Retirement planning is full of rules of thumb. The 4 percent rule can help you to decide how much to withdraw from your retirement savings each year, and aiming to replace a certain percentage of your pre-retirement income can give you a rough idea of how much to save. However, this well-intentioned advice sometimes gets slowly twisted into something else that does more harm than good. Here are some ways following expert advice can actually harm your financial future.

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You are unlikely to implement the 4 percent rule. The 4 percent rule is based on withdrawing 4 percent of your assets annually and adjusting the amount based on inflation every year. So even if the market does really well or drops precipitously, you stick with a 4 percent withdrawal based on the original nest egg and ride out the bumps. But can you imagine anyone actually doing this throughout retirement? Say you are 20 years into retirement. By then, even the most stubborn and disciplined person has probably come up with a new percentage to draw based on market performance and personal circumstances. In reality, people end up twisting the 4 percent rule, perhaps to withdraw more money when they incur an unexpected expense or skip a withdrawal while the market is down. This may or may not work for them, but it's not the 4 percent rule.

Everyone doesn't need the same percentage of pre-retirement income. Some studies have calculated that most people will need a specific percentage of their pre-retirement income to live comfortably in retirement, such as 75 or 80 percent of working income. This is another rule that could help you get a sense of how much is needed for your retirement years, but it may not work in practice. There are just too many expense variables to say that everyone will be able to get by on a given percentage of their pre-retirement income. For example, many people have a mortgage payment that consumes around 25 percent of their income. Obviously, people who pay off their house before they retire will have a vastly different expense situation than those who are still making payments. Therefore, the only way to come up with any realistic retirement budget is to know your own situation and track your expenses. There's no other way to determine how much you need to save for retirement.

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There's inflation between now and retirement too. While most people consider how inflation will impact their nest egg during their retirement years, not enough people account for inflation eroding their purchasing power from now until the day they decide to start their retirement. Of course, this problem is worst for younger folks who have decades until they retire. But workers nearing retirement should acknowledge that they will probably need a bigger nest egg to account for inflation. Once you figure out your expenses, you need to remember to add inflation into the calculation too. For example, if your expenses are currently $40,000 a year, the same level of consumption could cost as much as $54,000 in 10 years.

Social Security is a big help. It's true that the Social Security system has a long-term deficit. But there is almost no chance that the program will be eliminated in its entirety. This means that, for the vast majority of Americans, there will be some sort of check coming to you on a monthly basis for the rest of your life, and it will be adjusted each year to keep up with inflation. The program won't replace all your working income, but the monthly payments will give your retirement standard of living a significant boost.

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Instead of writing the whole scheme off completely, you should make sure that you are doing what you can to increase your retirement benefit. This means at least 35 years of paying into the system, and taking some time to figure out the pros and cons of claiming your benefits at various ages. Married individuals should explore ways to maximize their lifetime benefit as a couple.

David Ning runs MoneyNing, a personal finance site aimed at helping others change their habits for a better financial future. He suggests that everyone to sign up for an online savings account to get more out of our hard earned money.

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