Depending on the type of contract established with your company.
Unused budget is either:
Carried over to the next month and therefore you will be able to spend your normal amount plus the remaining amount of the previous month.
If your company has chosen the "top-up" option, the unused budget is topped up at the end of the month and you have the same budget amount at the beginning of each month.
If you are not sure which option applies to you, ask your benefit manager or if you have, check your intranet page.