The 401(k) is perhaps the most powerful retirement savings tool available to American workers. You can save huge sums of money in it — up to $18,000 per year if you’re under age 50, or $24,000 if you’re 50 or older — and you’ll get some generous tax break for doing so. And assuming you like free money, most employers that offer 401(k)s will also match a portion of their employees contributions.