According to a Gallup poll, less than a third of Americans have long-term financial plans, which is concerning. Failing to consider critical factors could lead to not saving enough money and watching the well run dry during your golden years.

Man sitting at table with dollar bills and coins in front of him

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There are plenty of big questions to ask yourself when planning for retirement, such as what age you plan to retire at and how much you'll be earning in Social Security benefits. But there are also less obvious factors to consider as well, and making these mistakes can have a serious impact on your retirement.

1. Forgetting about inflation

It's hard enough to create a budget for the next 30 days, so of course figuring out how much you'll need during retirement 30 years in advance may seem like an impossible task. It doesn't stop there, though -- inflation can further complicate things.

The U.S. inflation rate typically hovers around 2% to 3% per year, That may not seem like much, but when you consider how many years you have until retirement and how many years you'll spend in retirement, it adds up. For example, say you're 40 years old and have $50,000 saved for retirement. By the time you turn 65, assuming an inflation rate of 2% per year, that $50,000 will only be worth around $30,476. Once you turn 80, that $50,000 will be worth approximately $22,644.

In other words, while you may think you're saving a ton of money, that's in today's dollars; in a few decades, that money won't go nearly as far as you may think.

What does that mean for your retirement roadmap? Basically, you'll need to save a lot more than you may have initially thought. While that news probably doesn't have you jumping for joy, if you catch this mistake early and start accounting for inflation in your savings plan, you will be a much happier retiree.

The best way to plan for inflation is to begin with a retirement budget. Look at the last few months of bank and credit card statements to get an idea of how much you spend now, then use that as a basis for how much you'll be spending during retirement. Once you have that number, you can add in inflation costs. So, for instance, if you calculate that you'll be spending $3,000 per month during retirement, assuming a 2% inflation rate, in 20 years your cost of living will increase to around $4,458 per month.

It's also a good idea to experiment with different inflation rates, because even small differences in inflation can affect your long-term savings. For instance, if you expect to spend $3,000 per month when you retire, if the inflation rate is closer to 4% your cost of living will jump to $6,573 per month after 20 years.

2. Not accounting for long-term care costs

Around 70% of Americans turning 65 in the near future will require long-term care at some point according to the U.S. Department of Health and Human Services. Furthermore, those who require long-term care will each pay an average of $138,000 to cover those costs.

You may only need long-term care for a year or two toward the end of your life, but those costs are significant. And if you don't budget them into your savings, your savings may run dry too early.

While there's no way to predict exactly how much you'll need to pay in long-term care costs (or whether you'll need long-term care at all), it's best to assume the worst and prepare accordingly.

The good news is that if you plan early, it's won't take as much effort to save more to cover these costs. For example, say you're 35 years old and plan on retiring at 65. If you currently have $40,000 saved and are contributing $150 per month earning a 7% annual rate of return on your investments, you'll have around $480,900 by the time you retire. But if you were to contribute an extra $50 per month, you'd end up with about $539,703 after 30 years -- a difference of nearly $60,000, which can go a long way toward covering long-term care costs.

Long-term care insurance is another option, though it can be pricey. If you anticipate needing long-term care in the future, though, it may be a good choice. While long-term care insurance rates vary widely, typically the earlier you sign up, the lower your rates will be. For example, the average 55-year-old couple pays around $2,500 per year combined, while a 60-year-old couple will pay on average $3,400 per year, according to the American Association for Long-Term Care Insurance.

3. Underestimating how long retirement will last

Though it may feel as if you spend far more time in the workforce than in retirement, for some people that may not be the case.

The average worker leaves the workforce at 63 years old, according to Aperion Care, and the average life expectancies for men and women turning 65 today are 84 and 86, respectively. That means the typical retiree spends around 20 years in retirement.

However, a quarter of today's 65-year-olds are expected to live past age 90, according to the Social Security Administration, and one in 10 will make it past 95. While that's great news, it can be detrimental to your retirement fund if you don't plan ahead. If you plan for a 20-year retirement that ends up lasting more than 30 years, those last few years won't be as enjoyable as you'd hoped.

While you'll likely have Social Security benefits to help cover costs, the average beneficiary receives around $1,400 per month -- which may not be enough to cover everything. Especially considering the fact that you'll likely develop more (expensive) health issues as you age.

The safest bet is to plan ahead for a long retirement. If you assume you'll spend, say, 30 years in retirement and only end up living 25 years, you'll just end up with some extra cash -- which is far better than the alternative of outliving your money.

Once you do retire, it's also important to do a yearly checkup on your budget and retirement fund. Are you spending about as much as you had planned? Maybe you find that your monthly expenses are higher than you had anticipated, in which case your retirement savings may not last as long as you had hoped.

If you notice these discrepancies early, you can do something about them before it's too late. Perhaps pick up a part-time job to boost your savings, or downsize to a smaller home to cut costs. The worst case scenario is to have no idea how long your savings will last until you run out of money -- when it's too late to go back to work or save more.

Saving for retirement is a science, and it's not easy. There are a multitude of factors to consider, and even small mistakes can compound over time. But the more prepared you are before retirement, the more enjoyable your golden years will be.