This works just fine and all the values I get are exactly what I'm looking for, BUT the problem I'm having is for the column totals, using 'Show Partial Sums' in pivot. The totals all match the Q1 Actual i.e. it's not totalling the values in the column!
If I change the code to below
If([Medical/Surgical] = 'Medical', //If it's medical
([Q1 Actual]+([Q1 Actual]*(medicalGrowthFactor/100))) //Apply medical growth factor