The median amount baby boomers have saved for retirement is just $152,000, according to a report from the Transamerica Center for Retirement Studies. That may sound like a healthy chunk of change, but depending on how much you spend each year in retirement, that nest egg may only last a few years.

There's also a chance, however, that your retirement investments are worth less than you think. And by ignoring this one subtle factor, you could have less disposable income than you expect in retirement.

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The sneaky detail that can dramatically limit your retirement income

As you're preparing for retirement, it's easy to fall into the habit of looking at your savings in terms of today's dollars. However, if you're not accounting for inflation in your retirement plan, your money may not go as far as you think.

The U.S. inflation rate typically hovers around 2% to 3% per year. That may not sound like much, but even slight spikes in inflation can cause your money to lose value over time. For example, $50,000 in today's dollars would be worth around $82,000 in 25 years, assuming a 2% inflation rate, according to research from Fidelity Investments. But with a 4% annual inflation rate, something that costs $50,000 today would cost more than $133,000 in 25 years.

Inflation can make it more challenging to prepare for retirement for a couple of reasons. For one, it can make your savings look stronger than they actually are. If you have hundreds of thousands of dollars saved for retirement, you may be tempted to sit back and relax, thinking that's plenty to last the rest of your life. In reality, though, a few decades down the road after inflation has taken its toll on your savings, that money won't be worth nearly as much as it is now.

In addition, it can be tough to predict how much you'll need to save when you're still decades from retirement. If you're in your 30s now, for instance, it's challenging enough to figure out how inflation will affect your savings by the time you're ready to retire. It's next to impossible to predict exactly how much your money will be worth 50 or 60 years down the road during your final years of retirement. However, that doesn't mean that you shouldn't try your best to account for inflation as you're preparing for retirement.

How inflation factors into your retirement plan

Although you may not be able to predict exactly how inflation will impact your savings, you can prepare for it as much as possible. To do this, use a retirement calculator to estimate how much you should aim to save by the time you retire. 

Most calculators allow you to adjust the future inflation rate, which will affect how much you should save. To err on the side of caution, input a higher-than-average inflation rate (or a rate higher than 3%). This will mean you'll need to save more for retirement, but it also means your savings are more protected against inflation. If you input an average or lower-than-average inflation rate, you won't need to save as much now. However, if inflation spikes between now and the end of your life, you also risk running out of savings too soon if your money loses a significant amount of value.

Inflation is a sneaky cost that can be difficult to prepare for, but the last thing you want to do is not account for it at all in your retirement plan. By using a retirement calculator to estimate how inflation will impact your savings, you can go into retirement as prepared as possible.