Planning for retirement can be complicated, and there are plenty of questions to ask yourself before you leave your job. How will you spend your free time? How will you pay for healthcare expenses? How much will you receive in Social Security benefits?

One surprising question many workers can't answer, though, is how much they already have saved for retirement. Nearly half of workers across all generations and 42% of baby boomers (the generation closest to retirement) say they don't know what they have in savings, according to a survey from Northwestern Mutual.

Knowing what you already have socked away in your retirement fund is the foundation of planning for your future. This question can be somewhat difficult to answer if you have several retirement accounts from multiple past employers, with your money spread across various 401(k)s and IRAs. However, when you're unsure of how much you have saved, it's tough to gauge whether you're on track for retirement.

Measuring your retirement progress

When you know how much you currently have stashed away for retirement, it's easier to tell whether you're behind, ahead, or right on track. But first, you have to know how much you'll need to have saved by the time you retire.

The easiest way to determine this number is to use a retirement calculator. Not all calculators are created equal, though, so be sure to check what factors are considered in the calculations. Some calculators will factor in Social Security benefits and inflation, for example, which can give you a more accurate snapshot of how much you really need to save.

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