Whether you’re in the dark about your retirement savings or want to double-check your strategy, there are dozens of free online calculators. Here’s how to find the one that’s right for you…

Two types. The first type is best for people who don’t want to spend much time entering data and don’t mind letting the tool make some assumptions on their behalf. The second type asks you more questions and makes fewer assumptions. It may require some digging to get the data to plug in. These are better for people nearing retirement.

Check with your plan first. Your retirement plan administrator may have a calculator for its clients that will work with the data it already has about you.

Simple calculators. Try the Vanguard Retirement Nest Egg Calculator (Vanguard.com/nesteggcalculator), New Retirement’s Simple Retirement Calculator (NewRetirement.com) or AARP’s Retirement Calculator (AARP.org/work/retirement-planning/retirement_calculator.html).

Complex calculators. For something a bit more sophisticated, try the T. Rowe Price Retirement Income Calculator (TRowePrice.com) and Fidelity Retirement Income Planner (Fidelity.com), or one called The Flexible Retirement Planner (FlexibleRetirementPlanner.com/wp).

Caution: Pay attention to the assumptions the calculator is making on your behalf. Is it operating under an overly rosy view of stock market performance? Is it assuming that you’ll need much more or less than you actually plan to live on during retirement? Also, avoid the temptation to “puff up” your input by plugging in numbers from a particularly good year—that may feel reassuring but will skew your results.

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