With accounting, if everyone involved in the process of accounting followed their own system, or no system at all, there's be no way to truly tell whether a company was profitable or not. Most companies follow what are called generally accepted accounting principles, or GAAP, and there are huge tomes in libraries and bookstores devoted to just this one topic. Unless a company states otherwise, anyone reading a financial statement can make the assumption that company has used GAAP.

With GAAP, if GAAP is not the principles used for preparing financial statements, then a business needs to make clear which other form of accounting they're used and are bound to avoid using titles in its financial statements that could mislead the person examining it.

GAAP's in accounting are not cut and dried. However they're guidelines, and as such are often open to interpretation. They are estimates have to be made at times, and they require good faith efforts towards accuracy. You've surely heard the phrase "creative accounting" and this is when a company pushes the envelope a little (or a lot) to make their business look more profitable than it might actually be. This is also called massaging the numbers. This can get out of control and quickly turn into accounting fraud, which is also called cooking the books. The results of these practices can be devastating and ruin hundreds and thousands of lives, as in the cases of Enron, Rite Aid and others.

Personal accounting

It might seem obvious, but in managing a business, it's important to understand how the business makes a profit. A company needs a good business model and a good profit model. A business sells products or services and earns a certain amount of margin on each unit sold. The number of units sold is the sales volume during the reporting period. The business subtracts the amount of fixed expenses for the period, which gives them the operating profit before interest and income tax.

It's important not to confuse profit with cash flow. Profit equals sales revenue minus expenses. A business manager shouldn't assume that sales revenue equals cash inflow and that expenses equal cash outflows. In recording sales revenue, cash or another asset is increased. The asset accounts receivable is increased in recording revenue for sales made on credit. Many expenses are recorded by decreasing an asset other than cash. For example, cost of goods sold is recorded with a decrease to the inventory asset and depreciation expense is recorded with a decrease to the book value of fixed assets. Also, some expenses are recorded with an increase in the accounts payable liability or an increase in the accrued expenses payable liability.

Standard deduction - some personal expenditures or business expenses can be deducted from your income to reduce the taxable amount of income. These expenses include items such as interest paid on your home mortgage, charitable contributions and property taxes.