While lots of Americans just can’t stretch the budget far enough to put away money for retirement, there is a group among the general population that’s managing not just to save, but to save way more than the average person who does stash funds for the future.

A CNBC report says that “super savers” are not shelling out for a lot of things in a tradeoff that lets them save more money for retirement. It defines super savers as “Americans who are putting aside at least 90 percent of the annual $18,000 employee contribution limit to their 401(k) plan.”

Related: Quick guide to 5 types of financial wellness programs

The report cites a Principal Financial survey that provides some insights into how they managed to put away so much money. Respondents were surveyed in late 2016; all were retirement plan participants, ranging in age from 23–51, had hit super saver status in 2015, and were on track to do it again in 2016.

According to a Vanguard report, only 10 percent of employees actually manage to hit the maximum contribution limit in 2016; that’s fallen from the 13 percent who hit the mark in 2015.

Related: Quiz: Do you know these retirement facts?

Most tend to be both older and wealthier, but Principal looked at the saving achievements of GenXers and millennials who put away 90 percent or more of the IRS maximum amount in their 401(k) accounts ($16,200–$18,000 per year).

Surprisingly, 91 percent listed saving for retirement as one of their main goals, with more than twice as many millennials saying they’re saving for retirement (90 percent) than those who say they’re raising a family (40 percent).

So how did they do it?

By not splurging on wheels, for one thing—47 percent say they’re driving older cars so they can stash that extra money away.

Houses aren’t on the “new” list, either, with 45 percent saying they live in modest homes and 18 percent of millennials renting instead of buying.

They’re not going on vacations, either; 42 percent say they’re traveling less than they’d like to, and they’re stowing the money away in their retirement funds instead.

But you know what they say about all work and no play; 40 percent of super savers say they’re putting up with work-related stress, and more than a quarter (27 percent) also put in extra hours instead of spending time with friends and family.

Hopefully after devoting all this extra effort to saving for retirement, they’ll live long enough to enjoy it and not succumb to stress along the way.