Many seniors enter retirement and wind up miserable early on. The reason? Money worries.

Adjusting to a fixed income is no easy feat, and a lot of older Americans wind up struggling financially when they realize just how expensive retirement is. If you'd rather avoid that fate and instead coast through your senior years, here are three important moves to make.

Smiling older man holding mug outdoors.

Image source: Getty Images.

1. Research your costs

It's easy to assume that your living expenses will largely stay the same once you leave the workforce, especially if you plan to maintain a similar lifestyle to the one you're used to. But you may be forgetting one key expense: healthcare. It's the one thing that's likely to cost much more as you age, and knowing what to expect can help you avoid unpleasant financial surprises.

HealthView Services, a provider of cost-projection software, estimates that the average healthy 65-year-old couple retiring in 2021 will spend a total of $662,156 on medical care during retirement. Separate data from the Senior Citizens League tells us that 66% of today's seniors are spending more than $375 a month on healthcare.

Plan for that expense so it doesn't wreck your retirement budget. A good bet is to fund a health savings account during your working years if you're eligible. Enrollment hinges on having a high-deductible health insurance plan that meets other requirements.

2. Save from an early age

Entering retirement with a robust nest egg is a good way to keep your financial concerns to a minimum. And saving from a young age could be your ticket to a hefty pile of cash.

In fact, you can amass a large sum of wealth even if you're an average earner. If you sock away $500 a month in a retirement plan for 45 years, and your investments generate an average annual 7% return (more on that in a bit), you'll wind up with over $1.7 million. Start saving 10 years later, and you'll be looking at about $830,000, all other things being equal.

3. Invest aggressively while you can

Taking on some risk in your IRA or 401(k) could lead to big rewards, so it pays to go heavy on stocks throughout your career. As retirement nears, you'll definitely want to look at shifting to safer investments, like bonds, but for the bulk of your savings window, stocks are really the way to go.

In the example above, we saw that a 7% average annual return helped 45 years of $500 monthly contributions grow to $1.7 million. That 7% is a bit below the stock market's average.

Now, watch what happens when we apply a 5% return, which is far more conservative. Suddenly, that $1.7 million balance drops to $958,000. That's still a nice chunk of cash, but it won't buy you the same financial security as $1.7 million.

Don't let money woes wreck your retirement

If you want to spend your senior years enjoying the freedom of not having a boss to report to, you'll need to set yourself up for that during your time in the workforce. That means getting educated on how much income you'll need in retirement, saving from a young age, and investing your money wisely.

Do those things, and chances are you won't relate at all when your fellow retirees start moaning about the ever-climbing cost of milk.