Hi Adam, to find a default value for the percentage of calf value attributed to the bull, this formula (in blue) was applied to a selection of cow/calf cost of production benchmarking studies (e.g., Forero et al 2017, Holmgren and Fenz 2015, Manitoba Agriculture 2017). The range was 3-7%, with an average of 5.5%. As this formula is quite sensitive to changes (a 0.5% increase in percentage of calf value attributed to the bull increases bull breakeven price by around $600 per head), the suggestion is to leave this parameter steady at 5.5% unless more data is known to the producer.