Retirement calculators can help us plan and prepare to retire. When we are years away, these online tools can help us determine how much we should be saving. As we approach our time to retire, they can help us understand how much we can spend each year and which accounts should fund that spending.

Not all retirement tools, however, reach the same result. They take different approaches to what is a complex series of calculations and assumptions. One study examined five popular retirement planning software packages and found stark differences in outcomes. As a result, it recommended that individuals use “multiple programs before implementing an action plan based on the results.”

To that end, here is a list of the best retirement calculators, planners and software tools.