While you are working, you pay Social Security Taxes (a form of retirement saving), and you are saving additional amounts (hopefully!) to secure your financial future. 

The remainder of your income provides for your lifestyle and living expenses, including income taxes. 

In retirement, your sources of income include Social Security, an employer pension (if you are lucky enough to have one), assets provided by employer contributions to a 401(k) or 403(b) plan, and your own assets and future savings.

Although not shown on the chart, you may also have part-time work  to supplement your retirement income. This could (and should!) be factored into the analysis.

The two variables that are most within your control are how much you save when you are working, and when you expect to retire.

Saving has two beneficial effects: First, it means that you're adjusting your lifestyle and living expenses to a lower level of income. Second, it provides more money to spend during your retired lifetime.

Likewise a later retirement date has two beneficial effects: First, it gives you more time to accumulate money for retirement. Second, it reduces the length of time over which you have to spread your retirement assets, making more money available each year. 

Being on track to meet your future financial goals starts with finding the balance between current and future lifestyle choices that's right for you. A good initial starting point is to aim for a level of post-retirement income that's consistent with your pre-retirement lifestyle and living expenses.