Annual Increases in Earned Income. During your working years, typically your earned income will increase. Annual salary increases tend to follow the economy. In recent years average salary increases have been in the 3% to 4% range. For example, according to an article from Salary.com, in 2003, the average salary increase rate was 3.4%. If you aren't sure, 3% is a reasonable assumption.

Services/Benefits: If you provide services to your family -- that is, perform chores that benefit your family like child care or even mowing the lawn -- these services have a value that your family would have to pay someone else to do. Similarly, if your employer provides benefits to you that benefit your family, the cost of replacing those benefits should also be taken into consideration. This will vary depending on your own circumstances and other factors, such as your occupation. If you aren't sure, $10,000 a year is probably a reasonable estimate.

Tax Bracket/Rate: For 2007, if your federal income tax filing status is Married, filing jointly, and your annual taxable income is between $63,700 and $128,500, your federal Marginal Tax Rate is 25%. If your annual taxable income is between $128,500 and $195,850 it would be 28%. Federal tax rates are, of course, subject to legislative change. Depending on where you live, you may also be subject to state income taxes. If you aren't sure, 28% may be a reasonable rate to use.

Monthly Expenses. The amount that you spend on yourself each month depends on your own circumstances and lifestyle. This amount would include the cost of your clothes, food, transportation, hobbies, entertainment, etc. If you aren't sure, you could use an amount equal to about 15% of your monthly earned income. For example, if you earn $84,000 a year, that means $7,000 each month and 15% of $7,000 is $1,050.

Investment Return Rate: The actual rate of return that you believe your family would earn would be dependant on the type of investments they selected. It is important to remember that future rates of return can't be predicted with certainty and that investments that offer higher rates of return are subject to higher risk and volatility, and may result in a loss of principal. Over time, the actual rate of return on investments can vary widely, especially for long-term investments. From January 1970 to December 2005, the average compounded rate of return for the S&P 500, including reinvestment of dividends, was approximately 11.4% per year. During this period, the highest 12-month return was 61%, and the lowest was -39% (reflecting a loss). Of course, past performance is no guarantee of future results and you cannot invest directly in an index. In recent years, savings and money market accounts offered by banks have paid as little as 1% interest or even less. If you aren't sure, a 5% rate of return is probably reasonable.