For 51 million retired Americans, Social Security provides a crucial safety net, distributing $1.5 trillion in benefits. They are a vital source of income for many, with 1 in 7 retirees relying on them for nearly all of their income. Let's take a closer look at some things you should know.

A lot goes into determining how much you see in your check each month

Your primary insurance amount (PIA) is based on the average of your 35 highest-earning years of work. If you worked fewer than 35 years, each year without work counts as zero, which lowers your average and subsequently your benefits.

When you choose to retire is a critical choice as it can greatly impact your benefits. You receive your full PIA only if you retire at your full retirement age (FRA). The FRA is 65 for those born before 1937; it's 66 for those born between 1943 and 1954; and it's 67 for those born after 1960. If you were born between 1954 and 1960, it is somewhere between 66 and 67. You can see a full chart here.

If you choose to claim benefits early, at age 62, your benefits will be reduced by as much as 30%. However, if you delay claiming benefits until age 70, you can receive up to 124% of your normal PIA. So those who can afford to hold off until that point will benefit from doing so.

Here's the average

On average, retirees at age 75 receive a monthly benefit of $2,012.14. However, this amount can vary significantly based on your earnings history and the age at which you begin to claim benefits. For most retirees -- and those preparing for that day -- it's important to build up additional sources of retirement income, such as a 401(k) or IRA.