Social Security benefits are a lifeline for millions of retirees, but they're not guaranteed. Not everyone is eligible to collect Social Security, and if you don't qualify, you may need to save more than you think to make ends meet in retirement.

If you expect to rely on your benefits in retirement, it's best to double-check that you're entitled to receive them. If you fall into any of these three groups, you may not qualify for Social Security benefits at all.

Social Security card with assorted bills and coins.

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1. You haven't worked long enough

In order to qualify for retirement benefits, you have to have worked and paid Social Security taxes long enough to earn 40 credits. You can earn up to four credits per year, so most workers are eligible for benefits after working for 10 full years.

If you haven't worked and paid Social Security taxes for at least 10 years, you don't qualify for benefits based on your own work record.

2. You owe too much money

Certain types of debt can potentially reduce your benefits, and if you owe a lot of money, you may receive little to nothing from Social Security.

If you've defaulted on federal student loans, for instance, the government can garnish a portion of your Social Security benefits to repay your debt. The federal government can also garnish up to 15% of your benefits if you owe back taxes.

In addition, your retirement benefits could be garnished if you owe alimony or child support payments. If you owe a lot of money in unpaid loans, taxes, alimony, or child support, you could have the majority of your benefits withheld to cover these debts.

3. You move to a country where you're not eligible to receive benefits

If you're entitled to Social Security benefits but move outside of the United States, you're generally still able to collect your checks in your new country of residence. However, there are certain countries where the Social Security Administration is unable to send benefits.

For example, the Treasury Department prohibits sending Social Security payments to U.S. citizens living in Cuba or North Korea. There are several other countries with restrictions on receiving Social Security benefits -- such as Moldova, Belarus, and Kazakhstan -- although some beneficiaries can qualify for exemptions.

If you live in any of these restricted countries and don't qualify for an exemption, you won't receive Social Security benefits until you move to a different country that allows payments.

Making the most of your benefits

Before you retire, it's wise to make sure you're entitled to Social Security benefits. Double-check that you've worked long enough to qualify, and determine whether any unpaid debts could affect your benefits. Finally, if you're planning on moving to a new country in retirement, make sure you're still able to collect Social Security in your new residence.

By doing your research now, you can avoid any Social Security surprises in retirement and enjoy your senior years as comfortably as possible.