into the pre-ejaculatory fluid.However my partner still wants a percentage of the chances of us getting pregnant?And sources would be great.Thank you