Congratulations on trying to actually plan your business before you open your doors. So many small start-up businesses fail to take this step. Sounds like you need an example of a business plan. You can find some samples to review and learn more about planning at market plan pro's website and at the Small Business Administration's website. SBA has small business development offices usually at local colleges and universities.
They have loads of free information, guides, and seminars that will save you time and money. There may be a SCORE chapter in your community where you can connect with a retired executive who will help you review your plan, for free.
In answer to your question, you must figure out the sales projections for each month, particularly if you have a seasonal business, to get to the 12 month total. Research your market carefully and a visit to the SBA development website will be the best place to go from here.
This is the best advice: after your research and calculations, if your plan says you will not break even in a reasonable amount of time, find another business to start unless you have unlimited funds. Cheers to your success!