Taylor Hill/Getty Images Moneywise and Yahoo Finance LLC may earn commission or revenue through links in the content below. How much money do you really need to retire without losing sleep at night? If you think your 401(k) alone will cut it, think again — one wrong market move could put your retirement plan to sleep. But figuring out how much you’ll need to enjoy your retirement isn’t straightforward. The costs can add up fast between health care, housing, groceries and maybe even a vacation or two. M ...