4 Common Personal Finance Tips That Will Actually Fail You

When it comes to money, there's a lot of advice out there that's repeated over and over. While some of this advice is great, there are also situations where the conventional wisdom is wrong. Unfortunately, if you rely on myths to make important choices about your money, you could end up in a very bad situation.

It's important to research financial decisions carefully and to question the status quo to make sure you do what's best for you. In particular, there are four pieces of common financial advice you likely don't want to rely on because they're probably wrong.

Broken piggy bank with coins spilled out.
Broken piggy bank with coins spilled out.

Image source: Getty Images.

1. Save 10% of your income for retirement

You've probably heard many times that you should save 10% of your income for retirement. Sadly, when you actually do the math, you'll discover this is likely to leave you with far too little income to sustain your lifestyle after leaving work.

Saving 10% of income simply isn't enough to provide the funds you need as a senior. Say, for example, you start saving at the age of 30 when you're earning $35,000. If you get 2% annual raises, invest 10% of income, and earn a 7% return on investments as a pre-retiree and a 4% return on investments during retirement, you'd end up with $440,827 saved by age 62. If you needed to replace 90% of pre-retirement income and receive an estimated $21,883 in Social Security benefits, you'd run out of money by age 75, assuming a 2.9% inflation rate.

Having a higher income won't help. Assuming all the same parameters, having an income of $60,000 at age 30 and a Social Security benefit of $30,848 at 62 would leave you running out of money by 73. You'd run out of money sooner because you'd have a higher income to maintain post-retirement and, as your salary increases, Social Security replaces less of your pre-retirement income.

To make sure you've got sufficient savings, it's best to aim to save at least 15% of income for retirement, but more is always better.

2. The 4% rule means you won't run out of money

Conventional wisdom also says you're safe to withdraw 4% of your income from retirement savings during your first year and then increase withdrawals based on inflation each year.

But research from Morningstar Investment Management conducted in 2013 found that with bond yields below historical averages, the 4% rule only provides a 50% probability of success. In other words, it's 50-50 whether you'll run out of cash if you follow it. To have a 90% chance of not running out of money, you'd need to follow a 2.8% rule instead.