This morning we got what we feared was coming: a numbers question. That's because there's about as many schools of thought regarding what figures should appear in a business plan as there are wantrepreneurs with Web 2.0 start-ups. Fortunately, our reader ignored all that and asked a question we can answer in under 10,000 words:

How do I project numbers for a business that exists only in my head?

We say: Make a good guess. Seriously. There's no way you can pin down hard and fast numbers for a start-up if it's not operational unless you're buying into a franchise. We're not saying that you should pull numbers out of thin air—but you can come up with educated figures that are supported by research. Here's a few ways to go about that:

As far as operating costs and expenses go, a few phone calls to area real estate agents or even business owners can give you a sense of what sort of numbers you're looking at for rent, utilities, etc. Figuring out the cost of goods (if that applies to your start-up) can be a little trickier, but a little digging on the Internet and calls to wholesalers or distributors can help you roughly nail down those numbers as well. If you can, try to find figures for businesses that are similar to yours or that operate in your industry. While that can be tough because those numbers aren't always available unless a company is public, it's worth an Internet search to see what you can turn up. Any hard data—whether it's census numbers for your region or conversion rates and click-throughs for an Internet business similar to yours—are useful. What you're looking for are figures that can help you substantiate and support the numbers you come up with in your business plan.

Lastly, see if you can find someone who works in the industry who can help you scale. Someone who's worked for 20 years in the field you're trying to penetrate can tell you whether or not your sales projections are a pipe dream, and whether your costs are reasonable. They can also help point out something you may have overlooked.

The bottom line is that the numbers don't have to be exact—but they should be well thought out and supported with data. While they will undoubtedly change, they should be in the ballpark of what you could reasonably expect in regards to costs and sales. Do your homework- because missing any major expenses or having over-inflated sales figures are an immediate tip-off to a lender or investor that you don't know what you're doing.