In the course of planning for your senior years, you'll surely know to account for certain unavoidable expenses -- housing, transportation, meals, and the like. While some of your retirement expenses may be fairly predictable, here are a few that could end up being much costlier than expected. Consider yourself warned.

1. Taxes

Your tax rate as a senior will depend on your total income. If you have a healthy amount of it between your Social Security benefits, retirement plan withdrawals, and other sources, your tax bill may be a lot higher than expected.

Read up on the various types of retirement income that get taxed so you're not caught off guard. For example, Roth IRA and 401(k) withdrawals are yours to enjoy tax-free, whereas traditional retirement plan distributions are taxable. Furthermore, if Social Security isn't your sole or primary source of income, there's a good chance you'll pay taxes on those benefits as well.

To avoid having taxes constitute a major burden, plan wisely. Save in a Roth retirement plan and look at moving to a state with no or low income taxes. Similarly, you may want to avoid states that tax Social Security benefits.

Older couple looking at laptop with concerned expressions.

Image source: Getty Images.

2. Healthcare

Medicare Part A, which covers hospital care, is free for most enrollees. However, Part B, which covers outpatient services, charges a monthly premium, as does Part D, which covers prescriptions. And that's just the tip of the iceberg.

You'll also be on the hook for deductibles under both Parts A and B, coinsurance, and other costs, so don't expect medical care to be cheaper during retirement than it is during your working years. In fact, the average healthy 65-year-old couple leaving the workforce this year can expect to spend $662,156 on medical bills in the course of retirement. Ouch.

To avoid a cash crunch, set funds aside in a health savings account (HSA) if you're eligible for one (you can participate if you're enrolled in a high deductible health insurance plan). If you can't fund an HSA, aim to max out your IRA -- or, better yet, your 401(k) plan, which has higher contribution limits -- so you have extra money to cover healthcare costs down the line.

3. Long-term care

The average 65-year-old today has close to a 70% chance of needing long-term care at some point during retirement. While the cost of that care can vary tremendously based on specific needs, duration, and location, the average senior spends $172,000 to cover it.

To steer clear of financial problems later in life, apply for long-term care insurance during your 50s. While you will shell out some money for a policy, having one in place will protect you if you wind up needing extended care in a costly facility. Of course, it never hurts to pad your IRA or 401(k) so you have more money to cover whatever care you wind up needing later in life.

You can plan for retirement all you want, but if you fail to accurately account for your costs, you're apt to wind up financially stressed. Now that these expenses are on your radar, be sure to read up on what they might amount to so you can go into your senior years prepared.