Abstract: A computer-implemented method for surgical planning and/or surgical navigation. A surgical navigation and/or planning system is also provided, that can include aspects of the computer-implemented method, which allows virtual implant planning, and receives real-time data from a tracker. The system can also include one or more hardware components which allow real-time imaging of one or more surgical instruments onto, relative to or over a patient's anatomy. The system and computer-implemented method improve the precision and safety of image based surgery, for example precision placement of bone implants during surgery. A software application is used to manage drill-guide assisted surgery and image-guided surgery. This provides a method and system for Computer Assisted Surgery (CAS) which improves accuracy and safety of a variety of surgical procedures.