A variable cost is a cost that changes as at different points overtime and is not a set amount every month. Raw materials and rent are monthly payments made each month that typically do not fluxuate at all unless there is a new agreement, expansion or something that causes a change with those bills. Equiptment machinery repair can change because there are not repairs made each month. The cost and extensiveness of the repairs fluxuates over time therefor this is a variable cost.