This Annuity Calculator is a simple spreadsheet by Vertex42.com that is useful for retirement planning. It simulates a situation where a person makes regular withdrawals from an account that is earning interest. The calculations are based on general finance theory, so it might not apply to the various types of "insurance" annuities. However, it can be used to calculate the payout for some types of Immediate Annuities. It also allows you to enter an annual inflation rate to simulate the case where you want to increase the amount that you withdraw each year (to keep up with rising expenses for example). The spreadsheet contains a second worksheet tab (not shown in the screenshot) that can help run some simple calculations to solve for different values. For example, you might want to solve for the Principal (or nest egg) required to allow you to withdraw $2000 per month for 20 years. The formulas are explained in detail on the official author page (see the Help link in the spreadsheet).