It's common for retirees to spend less than their working counterparts. After all, many seniors enter retirement mortgage-free, and they don't have to contend with some of the expenses workers face, like commuting costs. But in many cases, spending less in retirement isn't an active choice so much as a necessity resulting from not having enough income. And not having enough income in retirement often stems from not having planned appropriately for it -- something 55% of seniors are bemoaning at present.

Where did today's retirees go wrong? According to a survey by Global Atlantic Financial Group, here are Americans' top three retirement-planning regrets.

1. Not saving enough

An estimated 36% of retirees believe they didn't save adequately for their golden years. A report by the Economic Policy Institute released a few years back found that the average baby boomer was entering retirement with a mere $163,577 socked away. At a 4% annual withdrawal rate, which financial experts have long recommended, that translates into just $6,543 of yearly income. Of course, many seniors have income outside of an IRA or 401(k), such as Social Security benefits, other investments, and even their homes (for those who can rent them out or use them to secure a reverse mortgage). Still, it certainly makes the case to enter retirement with far more than $163,000 and change.

Older man with sad expression

Image source: Getty Images.

The good news, however, is that annual IRA and 401(k) contribution limits are pretty generous these days, so if you're willing to cut expenses in your budget to free up more cash to sock away, you can boost your savings tremendously. Beginning in 2019, workers under 50 can save up to $6,000 a year in an IRA and $19,000 a year in a 401(k). Those 50 and over, meanwhile, get a catch-up provision that increases these limits to $7,000 and $25,000, respectively.

Let's say you're 55 with just $50,000 saved in a 401(k), and your goal is to retire at 67. If you were to max out your 401(k) for the next 12 years at an average annual 7% return (doable if you invest heavily in stocks), you'd bring your total savings balance up to about $560,000. When we apply a 4% annual withdrawal rate to that sum, we get $22,400 in yearly retirement income. And that paints a much nicer picture.

2. Relying too heavily on Social Security

Though Social Security is a crucial income source for millions of Americans, it was never designed to pay for retirement by itself. Yet 20% of those surveyed admit to having relied too heavily on Social Security.

If you're still working, know this: Social Security will replace only about 40% of your pre-retirement income as an average earner (if you're a higher earner, it will replace even less). Most seniors, however, need about double that amount to live comfortably, which means that you must save to make up that difference.

In our previous example, we ran through a catch-up scenario that required our hypothetical saver to max out a 401(k) for 12 years to retire with a decent-sized nest egg. If you're already on the older side, you might need to do the same. If you're younger, however, you can amass a nice amount of wealth through a steady stream of smaller contributions over time, as the following table shows:

Age When You Start Saving $400 per Month

Total Retirement Savings at Age 67 (Assumes a 7% Average Annual Return)

22

$1.37 million

27

$958,000

32

$663,000

37

$453,000

As you can see, saving just $400 a month, or $4,800 a year, will go a long way over time. Wait too long, and you'll need to play catch-up, since Social Security alone won't cut it.

3. Not paying down debt before retirement

Unless you're planning to work during your golden years, being retired means living on a fixed income. And the more debt payments you have to monopolize your limited funds, the more financial stress you're apt to experience. It's not surprising, then, that 12% of retirees wish they had knocked out their debt before leaving the workforce.

If you're looking at retiring soon and are in debt, it pays to cut back on spending in the coming years and use your savings to chip away at your various balances. But be sure to start with your credit cards. Tempting as it may be to enter retirement mortgage-free, chances are you're paying a lot higher interest on your credit card balances than you are on your home loan. Furthermore, while mortgage debt is considered the good kind that can help your credit (provided you're on time with your payments), credit card debt can hurt your credit -- which could be problematic should the need to borrow in retirement arise.

The last thing you want to do as a senior is look back on your working years with regret. Don't let that happen. Save consistently, understand Social Security's limitations, and get out of debt. Doing so could be the key to enjoying retirement to the fullest.