Please help me to understood the % of savings how Databricks are calculating DBCU

They are telling if I take DBCU 12500 plan the price will be with discount 12000 and 4% discount.

That means if I consume 12500 DBU, I am paying for this $12000 and 4% saving means without pre purchase it should be $12500, so that means 1$/DBU

but in JC I can get 0.3$/DBU.

Please help me to understand this on what basis DB calculating % of savings