Retirement is a big decision. You don't want to rush into leaving work, only to find yourself broke and struggling to get back into the job market.

To make sure that doesn't happen, you'll need to think about all of the costs you must pay as a retiree. Unfortunately, many people overlook three potentially substantial expenses they should plan for.

Here's what they are.

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1. Taxes

While you won't be getting a paycheck anymore, your obligations to the IRS don't disappear when you're retired. Unfortunately, many people forget that the federal government (and sometimes their state government) still wants its cut.

You must know exactly what sources of income will be taxable, and how much you'll be able to bring home from your investment accounts and Social Security after accounting for taxes. For example, depending on your income, up to 85% of Social Security benefits could be subject to federal income tax -- and a minority of states also tax Social Security too.

Distributions from a traditional 401(k) and IRA are also treated as taxable income, although distributions from Roth accounts are not. You can research your tax rate and how the income you'll be relying on is taxed to estimate your future IRS bill. If you don't have enough money coming from Social Security and your retirement plans after paying the tax, then you aren't ready to retire.

2. Medical care

Medical care is another big expense you can't afford to overlook.

While Medicare provides coverage starting at 65, you still have Medicare premiums to pay -- not to mention potentially substantial out-of-pocket expenses for things that Medicare doesn't cover. That includes things like long-term care and even more basic healthcare needs, like dental care and hearing aids.

Fidelity estimates that the costs of medical care will average $172,500 for a 65-year-old retiring in 2025. And that's just for things like Medicare premiums, coinsurance costs, and services that are not covered. Long-term care could be hundreds of thousands of dollars more.

3. Inflation

Finally, you need to consider the indirect costs of inflation. Inflation ends up raising the prices of everything that you buy. If your investments, savings, and Social Security benefits don't increase each year enough to keep pace with inflation, you lose buying power.

Your investment portfolio ideally will earn generous enough returns that you don't lose ground, but your money in savings and bank accounts probably won't. And sadly, despite Social Security cost-of-living adjustments, Social Security benefits aren't really keeping pace with inflation either.

The Senior Citizens League estimates that benefits have lost around 20% of buying power from 2010 to 2024 because the benefits formula used to calculate COLAs is imperfect. It's based on the spending habits of urban wage earners and clerical workers who spend differently from seniors. Since benefits are losing ground, you'll need a large enough nest egg to make up for the shortfall.

Consider whether you have enough money in your retirement plans to deal with these expenses before you retire. Otherwise, you could spend your senior years struggling.