After a friend recently mentioned his path to a $2 million net worth, it raised two key questions: How much do you really have to save to become a multimillionaire? And is it really achievable within a working lifetime?

The amount you need to save each month to reach that milestone depends on two key factors. The first is how much time you have between now and when you're no longer able to sock away money. The second is what rate of return you'll earn on your investments. Still, that $2 million net worth is within the reach of most people if they start early enough and invest consistently enough throughout their careers.

Well-dressed couple with champagne in front of a helicopter.

Image source: Getty Images

How much is enough?

The table below shows how much you'll have to invest each month to reach that $2 million milestone, depending on what rate of return you earn along the way:

Years to Go

9.6% Annual Returns

8% Annual Returns

6% Annual Returns

4% Annual Returns

45

$218

$377

$722

$1,321

40

$354

$569

$999

$1,686

35

$579

$866

$1,397

$2,182

30

$956

$1,333

$1,981

$2,872

25

$1,600

$2,089

$2,872

$3,877

20

$2,751

$3,373

$4,307

$5,435

15

$4,966

$5,741

$6,843

$8,100

10

$9,910

$10,860

$12,143

$13,537

Table by Author.

Over the long run, the stock market has delivered returns around that 9.6% annualized pace. That indicates that the friend who reached that $2 million milestone by investing heavily in stocks and stock funds likely did so by investing around $2,751 each month –- an impressive but not impossible level.

If your timeline is longer, you can get away with saving less -- much less, in fact -- and still wind up a multimillionaire. But if you have less time remaining in your working career, the challenge gets substantially tougher -- to the point where even very high earners would find it an uphill battle.

How can you save that much?

While the numbers farther down the list may seem daunting, your boss and Uncle Sam may be working together to help you come up with that kind of cash. Between your 401(k) and your IRA -- and your spouse's, too, if you're married and your spouse works -- it's possible to save thousands each month in a tax-advantaged way. If your boss also kicks in with a match to your 401(k) contribution, it's also counted toward that total, reducing your own out-of-pocket costs of getting there.

In an IRA, typical workers can contribute $5,500 per year as of 2018 if they're under age 50, or $6,500 per year if they've reached age 50 or higher. That's $458 and $541 per month, respectively. You do need a salary or other form of earned income to contribute to an IRA, but if you're married and only one spouse works, you can likely contribute to a spousal IRA for the benefit of the nonworking spouse.

Inside of a 401(k), the contribution limit as of 2018 for workers under age 50 is $18,500 per year, and for workers age 50 or older, it's $24,500 per year. The numbers are potentially reduced if you're considered a highly compensated employee. For most of us, though, that works out to $1,541 and $2,041 per month, respectively, before factoring in any match the company may provide.

A single person under age 50 can save around $2,000 per month in tax-advantaged accounts, and at 50 or older, that increases to $2,580 per month. If you're married with both spouses working, those numbers double to $4,000 for those under age 50 and over $5,160 for those who've reached that milestone age. That puts reaching multimillionaire status within potential reach using retirement accounts alone for a 50-ish-year-old duel-career couple with 15 working years left, if they're able to save aggressively.

How important is it to you?

Reaching a $2 million net worth is a challenging goal. Nevertheless, it is likely achievable if you start early or commit a significant amount of money to it over a time frame that can be measured in decades. If you want to stretch for that milestone, one thing is certain: The sooner you start, the less money you'll likely have to sock away each month and in total to reach that goal.

And if you choose to pursue or wind up at a lower target, fear not: You probably don't need nearly that much to retire to a reasonable lifestyle. Combine Social Security, Medicare, a paid-off house, and independent grown children, and you'll likely find that a smaller nest egg will get you what you truly need in your golden years.

Still, it's good to know how much you have to save to become a multimillionaire. If you want to work toward that target, it helps to know what sort of choices you'll have to make along the way.

The Motley Fool has a disclosure policy.