When you make a plan for the income you'll need in retirement, it's important to take all of your essential expenditures into account. Unfortunately, far too many people fail to consider three of the biggest costs they'll likely end up facing in their later years.

To ensure your investment account doesn't fall short of providing the requisite funds, make sure you have a realistic plan for covering these three big expenses.

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1. Healthcare

Retirement savers often assume Medicare will cover healthcare costs for them -- or that they won't need much extra to pay for any expenses Medicare doesn't pay for.

Sadly, this is a huge mistake, as retirees can expect to incur considerable out-of-pocket healthcare expenses in their later years. This is especially true for those who develop health issues at a relatively young age or for anyone who needs a lot of prescription drugs.

When seniors underestimate how much money they need for care, this can have dire consequences. In fact, a recent survey revealed as many as one in seven people on Medicare were forced to go back to work to cover healthcare costs. And this can actually be a best-case scenario, as people often face some of their biggest, most unaffordable medical expenses after they've become too old or sick to work.

Ensuring you have enough money for healthcare allows you to avoid this fate. But that means you must come up with a realistic estimate of the amount of money you'll need for medical expenses -- which could be as high as $300,000 for a senior couple -- and factor this in when setting savings objectives.

2. Taxes

Most people assume their tax rates will fall as they get older, but that's not necessarily true. Tax rates can rise if your retirement income is higher than your income while working. They can also rise if you lose deductions for 401(k) or IRA contributions or for mortgage interest after paying off your home loan. Finally, tax rates are low by historical standards, and the government could decide to raise them.

If your tax rate is higher than you anticipated as a senior, this could come as a huge financial shock that derails your financial security. As if that isn't reason enough to worry, it's also worth keeping in mind that more seniors are subject to taxes on Social Security benefits each year. If you were expecting these benefits to be tax-free and that turns out not to be the case, this could throw off your retirement budget.

Investing in Roth accounts can help you avoid unpleasant surprises related to taxes as a retiree. But if you'll be using a traditional account and your withdrawals and potentially Social Security benefits will be subject to federal and/or state tax, you need to be prepared to cover these costs on top of your other expenses.

3. Long-term care

Finally, many people don't realize there's a high likelihood that they'll need long-term care, or they aren't aware that Medicare won't provide coverage for it.

In fact, around one-third of retirees couldn't pay for even minimal long-term care services. You can't afford to be one of them, since around seven in 10 seniors will eventually need this help.

To be prepared, you'll either need a substantial amount of savings, a plan to get Medicaid coverage while protecting assets, or long-term care insurance.

By making sure you're ready for healthcare, taxes, and long-term care costs, you can avoid derailing your retirement with huge unexpected expenses that drain your accounts dry.

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