Making a budget for a home business start-up is more of an art than it is a science. No matter how exactly you think you've pinned down all your expenses, it's guaranteed that more will appear that you either didn't think of or just couldn't have predicted. That's why you need to make sure that you always plan for every possible expense.
Remember that any equipment you buy can go wrong, no matter how expensive or high-quality it was (this is especially true of anything IT-related!) When things break, you probably won't need to buy a new one, but you'll at least have to wait for the manufacturer to replace what broke. This can lead to days of lost or less-efficient business, and cost you money. Budget for equipment failures.
People are Unpredictable.
When you hire staff, you have no way of knowing that they aren't going to let you down. You might have worked out that it takes $200 to train one new staff member, but what do you do when that newly-trained staff member quits and moves to France after three weeks at the job? You've got no choice but to train someone else and take the loss. Budget for staff turnover.
The World is Against You.
Or at least it can sometimes feel that way. Just when you've got everything perfect, someone sets up a little construction site next door, and drives your business away. Or maybe it rains for a few weeks, meaning that there's just no demand for your bouncy castle hire business. Whatever, you need to budget for times when you've got no customers -- and make sure you have something else to be getting on with in the meantime.
Customers are Out to Get You.
'The customer is always right', right? Well, yes, but their 'rightness' can sure cost you a lot of money. You have to be prepared to take huge losses to pay off complaining customers. Remember that one unhappy customer can undo hundreds of dollars worth of marketing efforts -- once you make a customer unhappy, your options are to take a loss fixing the situation or to take an even bigger loss when they tell everyone how you didn't. The only way to avoid this expense is to please all of the people all of the time, which just isn't possible. Budget for unhappy customers.
Competitors Kick You When You're Down.
If one of your competitors spots a good opportunity to take some business from you, they won't hesitate. You need to have a 'war chest' ready to make aggressive offers and marketing efforts, and be prepared to get into a full-scale price and advertising war with the competition. It's massively frustrating to be in a position where your rivals are getting all your business simply because you already used up your marketing money for this month. Budget for war.
Double Your Budget.
Whatever happens, remember that under-budgeting is the worst mistake you can make. It's known as 'under-capitalisation', and is generally thought of as one of the quickest ways to kill a business -- anyone who might be willing to give you finance will just think you're a fool if you've under-capitalised your business, and might even refuse to lend to you.
Most home businesses budget only a few thousand dollars for their expenses (if they even make a budget), thinking that they already have everything they need. People don't realise how quickly little costs like having some business cards made or getting your suit dry-cleaned start to add up. This doesn't apply for other kinds of business, but if you're like 99% of home business starters, you really ought to double your budget. If you doubt me, start adding up all your 'little' expenses over a year, and see what happens.
Budgeting for every expense in your initial plans shows that you're not the kind of person who thinks that everything's going to go right for them just because they're so great -- instead, you're a practical businessperson who knows that anything that could go wrong probably will, and you plan to make a profit anyway. There is a difference, after all, between arrogance and cool-headed determination, and it's one that the people with the money want to see.