1. Breakup value
Breakup value is calculated by taking the current market value of all assets of the business, then deducting the liabilities and reasonable liquidation fees. The resulting value is what you would end up with if you sold off the assets and paid off all the liabilities. That is the value of the business on a "breakup" basis.
2. Going concern value
Going concern value is arrived at through a rather complicated process. This involves "normalizing" earnings, eliminating the impact of assets or revenue streams that do not form part of the core asset base or main revenue stream of the business. These assets and ancillary revenue streams are valued separately. Appropriate capitalization rates reflect reasonable levels of risk given the nature of the business.
The basic question
The basic question to be answered in valuing a business is, "How much am I willing to pay someone for a business if in paying that amount, I will receive a stream of future income from that business of $X annually?"
In determining this value, review the historical earnings stream, adjusting for the financial impact of unusual events such as a one-time windfall profit or an unusually large non-recurring expense. Common adjustments may also be required to reflect such things as "normal" wages of the management, reflecting what the business would have to pay in wages if it had hired a manager at market rates.
Once you have determined what the "normalized" future earnings would likely be, based on historical data and trends, select an appropriate capitalization rate. Consider the level of risk associated with the business and the rates of return on other types of investments. To put this range into perspective, look up the current payout rate for Guaranteed Investment Contracts (GICs), which are risk-free and can be cashed in at any time. Compare that to venture capitalists who require annual compound rates of return in the 25% to 30% range, since they typically invest in high-risk, high-return businesses by way of unsecured equity investments. Somewhere between these 2 ranges is where most businesses fall.
Before making a commitment on this purchase, you should seek the advice of a professional business valuator.