What determines success or failure?

The success or failure of your plan depends on the financial decisions that effect your income and expenses every year. The most important decisions are your savings rate, retirement age, life expectancy, and return on investments.

The other two large effects, taxes and inflation, are conditions you have to live with in the real world. You should be realistic and conservative in estimating values in your plan for these important forces. Don't try to make your plan work by decreasing the inflation or tax rate below what experts reasonably expect.

Is it real?

The answer you get in Results is accurate to the extent that your assumptions about the future match what really happens. For example, the answer is accurate only if you save what you predict you'll save and get the investment returns that you forecast.