Plan on 12 months minimum of sub breakeven performance. Plan on the first 5 months at zero revenue, then a slow incline.
If it is a brick/mortar (physical location) then have reserves to carry a minimum of 8 months.
Calculate your operating expenses (power/phone/lease/cost of goods etc...), put each as a line item on an excel spreadsheet.
Then do a worst case guess on revenue, start at $0 on month 1, then increase it by 5 to 8% per month (based on a realistic revenue stream).
Have your operating expenses compound on a month by month basis. Subtract the revenue from it (you will see no real money as you are either reinvesting, or recovering expenses). At the point where that monthly balances to zero, you are at break even operationally (not profitable, nor investment recouped).
Use that value to determine your reserves you need to begin (add a "precolumn" with capital invenstments, buildouts etc...).
Don't go in without a cash reserve buffer, especially with a retail.
I had a retail operation begin Nov of last year. It hit breakeven operationally in 6 months. It is now in month 10 and is profitable. That is an anomoly, don't plan on that rapid of a return. I had demographic marketting tragetted and agressively hit the market with a specific plan which worked out. If it had not, I would be sitting on another 18 months of poor performance from that location.
Just a coupla thoughts.