From SCORE Richmond by Doug Carleton: 

If you decide to sell your business what is a potential buyer going to look at first when your business goes up for sale?  Most probably it is going to be “How much money can I make from this business?”  Otherwise why buy it unless they are looking for an expensive hobby. How much cash flow your business generates that will be available to the new owner will also be a major driver of the value of your business, so you must make sure that you don’t leave anything out to your detriment, and be able to document it.

Determining owner’s cash flow is not that difficult if you know your P&L’s inside out.  There are the obvious things like profits – the sales minus the expenses.  But it is in those expenses that many of the important items reside that can be added back to the cash available to a new owner.  There may be interest expenses that you are paying now that the new owner will not have.  Add them back.  Your salary is in there.  Add it back.  There could be depreciation and amortization which, while they are an expense to the business do not require you to write a check.  Add it back.

A little less obvious are possible perks that you have given yourself as owner.  Things such as a company car; insurance premiums that the company may pay on your behalf; if you have done any business travel are there any personal expenses in there?  Add them back.  Finally if there were any non-recurring expenses during the year – something that happened that was not part of the business day-to-day operations that had to be paid for.  Add it back.  And finally, if your business includes real estate on which you have a mortgage, the interest expense will not be there for the new owner so add it back.  This total cash that the business throws off is going to be one of the most important numbers used in some business valuation formulas.  But it will also be the critical number for a lender if the new buyer is looking for a loan.  It tells the banker how much cash is available to service the debt which is the most critical thing that a lender wants to see first.

So make sure you get everything.  What you might miss might be money left on the table in the final offer that a buyer might make.