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.

Older woman sitting in front of computer looking at documents.

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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.

An important factor when calculating your retirement number is the current amount you have in savings. So be sure to comb through all your various retirement accounts and add up how much is saved in each to get an accurate idea of how much you have total. If you simply guess how much you have, it could throw off your entire retirement plan. For instance, if you think you have more than you actually do, you may save less each month than you should while thinking you're on track. Then once you reach retirement age, you'll have less than you anticipated, and it will be too late to catch up.

Once you have a retirement number in mind and know how much you need to save each month to get there, take a look at the amount you're setting aside right now. Are you currently saving less than you should? If you're behind, can you increase your savings enough to catch up? When you know where you stand, you'll have a better idea of how you need to adjust your retirement plan to reach your goals.

Saving more when you're falling behind

The truth is most people are behind on their savings -- even those who are nearing retirement age. The median amount baby boomers have saved in their retirement accounts is just $152,000, according to a report from the Transamerica Center for Retirement Studies. Also, the average American age 65 and up spends around $46,000 per year, the U.S. Bureau of Labor Statistics found. At that rate, the average retiree will burn through $152,000 worth of savings in just over three years.

If you know your savings are falling short, though, that's the first step to making the necessary corrections to get back on track. Once you've determined how much you need to save by retirement age and what you should be saving each month to get there, take a look at your budget to figure out where you can save money. Map out all your expenses as accurately as possible, then divide them up into categories to help separate the truly necessary expenditures from the nice-to-have ones.

First, weed out the unnecessary expenses you can easily live without. For instance, if you're paying for a gym membership you have no intention of using, cancel it and put the money toward retirement. Next, focus on the expenses that are not necessary but that you don't want to eliminate completely. For instance, if you spend $100 per month on dining out, maybe try to cut that back to $50 per month. Or if you normally take two or three vacations each year with the family, you might try traveling in the off season to save money or planning some fun activities closer to home that aren't quite so expensive.

Finally, try to find ways to reduce the necessary expenses in your budget. If you're spending a lot of money on gas during your daily commute, for example, you may be able to save some cash by starting a carpool with some of your nearby coworkers. Or you might save on groceries by using coupons and searching for deals. Each of these changes might not save much on its own, but when you save a little bit in each category of your budget, it can add up to hundreds of dollars per month -- which could be all you need to get your retirement plan back on track.

Saving for retirement is tough, but it's even tougher when you don't know whether you're on the right path. Once you know how much you already have stashed away, it's easier to adjust your retirement plan and reach your goals.