Speaking of staff, unless you start your business with clients, employees can be a tremendous expense and involve more administrative time.Adding employees right from the get go with out having some type of clientele is risky at best.
Even the best planners can't see everything that might crop up, and being flexible is the key with any good business plan.
The best thing about doing a business plan is that it makes you think about the important elements of your proposed business.
One of the biggest decisions in the Computer Repair Business is whether to go retail location, or office building, or warehouse scenario. And there are quite a few associated costs like utilities, signage, furniture, and equipment.
Part of the decision making process on these different scenarios is to also consider whether you want to offer onsite service or inside service (where the customer brings in their equipment).
There are necessary activities that take away from billable hours.
Now if you work 80 hours a week, you could bill over 40, but that's not the same thing.
Another common area that is missed is the cost of training and technical resources like manuals and etc.
Both can get expensive and necessary if you want to keep your skills up to date.
And if you are a owner/operator (one man band) you will need to do many administrative, marketing, and record keeping tasks that all take away from billable time.
In fact, some of the most effective owner/operators I know in the computer repair business are ecstatic with a 70% bill ratio.