The branch reinforcement is based on compensating for displaced area of pipe wall. The calculation process is fairly straighforward. For a single branch you can do it manually. For a set of calculations I wrote up a simple spreadsheet.
Look at Appendix "H" of B31.3. It is a "primer" for understanding the area replacement method.
Ben Nottingham's Piping Office Suite is a set of ExCel spread sheets that will help with many of the B31 calculations. Branch connection calcs are included. There ain't no such thing as a free lunch. More often (if you are lucky) you will receive justthe value you pay for.
