Nobody wants to reach the end of their life facing regrets. But more than half of older adults (55%) say they have regrets when it comes to retirement planning, according to a survey from Global Atlantic Financial Group.

Although there's no single right way to prepare for retirement, there are plenty of costly mistakes that could endanger your financial future. And these three money moves in particular can lead to "what ifs" when you reach your senior years.

Older couple looking at documents with a calculator

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1. Forgetting about taxes in retirement

If you're saving in a 401(k) or traditional IRA, you'll owe income tax on what you withdraw during retirement. These types of accounts are tax-deferred, meaning you get a tax deduction on your contributions up front but you'll owe tax when you make the withdrawals. By investing in a Roth IRA, on the other hand, you'll pay tax when you make the initial contributions but your withdrawals will be tax-free.

There's also a chance you may owe tax on your Social Security benefits -- at both the state and federal level. Whether or not you do will depend on where you live and how much you're earning in retirement income. The good news is that there are 37 states that don't tax benefits (and West Virginia will join the list by 2022), so there's a good chance you'll be able to avoid the state tax.

But no matter where you live, you may still be subject to federal taxes. To determine whether you'll owe federal taxes, you'll first need to know your combined income -- which is half your annual benefit amount plus all other retirement income (not including Roth IRA withdrawals). If your combined income is higher than $34,000 per year (or $44,000 per year for married couples filing jointly), you may owe tax on up to 85% of your benefits.

2. Not considering healthcare costs

Healthcare can be one of the most significant expenses in retirement. The average retiree pays around $4,300 per year out of pocket, a study from the Center for Retirement Research at Boston College found.

Even if you're covered by Medicare, you'll still face some out-of-pocket costs like premiums, deductibles, co-pays, and co-insurance. Dental, vision, and drug costs also aren't covered under Original Medicare, so unless you want to pay for these yourself, you'll need to spring for additional coverage like Medicare Part D or a Medicare Advantage plan.

Long-term care is another hefty cost many retirees may not be prepared for. Roughly 70% of those 65 and older will need long-term care at some point, according to the U.S. Department of Health and Human Services, and the average semiprivate room in a nursing home costs more than $6,800 per month -- or roughly $82,000 per year. If you're not budgeting for healthcare and long-term care in retirement, you could face a costly surprise later.

3. Not taking full advantage of matching 401(k) contributions

Employer matching 401(k) contributions are essentially free money, so if you're not taking full advantage of them, you could be missing out on thousands of dollars.

Say you're earning $60,000 per year and your employer will match 100% of your 401(k) contributions up to 3% of your salary, or $1,800 per year. If you're only contributing $1,000 per year to your retirement account, your employer will match that amount -- but you're still missing out on an extra $800 per year in free money by not contributing enough to earn the full match.

In addition, it's not only the free money you're missing, but also all the investment gains. For instance, if you're contributing $1,000 per year (plus another $1,000 from your employer), you'd have around $189,000 saved after 30 years, assuming you're earning a 7% annual rate of return. But if you'd saved $1,800 per year to earn the full match, you'd have around $340,000 over that same time period, all other factors remaining the same.

Retirement should be an exciting, joyous time, not one filled with regret. And with a little planning, you can make the best money decisions and live life without asking, "What if?"