First of all you need to have a basking spot of at least 90 in the cage somehwere for proper digestions. ANother thing...how big is your snake now? Growth rates are different around different sizes. A burm will grow between 4-6 inches a month until around the 6 foot mark. then it might be around 4-5 a month . Finally slowing to around 3-4 a month by the time it is 8 1/2 feet. Then it slows ALOT around the 10-12 ft mark. It also depends on the sex ( male or female).
: these growth rates are on the recomended diet for a burm. Power feeding and underfeeding will change the results.