Monthly; each month. Indicates something occurring or measured on a month-by-month basis.
電気代は月ごとに請求される。
Electricity bills are charged monthly.
売り上げは月ごとに集計して報告する予定だ。
Sales will be totaled and reported month by month.
支出を月ごとに管理すれば貯金がしやすくなる。
If you manage expenses monthly, it's easier to save money.