The more complicated the budgeting process is, the less likely a person is to keep up with it. The purpose of a personal budget is to identify where income and expenditure is present in the common household; it is not to identify each individual purchase ahead of time. How simplicity is defined with regards to the use of budgeting categories varies from family to family, but many small purchases can generally be lumped into one category (Car, Household items, etc.). The budgeting process is designed to be flexible; the consumer should have an expectation that a budget will change from month to month, and will require monthly review. Cost overruns in one category of a budget should in the next month be accounted for or prevented. For example, if a family spends $40 more than they planned on food in spite of their best efforts, next month's budget should reflect an approximate $40 increase and corresponding decrease in other parts of the budget. "Busting the budget" is a common pitfall in personal budgeting; frequently busting the budget can allow consumers to fall into pre-budgeting spending habits. Anticipating budget-busting events (and underspending in other categories), and modifying the budget accordingly, allows consumers a level of flexibility with their incomes and expenses. Special precautions need to be taken for families operating on an irregular income. Households with an irregular income should keep two common major pitfalls in mind when planning their finances: spending more than their average income, and running out of money even when income is on average. Clearly, a household's need to estimate their average (yearly) income is paramount; spending, which will be relatively constant, needs to be maintained below that amount. A budget being an approximate estimation, room for error should always be allowed so keeping expenses 5% or 10% below the estimated income is a prudent approach. When done correctly, households should end any given year with about 5% of their income left over. Of course, the better the estimates, the better the results will be. To avoid running out of money because expenses occur before the money actually arrives (known as a cash flow problem in business jargon) a "safety cushion" of excess cash (to cover those months when actual income is below estimations) should be established. There is no easy way to develop a safety cushion, so families frequently have to spend less than they earn until they have accumulated a cushion. This can be a challenging task particularly when starting during a low spot in the earning cycle, although this is how most budgets begin.