Seniors who are eligible for Social Security get a range of choices when it comes to filing for benefits. In fact, once you turn 62, you can claim benefits at any time. There's technically no "final age" to sign up for Social Security, though there's no financial benefit to delaying a filing beyond the age of 70.

You may, however, be inclined to sign up for Social Security at age 65 since that's when Medicare eligibility first begins. To be clear, you don't necessarily have to enroll in Medicare at age 65. In some cases, waiting to enroll could make sense (though in some cases, waiting too long could also mean facing lifelong surcharges on Medicare premiums). Generally speaking, though, age 65 is a popular one at which to sign up for Medicare, so at that point, you may be eager to file for Social Security as well.

A person at a desk.

Image source: Getty Images.

But while claiming Social Security at age 65 might seem like a move that makes sense, it could end up backfiring on you big time for one big reason.

When you end up slashing your benefits for life

Although you're allowed to file for Social Security beginning at age 62, you're not entitled to your full monthly benefit based on your personal income history until you reach full retirement age, or FRA. FRA is 67 if you were born in 1960 or later.

If you claim Social Security at age 65 -- whether in conjunction with signing up for Medicare or not -- you'll slash your benefits by about 13.34% if your FRA is 67. This means that if you'd normally be eligible for a $2,000 benefit at age 67, a filing at 65 would leave you with $1,733 a month instead -- forever. That could result in a lot of lost income in the course of your retirement.

It's one thing if you've been forced out of your job at age 65 and need money from Social Security to stay afloat. In that case, filing for benefits early is a better bet than racking up costly credit card debt just to pay the bills.

But you shouldn't rush to claim Social Security at age 65 simply because you're ready to sign up for Medicare. You can absolutely become a Medicare enrollee without beginning your Social Security benefits.

Seniors who are signed up for Medicare and Social Security at the same time have their Medicare premiums for Part B, which covers outpatient services, deducted from their monthly benefits automatically. But if you're not on Social Security at the time you enroll in Medicare, it's not a problem. You can just pay your Part B premiums directly in that case and sit tight on Social Security until you're eligible for your monthly benefit in full.

A mistake you might regret

You may end up relying on Social Security for the rest of your life once your benefits start coming in. So slashing those benefits with an early claim is a move that might hurt you tremendously.

Signing up for Medicare and Social Security simultaneously might seem like a nice, convenient route to take. But it's a decision that could end up hurting you for the rest of your retirement.