If you claim Social Security benefits after you reach full retirement age, you’ll be offered an up-front payout equal to as much as six months of your benefits. That’s $15,000 if your monthly benefit is $2,500, for example.

But beware: Taking the lump-sum payout will reduce your monthly Social Security payments for the rest of your life. If you accept it, it will be as if you claimed your Social Security benefits six months earlier than you actually did.

Each month that you wait beyond full retirement age—up to age 70—to begin receiving your benefits increases each future monthly payment by two-thirds of 1%, so accepting six months of retroactive benefits would lower your monthly Social Security payments by 4%. Also: Taking that payment might push you into a higher tax bracket for that year and/or increase the percentage of Social Security income subject to income taxes.

But there are circumstances when taking the lump sum might make sense…

You have received terrible medical news. The lump sum can be a way to quickly obtain as much money as possible from the Social Security system.

You waited past age 70 to claim benefits. Taking the lump sum offers a way to recapture up to six months of benefits that otherwise would be lost.

You face debts that you cannot pay. Paying down debts could make more sense than paying high-rate credit card debt, for example.

Important: The lump-sum option is not available to anyone who claims his/her benefits before or precisely at full retirement age. And if you are less than six months past full retirement age when you claim your benefits, the lump sum available will be smaller than the six-months-of-benefits payout described here—retroactive benefits are not available for months prior to the month in which full retirement age is reached. Full retirement age is 66 for people born between 1943 and 1955. For people born in 1956, it is 66 years and four months…for those born in 1957, it is 66 years and six months…and so on until birth year 1960 (and later). For anyone born in or past that year, the retirement age is 67.